**1. Introduction**

In view of the recent growth of the world population and the need for the suitable use and recycling of natural resources, emerging technologies have been continually called upon to present opportunities to address these global challenges. Expanding the benefits and reducing the risks for all, main principle of the planet's sustainability [1].

Metallic nanomaterials have been introduced as emerging technologies to respond to some of the aforementioned challenges. For example, iron and copper nanoparticles (NPs) have been utilized as plant micronutrients. Therefore, due to their success as antifungal and antibacterial, silver NPs have been applied to control phytopathogens and extend the vase life of some flowers [2]. Metallic NPs have also been used as nano-pesticides to increase the dispersion and wettability of agricultural formulations and unwanted pesticide movement [1, 3].

Besides the above mentioned, while some metallic NPs may have positive effects upon plant systems, it is also possible that this class of NPs has negative implications for plant systems. For instance, barriers to growth for plant systems may occur, negative impact soil microbial structure or function, directly or indirectly alter the formation of symbiotic associations with root fungi and bacteria, influencing nutrient availability and uptake, and plant growth [1].

A nanomaterial gaining popularity is zinc oxide (ZnO), the third metal-containing nanomaterial most commonly used [4–6]. The ZnO nanoparticle is considered multifunctional because it has high chemical stability, wide ultraviolet radiation absorption range and high photostability, and antifungal activity. Such properties allow this nanoparticle to be used to manufacture clothes with ultraviolet (UV) filters, sunscreens, baby rash ointments, paints, and even as food preservatives [7].

The ZnO NPs wide spectrum of applications makes it susceptible to entering the environment through various paths, such as effluents, spillage during transport, handling, direct contact through topical and oral consumer products, and incorrect disposal [8]. Such factors lead to contamination of environments and consequently adverse effects for humans and animals, such as excessive induction of reactive species, which can cause oxidative stress and trigger a cascade of damage in macromolecules, genotoxicity, apoptosis, neurotoxicity, and negative implications for embryonic development [9, 10]. We have shown that amorphous zinc oxide nanoparticles have greater genotoxicity than crystalline (nanocrystals - NCs) [11]. Besides, we have demonstrated its biocompatibility through intraosseous implants [12]. However, the search for nanomaterials with hybrid properties has been standing out even more in recent years.

Doping is a technique that makes it possible to incorporate substitutional ions into the crystalline structure of materials, generating exciting properties [13]. The transition metals are elements whose corresponding atoms do not have a more energetic "d" orbital filled or capable of forming cations with an incomplete d orbital. Therefore, the incorporation of these metals in nanocrystals makes it possible to mix properties, such as magneto-optics [refs]. In addition to this property, other properties are observed, some of which we will show in this chapter. In particular, we will show results of pure ZnO nanocrystals and doped with transition metals and that depending on the dopant, specific properties may or not be improved.

Depending on the doping ion, the nanoparticles' toxicity may be reduced [14]. Copper (Cu) is one of the transition metals with the lowest toxicity to humans, which allows its application in medicine when used in intrauterine devices, and its antibacterial activity [14, 15]. Thus, in the present work, the ZnO NCs were doped with the copper transition metal (Cu doped ZnO) and reduction of toxicity due to doping. To evaluate the biocompatibility of this new nanoparticle, we analyzed the development of the fruit fly (*Drosophila melanogaster*) in a medium containing ZnO or Cu doped ZnO.

*Drosophila melanogaster*, known as fruit fly, is a well-established model organism in several areas of science, including nanotoxicology [16]. It offers several mutant lines for a broad range of human diseases, has low cost and easy maintenance in the laboratory, and a short life cycle compared to other model organisms such as mammals and fish. These features make the fruit fly a great model for studies

**85**

found in natural waters.

emerging pollutants.

removal kinetics.

*Transition Metals Doped Nanocrystals: Synthesis, Characterization, and Applications*

that evaluate long-term and developmental effects, which is still poorly studied in nanotoxicology [16]. The fruit fly also has 77% of the conserved genes related to human diseases [17] and considerable similarities with humans in different physiological mechanisms [18]. In addition, the use of *Drosophila melanogaster* as a model organism in nanotoxicology studies respects the Three Rs concept (Replacement, Reduction, and Refinement) as recommended by the European Center for the

In some technological applications, it is essential that the nanocrystals are embedded in resistant and thermally and chemically stable systems, so the glass systems are excellent hosts [20, 21]. These nanocrystals can be doped with transition metals, aiming for several applications, such as the production of light-emitting diodes, photodetectors, spintronic, and others [21–24]. Therefore, this chapter will comment on the group results of nanocrystals doped with transition metals in the host glass matrix and how the dopant concentration modulates these properties. Therefore, this chapter shows how the incorporation of transition metals in nanocrystals can change their physical, chemical, and biological properties. In particular, iron or copper-doped ZnO nanopowders and chromium-doped Bi2S3 nickel-doped ZnTe, and manganese-doped CdTe in the host glass matrices.

**1.1 Iron-doped ZnO nanocrystals: development and applications**

An important application using nanoparticles comes from environmental remediation. The accelerated population growth and the deficiency in basic

Synthetic and natural estrogens, antibiotics, pesticides, among others, are considered emerging pollutants. The degradation of emerging pollutants by conventional processes is hampered due to low concentrations and their molecular complexity. Thus, the study of new treatment proposals becomes very relevant, such as the application of metallic nanoparticles and catalysts for the degradation of

**Figure 1(a)** shows the Illustrative scheme of crystalline structure of ZnO and the substitutional incorporation of iron (Fe) ions in the nanocrystal. **Figure 1(b)** shows the removals of the pollutant as a function of reaction time, and the different domains studied. The ZnO:11Fe material obtained the highest percentage of degradation, around 74.74% removal, followed by the pure ZnO nanoparticle. It is observed that all materials have similar behavior in reducing the pollutant absorbance. In this case, the different proportions of iron-doped ZnO NCs did not produce relevant effects in terms of efficiency, with all nanomaterials studied showing close percentages and

**1.2 Copper-doped ZnO nanocrystals: development and biocompatibility**

it is the most common form of exposure to the ZnO NC in humans [8].

The availability of various nanomaterials is increasing significantly, and contact with them is inevitable. Thus, it is necessary to determine its direct impact on the human body and the environment. The oral administration route chosen for the in vivo bioassay allows the observation of natural responses of the organism, [25], and

sanitation, and the growth of industrial and agricultural activities have produced an increase in the pollution of the environment due to the generation of large residues that, when improperly treated, present high toxicity. In addition to the classic problems associated with contamination by priority pollutants, there is currently a considerable concern involving micropollutants considered emerging due to the inefficiency in their removal in conventional sewage treatment systems, thus often

*DOI: http://dx.doi.org/10.5772/intechopen.97326*

Validation of Alternative Methods (ECVAM) [19].

#### *Transition Metals Doped Nanocrystals: Synthesis, Characterization, and Applications DOI: http://dx.doi.org/10.5772/intechopen.97326*

that evaluate long-term and developmental effects, which is still poorly studied in nanotoxicology [16]. The fruit fly also has 77% of the conserved genes related to human diseases [17] and considerable similarities with humans in different physiological mechanisms [18]. In addition, the use of *Drosophila melanogaster* as a model organism in nanotoxicology studies respects the Three Rs concept (Replacement, Reduction, and Refinement) as recommended by the European Center for the Validation of Alternative Methods (ECVAM) [19].

In some technological applications, it is essential that the nanocrystals are embedded in resistant and thermally and chemically stable systems, so the glass systems are excellent hosts [20, 21]. These nanocrystals can be doped with transition metals, aiming for several applications, such as the production of light-emitting diodes, photodetectors, spintronic, and others [21–24]. Therefore, this chapter will comment on the group results of nanocrystals doped with transition metals in the host glass matrix and how the dopant concentration modulates these properties.

Therefore, this chapter shows how the incorporation of transition metals in nanocrystals can change their physical, chemical, and biological properties. In particular, iron or copper-doped ZnO nanopowders and chromium-doped Bi2S3 nickel-doped ZnTe, and manganese-doped CdTe in the host glass matrices.

#### **1.1 Iron-doped ZnO nanocrystals: development and applications**

An important application using nanoparticles comes from environmental remediation. The accelerated population growth and the deficiency in basic sanitation, and the growth of industrial and agricultural activities have produced an increase in the pollution of the environment due to the generation of large residues that, when improperly treated, present high toxicity. In addition to the classic problems associated with contamination by priority pollutants, there is currently a considerable concern involving micropollutants considered emerging due to the inefficiency in their removal in conventional sewage treatment systems, thus often found in natural waters.

Synthetic and natural estrogens, antibiotics, pesticides, among others, are considered emerging pollutants. The degradation of emerging pollutants by conventional processes is hampered due to low concentrations and their molecular complexity. Thus, the study of new treatment proposals becomes very relevant, such as the application of metallic nanoparticles and catalysts for the degradation of emerging pollutants.

**Figure 1(a)** shows the Illustrative scheme of crystalline structure of ZnO and the substitutional incorporation of iron (Fe) ions in the nanocrystal. **Figure 1(b)** shows the removals of the pollutant as a function of reaction time, and the different domains studied. The ZnO:11Fe material obtained the highest percentage of degradation, around 74.74% removal, followed by the pure ZnO nanoparticle. It is observed that all materials have similar behavior in reducing the pollutant absorbance. In this case, the different proportions of iron-doped ZnO NCs did not produce relevant effects in terms of efficiency, with all nanomaterials studied showing close percentages and removal kinetics.

#### **1.2 Copper-doped ZnO nanocrystals: development and biocompatibility**

The availability of various nanomaterials is increasing significantly, and contact with them is inevitable. Thus, it is necessary to determine its direct impact on the human body and the environment. The oral administration route chosen for the in vivo bioassay allows the observation of natural responses of the organism, [25], and it is the most common form of exposure to the ZnO NC in humans [8].

*Transition Metal Compounds - Synthesis, Properties, and Application*

tural formulations and unwanted pesticide movement [1, 3].

ent availability and uptake, and plant growth [1].

ing out even more in recent years.

Metallic nanomaterials have been introduced as emerging technologies to respond to some of the aforementioned challenges. For example, iron and copper nanoparticles (NPs) have been utilized as plant micronutrients. Therefore, due to their success as antifungal and antibacterial, silver NPs have been applied to control phytopathogens and extend the vase life of some flowers [2]. Metallic NPs have also been used as nano-pesticides to increase the dispersion and wettability of agricul-

Besides the above mentioned, while some metallic NPs may have positive effects upon plant systems, it is also possible that this class of NPs has negative implications for plant systems. For instance, barriers to growth for plant systems may occur, negative impact soil microbial structure or function, directly or indirectly alter the formation of symbiotic associations with root fungi and bacteria, influencing nutri-

A nanomaterial gaining popularity is zinc oxide (ZnO), the third metal-containing nanomaterial most commonly used [4–6]. The ZnO nanoparticle is considered multifunctional because it has high chemical stability, wide ultraviolet radiation absorption range and high photostability, and antifungal activity. Such properties allow this nanoparticle to be used to manufacture clothes with ultraviolet (UV) filters, sunscreens, baby rash ointments, paints, and even as food preservatives [7]. The ZnO NPs wide spectrum of applications makes it susceptible to entering the environment through various paths, such as effluents, spillage during transport, handling, direct contact through topical and oral consumer products, and incorrect disposal [8]. Such factors lead to contamination of environments and consequently adverse effects for humans and animals, such as excessive induction of reactive species, which can cause oxidative stress and trigger a cascade of damage in macromolecules, genotoxicity, apoptosis, neurotoxicity, and negative implications for embryonic development [9, 10]. We have shown that amorphous zinc oxide nanoparticles have greater genotoxicity than crystalline (nanocrystals - NCs) [11]. Besides, we have demonstrated its biocompatibility through intraosseous implants [12]. However, the search for nanomaterials with hybrid properties has been stand-

Doping is a technique that makes it possible to incorporate substitutional ions into the crystalline structure of materials, generating exciting properties [13]. The transition metals are elements whose corresponding atoms do not have a more energetic "d" orbital filled or capable of forming cations with an incomplete d orbital. Therefore, the incorporation of these metals in nanocrystals makes it possible to mix properties, such as magneto-optics [refs]. In addition to this property, other properties are observed, some of which we will show in this chapter. In particular, we will show results of pure ZnO nanocrystals and doped with transition metals and that depend-

Depending on the doping ion, the nanoparticles' toxicity may be reduced [14]. Copper (Cu) is one of the transition metals with the lowest toxicity to humans, which allows its application in medicine when used in intrauterine devices, and its antibacterial activity [14, 15]. Thus, in the present work, the ZnO NCs were doped with the copper transition metal (Cu doped ZnO) and reduction of toxicity due to doping. To evaluate the biocompatibility of this new nanoparticle, we analyzed the development of the fruit fly (*Drosophila melanogaster*) in a medium containing ZnO

*Drosophila melanogaster*, known as fruit fly, is a well-established model organism in several areas of science, including nanotoxicology [16]. It offers several mutant lines for a broad range of human diseases, has low cost and easy maintenance in the laboratory, and a short life cycle compared to other model organisms such as mammals and fish. These features make the fruit fly a great model for studies

ing on the dopant, specific properties may or not be improved.

**84**

or Cu doped ZnO.

#### **Figure 1.**

*(a) Illustrative scheme of the crystalline structure of ZnO and the substitutional incorporation of iron (Fe) ions in the nanocrystal. (b) Reduction of absorbance over time in reactions using Fe-doped ZnO in different proportions for malachite green degradation.*

In this topic we present the toxicity analysis of pure and copper (Cu) doped ZnO NCs at a concentration of 0.25 mg/mL on the development of Drosophila larvae. **Figure 2(a)** shows the Illustrative scheme of ZnO's crystalline structure and the substitutional incorporation of Cu ions in the nanocrystal. The results of the pupation rate following ZnO and Cu doped ZnO NCs exposure are shown in **Figure 2(b)**. As observed, there was a one-day delay in the time the larvae took to reach the pupal stage when exposed to Cu doped ZnO when compared to control and ZnO NCs (**Figure 2(c)**). Additionally, all the viable ZnO NCs treated animals were able to reach the puparium on the third day, while in the control samples, pupae formation was observed until the fifth day. Interestingly, most of the Cu doped ZnO NCs animals also reached the pupal stage on the fifth day. However, we could still observe pupae being formed until the eighth day. Delays in larval development were also evaluated in experiments carried out with Drosophila larvae that developed in medium containing silver (Ag) nanocrystals [26] or Cu on a nano or micrometric scale [27, 28]. In addition to the development delay analysis, we also observed the rate of larval lethality of the treated animals. The larvae developed at 0.25 mg/mL ZnO NCs showed the highest mortality rate when compared to control. Surprisingly, when ZnO NCs was copper doped (Cu doped ZnO) it reduced the

**87**

**Figure 2.**

*Transition Metals Doped Nanocrystals: Synthesis, Characterization, and Applications*

larval lethality by 12.5% compared to ZnO NCs, suggesting that copper doping was able to increase the ZnO NCs biocompatibility in vivo by decreasing its toxicity.

*(a) Illustrative scheme of the crystalline structure of ZnO and the substitutional incorporation of Cu in the ZnO nanocrystal. The effects of ZnO and Cu doped ZnO NCs during the larval development of Drosophila. (b) Rate of daily pupal formation in animals treated with 0.25 mg/mL of ZnO or Cu doped ZnO. (c) Larval lethality rate after development in standard culture medium added with ZnO or Cu doped ZnO NCs. (n = 6;* 

*35 larvae per replicate). abc indicates a statistical difference between treatments.*

**1.3 Chrome-doped Bi2S3 nanocrystals embedded in host glass matrix**

Diluted magnetic semiconductors (DMS) embedded in a glassy matrix, such as: Bi2-xMnxS3 [32], Bi2-xFexS3, [33] Bi2-xCoxS3 [34] and Bi2-xCrxS3, [35] have potential properties for the production of photovoltaic cells [36, 37] thermoelectric cooling, [38, 39] photodetectors, [40] field emission electronics [41] and fluorescent markers [42]. Bi2S3 (bulk) has an orthorhombic crystalline structure, [43] exciton Bohr radius of 24 nm [44], and bandgap of 1.3 eV [45]. The nature of the Cr S bond in Bi2S3 NCs

Developmental delays and lethality can be triggered by the formation of reactive species that cause redox imbalance and lead to cell damage, such as the oxidation of proteins, lipids, and DNA [9]. The redox imbalance leads to changes in the synthesis of antioxidants such as catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), and the total glutathione (GSH) protein [29]. Total glutathione plays a crucial role in the synthesis of other antioxidant enzymes, such as GST, and is also involved in the ecdysone biosynthesis mechanism. Ecdysone plays various roles in the regulation of many developmental and physiological processes, especially molting and metamorphosis [30, 31]. Our data showed a high lethality and delay in larval development, which can be explained by the production of reactive species that initiate cellular damage and the imbalance of antioxidant enzymes. The imbalance in the synthesis of antioxidant enzymes, including GST, could lead to larval lethality and impair the ecdysone biosynthesis causing larval development problems. The decrease in larval lethality observed for Cu doped ZnO NCs compared to ZnO NCs could be explained by a lower effect on the level of antioxidant enzymes, suggesting that the transition metal copper was sufficient to increase ZnO NCs biocompatibility in vivo. However, additional studies are crucial to better understand the mechanisms by which development is influenced by nanocrystals.

*DOI: http://dx.doi.org/10.5772/intechopen.97326*

*Transition Metals Doped Nanocrystals: Synthesis, Characterization, and Applications DOI: http://dx.doi.org/10.5772/intechopen.97326*

#### **Figure 2.**

*Transition Metal Compounds - Synthesis, Properties, and Application*

In this topic we present the toxicity analysis of pure and copper (Cu) doped ZnO NCs at a concentration of 0.25 mg/mL on the development of Drosophila larvae. **Figure 2(a)** shows the Illustrative scheme of ZnO's crystalline structure and the substitutional incorporation of Cu ions in the nanocrystal. The results of the pupation rate following ZnO and Cu doped ZnO NCs exposure are shown in **Figure 2(b)**. As observed, there was a one-day delay in the time the larvae took to reach the pupal stage when exposed to Cu doped ZnO when compared to control and ZnO NCs (**Figure 2(c)**). Additionally, all the viable ZnO NCs treated animals were able to reach the puparium on the third day, while in the control samples, pupae formation was observed until the fifth day. Interestingly, most of the Cu doped ZnO NCs animals also reached the pupal stage on the fifth day. However, we could still observe pupae being formed until the eighth day. Delays in larval development were also evaluated in experiments carried out with Drosophila larvae that developed in medium containing silver (Ag) nanocrystals [26] or Cu on a nano or micrometric scale [27, 28]. In addition to the development delay analysis, we also observed the rate of larval lethality of the treated animals. The larvae developed at 0.25 mg/mL ZnO NCs showed the highest mortality rate when compared to control. Surprisingly, when ZnO NCs was copper doped (Cu doped ZnO) it reduced the

*(a) Illustrative scheme of the crystalline structure of ZnO and the substitutional incorporation of iron (Fe) ions in the nanocrystal. (b) Reduction of absorbance over time in reactions using Fe-doped ZnO in different* 

**86**

**Figure 1.**

*proportions for malachite green degradation.*

*(a) Illustrative scheme of the crystalline structure of ZnO and the substitutional incorporation of Cu in the ZnO nanocrystal. The effects of ZnO and Cu doped ZnO NCs during the larval development of Drosophila. (b) Rate of daily pupal formation in animals treated with 0.25 mg/mL of ZnO or Cu doped ZnO. (c) Larval lethality rate after development in standard culture medium added with ZnO or Cu doped ZnO NCs. (n = 6; 35 larvae per replicate). abc indicates a statistical difference between treatments.*

larval lethality by 12.5% compared to ZnO NCs, suggesting that copper doping was able to increase the ZnO NCs biocompatibility in vivo by decreasing its toxicity.

Developmental delays and lethality can be triggered by the formation of reactive species that cause redox imbalance and lead to cell damage, such as the oxidation of proteins, lipids, and DNA [9]. The redox imbalance leads to changes in the synthesis of antioxidants such as catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), and the total glutathione (GSH) protein [29]. Total glutathione plays a crucial role in the synthesis of other antioxidant enzymes, such as GST, and is also involved in the ecdysone biosynthesis mechanism. Ecdysone plays various roles in the regulation of many developmental and physiological processes, especially molting and metamorphosis [30, 31]. Our data showed a high lethality and delay in larval development, which can be explained by the production of reactive species that initiate cellular damage and the imbalance of antioxidant enzymes. The imbalance in the synthesis of antioxidant enzymes, including GST, could lead to larval lethality and impair the ecdysone biosynthesis causing larval development problems. The decrease in larval lethality observed for Cu doped ZnO NCs compared to ZnO NCs could be explained by a lower effect on the level of antioxidant enzymes, suggesting that the transition metal copper was sufficient to increase ZnO NCs biocompatibility in vivo. However, additional studies are crucial to better understand the mechanisms by which development is influenced by nanocrystals.

#### **1.3 Chrome-doped Bi2S3 nanocrystals embedded in host glass matrix**

Diluted magnetic semiconductors (DMS) embedded in a glassy matrix, such as: Bi2-xMnxS3 [32], Bi2-xFexS3, [33] Bi2-xCoxS3 [34] and Bi2-xCrxS3, [35] have potential properties for the production of photovoltaic cells [36, 37] thermoelectric cooling, [38, 39] photodetectors, [40] field emission electronics [41] and fluorescent markers [42].

Bi2S3 (bulk) has an orthorhombic crystalline structure, [43] exciton Bohr radius of 24 nm [44], and bandgap of 1.3 eV [45]. The nature of the Cr S bond in Bi2S3 NCs doped with Cr ions can lead to physical properties dependent on the spin dynamics, associated with the effects of quantum confinement of size, concentration control, and coordination site of the doping ions. As the Cr ions enter the Bi2S3 structure, replacing the Bi3+ ions, most likely with 3d3 valence and 3/2 spin configurations, consequently, it becomes possible to add magnetic properties to the Bi2S3 non-magnetic NCs. The smaller ionic radius of Cr3+ (0.53 Å) to Bi3+ (1.03 Å) facilitates occupy vacancies in the Bi2S3 orthorhombic network [35, 46]. According to the theories of the crystal and ligand field, the energy states of the free Cr3+ ions will depend strongly on the interaction intensity of the chalcogenide ion (S2−) environment that defines the crystal symmetry [34, 35, 46].

In this context, the role of x concentration of Cr ions in Bi2-xCrxS3 NCs incorporated in glassy systems, which derive from the control of charge carriers in the semiconductor energy bands, through the magnetic saturation of Cr3+ ions, was investigated to manipulate the properties of this new material.

**Figure 3(a)** shows the UV–VIS optical absorption spectra (OA) of Bi2-xCrxS3 NCs incorporated in SNAB glass matrix, at temperature (300 K), as a function of the increasing concentration of doping xCr ions (x = 0.00; 0.050; 0.100). The OA spectrum of the SNAB matrix (black line) appears at the bottom of **Figure 3(a)**. Throughout the spectral range, there is no band signal associated with the absorption of Bi2-xCrxS3 NCs. In comparison with the Bi2S3 NCs of the intrinsic semiconductor (x = 0.00), the OA spectra of the Bi2-xCrxS3 NCs underwent changes due to the doping of chromium ions in the symmetrical environment of

#### **Figure 3.**

*(a) Optical absorption spectra at room temperature of Bi2-xCrxS3 NCs (x = 0.00; 0.050 and 0.100) incorporated in the SNAB glass matrix annealed for 2 h at 500° C. For comparison purposes, the absorption spectrum of the SNAB glass matrix is represented on the black bottom line. The insert shows the energy level diagram for Cr3+ (3d3 ) at an octahedral site and the respective transitions allowed and prohibited by spin. (b) Bi2S3 orthorhombic unit cell and quantum dots with the interstitial replacement of Bi3 + ions by Cr3+ at distorted octahedral sites. (c) TEM images of Bi2-xCrxS3 NCs (x = 0.10). (d) XRD diffractograms at room temperature of Bi2-xCrxS3 NCs embedded in the SNAB glass matrix. The insertion shows a comparison between peaks (210) with increasing concentration x.*

**89**

ation method.

*Transition Metals Doped Nanocrystals: Synthesis, Characterization, and Applications*

the NCs structure. The intensities of the electronic transition bands increased due to the increasing concentration of Cr3+ ions. Therefore, the OA spectra show energy bands of the components of the excitonic states and of the Cr3+ ions in the

ions correspond to the spin allowed and forbidden d-d transitions. The results presented in **Figure 3(a)** are evidence of the incorporation of Cr3+ions in a ligand

**Figure 3(a)**, are assigned the spin allowed and forbidden transitions <sup>4</sup>

A2 (4

G) (1,86 eV), 4

F) → <sup>4</sup>

Therefore, the excited states of the coordination crystal field [CrS6]

According to the crystal field theory, the identified bands attributed to the Cr3+

structure of Bi2S3, since the positions of these energies, are specific to this particular site [35, 46] **Figure 3(b)** shows the unit cell with orthorhombic structure and the Bi2-xCrxS3 NCs with interstitial doping Cr3+ ions in a distorted octahedral symmetry. The bands identified in the spectral range of the visible in the OA spectra of

T1 (4

a consequence of the strength of the crystal field (∆ = 15877 cm−1) and the Racah parameter of interelectronic repulsion (B = 665 cm−1), based on the Tanabe-Sugano

located within the energy band gap (2.95 eV) of the absorption associated with the excitonic transition of the Bi2-xCrxS3 NCs. The blueshift observed at the OA band edge for the Bi2-xCrxS3 NCs (2.95 eV) in relation to the corresponding intrinsic semiconductor (2.86 eV), results in sp-d exchange interactions between electrons confined in states of quantum dots and localized states partially filled with Cr3+ ions. The quantum size of the Bi2-xCrxS3 NCs does not change with the increase of Cr incorporation in the samples. **Figure 3(b)** shows an illustration of the Bi2-xCrxS3 NCs with quantum dot properties as a function of the x concentration of Cr3+ ions at

Bi2-xCrxS3 NCs (x = 0.10) embedded in SNAB glass matrix with an average size of 10 nm are shown in the TEM image of **Figure 3(c)**. The distance d210 = 0.325 nm attributed to the crystal plane (210), shows the preserved orthorhombic structure for NCs Bi2S3. The X-ray diffraction measurements for Bi2-xCrxS3 NCs (x = 0.00 and 0.05) confirm the standard peaks of the orthorhombic crystal system of the bismuthinite mineral (RRUFF ID: R070533.9). In the inset of **Figure 3(d)**, a shift to smaller angles (2θ) of the diffraction peak (210) is shown, as the Cr concentration increases from x = 0.00 to x = 0.05. The shift in the diffraction peak caused by a change in the lattice constant due to the substitute Bi3+ ions by Cr3+ in the orthorhombic crystal structure of Bi2S3. The intensity of the XRD peaks increases with the xCr concentration. However, the structure preserved due to the non-saturation

The incorporation of transition metal ions into wide energy gap semiconductors, as ZnTe (Eg = 2.26 eV), [47] creates intermediate energy states between the valence and conduction bands in these host semiconductors, [48] allowing the manipulation of their magnetic and optical properties, [49] which in turn governs sp–d spin interaction between carriers and magnetic ions. Although Ni-doped ZnTe NCs are currently synthesized in various methods, [50, 51] some possible applications require nanoparticles to be embedded in highly stable, robust, and transparent host materials, as the glass systems. In this context, we present a very effective method for the growth of Ni2+ ion-doped ZnTe NCs in a glass system using the fusion nucle-

A2g (4

F) → <sup>4</sup>

T2g (4

F) (2,82 eV). Such energy states are

−9) of the orthorhombic

A2( 4 F) → <sup>2</sup> Eg

−9 are

A2g

F) (1,94 eV), 4

*DOI: http://dx.doi.org/10.5772/intechopen.97326*

field of S2− ions in octahedral coordination sites ([CrS6]

T1( 2

octahedral (Oh) for C/B = 4.5 [46].

of the Cr doping concentration in the Bi2-xCrxS3 NCs.

**1.4 Nickel-doped ZnTe nanocrystals embedded in host glass matrix**

Bi2-xCrxS3 NCs.

G) (1,79 eV), 4

diagram d3

octahedral sites.

T2g (2

A2( 4 F) → <sup>2</sup>

G) (2,59 eV), e 4

( 2

( 4 F) → <sup>2</sup> *Transition Metals Doped Nanocrystals: Synthesis, Characterization, and Applications DOI: http://dx.doi.org/10.5772/intechopen.97326*

the NCs structure. The intensities of the electronic transition bands increased due to the increasing concentration of Cr3+ ions. Therefore, the OA spectra show energy bands of the components of the excitonic states and of the Cr3+ ions in the Bi2-xCrxS3 NCs.

According to the crystal field theory, the identified bands attributed to the Cr3+ ions correspond to the spin allowed and forbidden d-d transitions. The results presented in **Figure 3(a)** are evidence of the incorporation of Cr3+ions in a ligand field of S2− ions in octahedral coordination sites ([CrS6] −9) of the orthorhombic structure of Bi2S3, since the positions of these energies, are specific to this particular site [35, 46] **Figure 3(b)** shows the unit cell with orthorhombic structure and the Bi2-xCrxS3 NCs with interstitial doping Cr3+ ions in a distorted octahedral symmetry. The bands identified in the spectral range of the visible in the OA spectra of **Figure 3(a)**, are assigned the spin allowed and forbidden transitions <sup>4</sup> A2( 4 F) → <sup>2</sup> Eg ( 2 G) (1,79 eV), 4 A2( 4 F) → <sup>2</sup> T1( 2 G) (1,86 eV), <sup>4</sup> A2g (4 F) → <sup>4</sup> T2g (4 F) (1,94 eV), 4 A2g ( 4 F) → <sup>2</sup> T2g (2 G) (2,59 eV), e <sup>4</sup> A2 (4 F) → <sup>4</sup> T1 (4 F) (2,82 eV). Such energy states are a consequence of the strength of the crystal field (∆ = 15877 cm−1) and the Racah parameter of interelectronic repulsion (B = 665 cm−1), based on the Tanabe-Sugano diagram d3 octahedral (Oh) for C/B = 4.5 [46].

Therefore, the excited states of the coordination crystal field [CrS6] −9 are located within the energy band gap (2.95 eV) of the absorption associated with the excitonic transition of the Bi2-xCrxS3 NCs. The blueshift observed at the OA band edge for the Bi2-xCrxS3 NCs (2.95 eV) in relation to the corresponding intrinsic semiconductor (2.86 eV), results in sp-d exchange interactions between electrons confined in states of quantum dots and localized states partially filled with Cr3+ ions. The quantum size of the Bi2-xCrxS3 NCs does not change with the increase of Cr incorporation in the samples. **Figure 3(b)** shows an illustration of the Bi2-xCrxS3 NCs with quantum dot properties as a function of the x concentration of Cr3+ ions at octahedral sites.

Bi2-xCrxS3 NCs (x = 0.10) embedded in SNAB glass matrix with an average size of 10 nm are shown in the TEM image of **Figure 3(c)**. The distance d210 = 0.325 nm attributed to the crystal plane (210), shows the preserved orthorhombic structure for NCs Bi2S3. The X-ray diffraction measurements for Bi2-xCrxS3 NCs (x = 0.00 and 0.05) confirm the standard peaks of the orthorhombic crystal system of the bismuthinite mineral (RRUFF ID: R070533.9). In the inset of **Figure 3(d)**, a shift to smaller angles (2θ) of the diffraction peak (210) is shown, as the Cr concentration increases from x = 0.00 to x = 0.05. The shift in the diffraction peak caused by a change in the lattice constant due to the substitute Bi3+ ions by Cr3+ in the orthorhombic crystal structure of Bi2S3. The intensity of the XRD peaks increases with the xCr concentration. However, the structure preserved due to the non-saturation of the Cr doping concentration in the Bi2-xCrxS3 NCs.

#### **1.4 Nickel-doped ZnTe nanocrystals embedded in host glass matrix**

The incorporation of transition metal ions into wide energy gap semiconductors, as ZnTe (Eg = 2.26 eV), [47] creates intermediate energy states between the valence and conduction bands in these host semiconductors, [48] allowing the manipulation of their magnetic and optical properties, [49] which in turn governs sp–d spin interaction between carriers and magnetic ions. Although Ni-doped ZnTe NCs are currently synthesized in various methods, [50, 51] some possible applications require nanoparticles to be embedded in highly stable, robust, and transparent host materials, as the glass systems. In this context, we present a very effective method for the growth of Ni2+ ion-doped ZnTe NCs in a glass system using the fusion nucleation method.

*Transition Metal Compounds - Synthesis, Properties, and Application*

investigated to manipulate the properties of this new material.

the Bi3+ ions, most likely with 3d3

symmetry [34, 35, 46].

doped with Cr ions can lead to physical properties dependent on the spin dynamics, associated with the effects of quantum confinement of size, concentration control, and coordination site of the doping ions. As the Cr ions enter the Bi2S3 structure, replacing

it becomes possible to add magnetic properties to the Bi2S3 non-magnetic NCs. The smaller ionic radius of Cr3+ (0.53 Å) to Bi3+ (1.03 Å) facilitates occupy vacancies in the Bi2S3 orthorhombic network [35, 46]. According to the theories of the crystal and ligand field, the energy states of the free Cr3+ ions will depend strongly on the interaction intensity of the chalcogenide ion (S2−) environment that defines the crystal

In this context, the role of x concentration of Cr ions in Bi2-xCrxS3 NCs incorporated in glassy systems, which derive from the control of charge carriers in the semiconductor energy bands, through the magnetic saturation of Cr3+ ions, was

**Figure 3(a)** shows the UV–VIS optical absorption spectra (OA) of Bi2-xCrxS3 NCs incorporated in SNAB glass matrix, at temperature (300 K), as a function of the increasing concentration of doping xCr ions (x = 0.00; 0.050; 0.100). The OA spectrum of the SNAB matrix (black line) appears at the bottom of **Figure 3(a)**. Throughout the spectral range, there is no band signal associated with the absorption of Bi2-xCrxS3 NCs. In comparison with the Bi2S3 NCs of the intrinsic semiconductor (x = 0.00), the OA spectra of the Bi2-xCrxS3 NCs underwent changes due to the doping of chromium ions in the symmetrical environment of

*(a) Optical absorption spectra at room temperature of Bi2-xCrxS3 NCs (x = 0.00; 0.050 and 0.100) incorporated in the SNAB glass matrix annealed for 2 h at 500° C. For comparison purposes, the absorption spectrum of the SNAB glass matrix is represented on the black bottom line. The insert shows the energy level diagram* 

*orthorhombic unit cell and quantum dots with the interstitial replacement of Bi3 + ions by Cr3+ at distorted octahedral sites. (c) TEM images of Bi2-xCrxS3 NCs (x = 0.10). (d) XRD diffractograms at room temperature of Bi2-xCrxS3 NCs embedded in the SNAB glass matrix. The insertion shows a comparison between peaks (210)* 

*) at an octahedral site and the respective transitions allowed and prohibited by spin. (b) Bi2S3*

valence and 3/2 spin configurations, consequently,

**88**

**Figure 3.**

*for Cr3+ (3d3*

*with increasing concentration x.*

**Figure 4** presents optical absorption (OA) spectra in the range of 250 nm - 1800 nm (a) and EPR spectra (b), of samples containing Zn1-xNixTe NCs, with Ni-concentrations ranging from x = 0.000 to x = 0.100.

Already the **Figure 4(c)** shows TEM images of glass samples cntaining Zn1-xNixTe NCs, with concentrations x = 0.00 and x = 0.05. Optical absorption spectra confirm the substitutional incorporation of Ni2+ ions in the ZnTe semiconductor lattice due to the absorption bands Ni2+ ion and the redshift from 3.10 eV (400 nm) to 2.85 eV (435 nm), when x ranges from 0.00 to 0.10. This redshift is related to the sp-d exchange interaction between the d band localized electrons of the Ni2+ transition

#### **Figure 4.**

*(a) Optical absorption (b) EPR spectra of samples containing Zn1-xNixTe NCs, with Ni-concentrations ranging from x = 0.000 to x = 0.100. In (c) TEM images for concentrations x = 0.00 and x = 0.05.*

**91**

*Transition Metals Doped Nanocrystals: Synthesis, Characterization, and Applications*

metal ions and the sp. sub-levels electrons of the ZnTe host semiconductor, with increasing Ni concentration [51]. Transmission electronic microscopy (TEM) images were used to determine the NCs sizes, exhibiting quantum dots and bulk morphologies. It also revealed that the lattice parameter was not affected by higher concentrations of Ni doping Ni2+ and Zn2+ have very similar ionic radii. Electron paramagnetic resonance spectra display resonance lines that confirm the substitutional incorporation (g = 2.0991) and also the presence of Ni2+ ions at vacancy sites (g ≈ 2.0023) of the

Therefore, a more extensive investigation of the properties of ZnTe structures doped with Ni2+ ions could lead to novel technological applications in spintronic devices, as a magnetic field acting on the spin of the unpaired electrons would allow

**1.5 Manganese-doped CdTe nanocrystals embedded in host glass matrix**

particular on Cadmium Telluride (CdTe) doped with Mn2+ ions [58, 59].

Cadmium chalcogenides doped with small amounts of magnetic impurities, such as manganese (Mn2+) ions, called diluted magnetic semiconductors (DMS), have been extensively studied due to their significant magneto-optical properties [54–57]. In view of these interesting properties, In this section, we will comment in

**Figure 5(a)** shows the optical absorption (OA) bands of CdTe ultra-small quantum dots (USQDs). As the concentration increases, there is a blueshift with an increase in magnetic doping, as indicated by the arrows: 2.87 eV (x = 0.005); 2.90 eV (x = 0.010); 2.92 eV (x = 0.050) and 2.94 eV (x = 0.100 [60]. The blueshift provides strong evidence that Mn2 + ions have actually been incorporated into the CdTe USQDs, which will be confirmed by the Electronic Paramagnetic Resonance

The confirmation of the formation of the USQDs and the size distribution is confirmed in Atomic Force Microscopy (AFM) images, shown in **Figure 5(b)** and **(c)**. It is observed in the histograms of the topographic images that there was no relative change in the mean radius of the USQDs with the increase in manganese concentration. In the luminescence spectra, **Figure 5(d)**, it is observed that with the increase in the concentration of manganese, there is an increase in the intensities of the emission bands centered around 564 nm (2.19 eV) and 617 nm (2.01 eV), attributed, respectively, to the levels of surface defects (ESDL) and Mn2 + ions (EMn2 +). In addition, there is a decrease in the intensity of emissions related to vacancies E1 and E2, located around 753 nm (1.65 eV) and 892 nm (1.39 eV). EMn2 + emission occurs

Mn2+ ions can be substitutionally incorporated at two different sites: one in the nucleus (named as SI) [62] and another near the surface of the USQDs (named as SII) [58]. This emission (EMn2+) is suppressed when the Mn2+ ions are incorporated into the USQDs' SII site [61]. Thus, the presence of EMn2 + emission for higher concentrations of manganese confirms that Mn2 + ions are also incorporated in SI. On the other hand, the decrease in E1 and E2 emissions with the increase in manganese concentration shows that Mn2 + ions are replacing vacancies in Cd1-xMnxTe USQDs. All of these emis-

In the EPR spectra of the doped samples, the presence of the six lines is observed, which confirms that the Mn2 + ions are incorporated in the crystalline structure of the CdTe USQDs, replacing the Cd2 + sites, confirming that the grown structures are Cd1-xMnxTe USQDs (**Figure 5(f )**) [58]. The increase in the concentration of Mn2+ ions causes an increase in the intensity of the bottom lines. This effect is attributed to the dipole interactions between Mn-Mn. **Figure 5(g)** shows

A1, which is characteristic of the d orbital of Mn2+ ions when

simultaneous use of spin, electronic and optical properties.

*DOI: http://dx.doi.org/10.5772/intechopen.97326*

ZnTe lattice [52, 53].

(EPR) spectra.

between levels 4

T1 → <sup>6</sup>

substitutionally incorporated in semiconductors II-VI [61].

sions are represented in the energy diagram in **Figure 5(e)**.

#### *Transition Metals Doped Nanocrystals: Synthesis, Characterization, and Applications DOI: http://dx.doi.org/10.5772/intechopen.97326*

metal ions and the sp. sub-levels electrons of the ZnTe host semiconductor, with increasing Ni concentration [51]. Transmission electronic microscopy (TEM) images were used to determine the NCs sizes, exhibiting quantum dots and bulk morphologies. It also revealed that the lattice parameter was not affected by higher concentrations of Ni doping Ni2+ and Zn2+ have very similar ionic radii. Electron paramagnetic resonance spectra display resonance lines that confirm the substitutional incorporation (g = 2.0991) and also the presence of Ni2+ ions at vacancy sites (g ≈ 2.0023) of the ZnTe lattice [52, 53].

Therefore, a more extensive investigation of the properties of ZnTe structures doped with Ni2+ ions could lead to novel technological applications in spintronic devices, as a magnetic field acting on the spin of the unpaired electrons would allow simultaneous use of spin, electronic and optical properties.

#### **1.5 Manganese-doped CdTe nanocrystals embedded in host glass matrix**

Cadmium chalcogenides doped with small amounts of magnetic impurities, such as manganese (Mn2+) ions, called diluted magnetic semiconductors (DMS), have been extensively studied due to their significant magneto-optical properties [54–57]. In view of these interesting properties, In this section, we will comment in particular on Cadmium Telluride (CdTe) doped with Mn2+ ions [58, 59].

**Figure 5(a)** shows the optical absorption (OA) bands of CdTe ultra-small quantum dots (USQDs). As the concentration increases, there is a blueshift with an increase in magnetic doping, as indicated by the arrows: 2.87 eV (x = 0.005); 2.90 eV (x = 0.010); 2.92 eV (x = 0.050) and 2.94 eV (x = 0.100 [60]. The blueshift provides strong evidence that Mn2 + ions have actually been incorporated into the CdTe USQDs, which will be confirmed by the Electronic Paramagnetic Resonance (EPR) spectra.

The confirmation of the formation of the USQDs and the size distribution is confirmed in Atomic Force Microscopy (AFM) images, shown in **Figure 5(b)** and **(c)**. It is observed in the histograms of the topographic images that there was no relative change in the mean radius of the USQDs with the increase in manganese concentration.

In the luminescence spectra, **Figure 5(d)**, it is observed that with the increase in the concentration of manganese, there is an increase in the intensities of the emission bands centered around 564 nm (2.19 eV) and 617 nm (2.01 eV), attributed, respectively, to the levels of surface defects (ESDL) and Mn2 + ions (EMn2 +). In addition, there is a decrease in the intensity of emissions related to vacancies E1 and E2, located around 753 nm (1.65 eV) and 892 nm (1.39 eV). EMn2 + emission occurs between levels 4 T1 → <sup>6</sup> A1, which is characteristic of the d orbital of Mn2+ ions when substitutionally incorporated in semiconductors II-VI [61].

Mn2+ ions can be substitutionally incorporated at two different sites: one in the nucleus (named as SI) [62] and another near the surface of the USQDs (named as SII) [58]. This emission (EMn2+) is suppressed when the Mn2+ ions are incorporated into the USQDs' SII site [61]. Thus, the presence of EMn2 + emission for higher concentrations of manganese confirms that Mn2 + ions are also incorporated in SI. On the other hand, the decrease in E1 and E2 emissions with the increase in manganese concentration shows that Mn2 + ions are replacing vacancies in Cd1-xMnxTe USQDs. All of these emissions are represented in the energy diagram in **Figure 5(e)**.

In the EPR spectra of the doped samples, the presence of the six lines is observed, which confirms that the Mn2 + ions are incorporated in the crystalline structure of the CdTe USQDs, replacing the Cd2 + sites, confirming that the grown structures are Cd1-xMnxTe USQDs (**Figure 5(f )**) [58]. The increase in the concentration of Mn2+ ions causes an increase in the intensity of the bottom lines. This effect is attributed to the dipole interactions between Mn-Mn. **Figure 5(g)** shows

*Transition Metal Compounds - Synthesis, Properties, and Application*

ranging from x = 0.000 to x = 0.100.

**Figure 4** presents optical absorption (OA) spectra in the range of 250 nm - 1800 nm (a) and EPR spectra (b), of samples containing Zn1-xNixTe NCs, with Ni-concentrations

Already the **Figure 4(c)** shows TEM images of glass samples cntaining Zn1-xNixTe NCs, with concentrations x = 0.00 and x = 0.05. Optical absorption spectra confirm the substitutional incorporation of Ni2+ ions in the ZnTe semiconductor lattice due to the absorption bands Ni2+ ion and the redshift from 3.10 eV (400 nm) to 2.85 eV (435 nm), when x ranges from 0.00 to 0.10. This redshift is related to the sp-d exchange interaction between the d band localized electrons of the Ni2+ transition

*(a) Optical absorption (b) EPR spectra of samples containing Zn1-xNixTe NCs, with Ni-concentrations ranging from x = 0.000 to x = 0.100. In (c) TEM images for concentrations x = 0.00 and x = 0.05.*

**90**

**Figure 4.**

#### **Figure 5.**

*(a) Optical absorption spectra (b, c) AFM images, (d) Luminescence spectra, (e) Energy Diagram (f) EPR spectra, (g) Mn2+ ions Concentration of samples containing Cd1-xMnxTe UPNCs, with Mn-concentrations ranging from x = 0.000 to x = 0.100.*

the estimate of the relative concentrations of Mn2 + ions for samples containing Cd1-xMnxTe USQDs with x = 0.010, 0.050 and 0.100. It is observed that the increase in the concentration of manganese results in an increase in the concentration of Mn2+ ions inserted in the CdTe USQDs. Therefore, these results confirm the growth of Cd1-xMnxTe USQDs.

#### **2. Conclusion**

Therefore, this chapter shows how the incorporation of transition metals in nanocrystals can change their physical, chemical, and biological properties. In addition, depending on the application, these nanocrystals may be in powder or host glass systems. Interestingly, the doping with iron ions in the ZnO NCs did not change for malachite green degradation in relation of ZnO NCs. However, the doping with copper ions in ZnO NCs improved in the biocompatibility of ZnO NCs. Regarding physical properties, the incorporation of transition metals in semiconductors, allows the emergence of the magneto-optical properties as shown in nanocrystals doped with manganese, chromium or nickel ions, and their manipulation depend on the concentration and heat treatment when embedded in glass matrices.

**93**

*Transition Metals Doped Nanocrystals: Synthesis, Characterization, and Applications*

This work was supported by grants of CNPq, CAPES, and FAPEMIG.

, Luciana R.S. Floresta1,3,

, Éder V. Guimarães8

, Ricardo S. Silva8

,

, Karolina B. da Silva1,4,

, Vinícius P. Bittar1,6, Ana L.S. Borges1,6,

and Noelio O. Dantas1

, Alessandra S. Silva8

1 Laboratory of New Nanostructured and Functional Materials, Physics Institute,

2 Programa de Pós-Graduação da Rede Nordeste de Biotecnologia (RENORBIO),

5 Laboratory of Genetic and Applied Microbiology, Institute of Biological Sciences

6 Institute of Biotechnology, Federal University of Uberlândia, Uberlândia,

7 Physics Institute, Federal University of Uberlândia, Uberlândia, Minas Gerais,

8 Instituto de Ciências Exatas, Naturais e Educação (ICENE), Departamento de Física, Federal University of Triângulo Mineiro, Uberaba, Minas Gerais, Brazil

\*Address all correspondence to: acalmeida@fis.ufal.br and noelio@fis.ufal.br

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

3 Laboratory for in vivo Toxicity, Institute of Biological Sciences and Health,

4 Laboratory of Applied Electrochemistry, Institute of Chemistry and Biotechnology, Federal University of Alagoas, Maceió, Alagoas, Brazil

and Health, Federal University of Alagoas, Maceió, Alagoas, Brazil

, Lucas Anhezini3

Federal University of Alagoas, Maceió, Alagoas, Brazil

Federal University of Alagoas, Maceió, Alagoas, Brazil

Federal University of Alagoas, Maceió, Alagoas, Brazil

*DOI: http://dx.doi.org/10.5772/intechopen.97326*

**Acknowledgements**

**Conflict of interest**

Anielle C.A. Silva1,2\*, Jerusa M. de Oliveira3

The authors declare no conflict of interest.

Matheus V. da Silva1,4, José L. da S. Duarte4

**Author details**

Eurípedes A. da Silva Filho5

Guilherme L. Fernandes7

Carmem L.P.S. Zanta4

Minas Gerais, Brazil

provided the original work is properly cited.

Brazil

*Transition Metals Doped Nanocrystals: Synthesis, Characterization, and Applications DOI: http://dx.doi.org/10.5772/intechopen.97326*
