*2.1.5 Nanocrystals for the control plant bacterial disease*

To evaluate the growth inhibition zone of *Xanthomonas campestris pv. campestris in vitro,* a basic layer of 2% agar-water medium and semi-solid nutrient medium (0.8%)

with 10% of the bacterial suspension (108 CFU/mL) was added to Petri dishes. Seven disks of sterile filter paper (6 mm) were embedded with 10 μL of solution Ag-doped ZnO NCs, and Au-doped ZnO NCs, at 100; 10; 1; 0.1; and 0.01 mg/mL, and incubated at 28 °C for 48 hours. The diameter of the inhibition zone was measured.

In the greenhouse, tomato plants (three- to four-leaf stage) were sprayed with Mg-doped ZnO NCs at 2.5 mg/mL, and three days later, the plants were inoculated with a *Xanthomonas gardneri*-bacterial suspension (109 CFU/mL). The severity of the disease was analyzed.

### *2.1.6 In vivo biocompatibility analysis in Drosophila melanogaster*

We have performed a developmental assay to evaluate whether Na2TiO7 and Na2TiO7:Ag could present any toxicity *in vivo*. Adult males and females were conditioned and kept in oviposition plates for six hours. After 24 hours of controlled oviposition, first instar larvae (L1) were carefully transferred (six replicates per concentration containing 30 larvae each) to standard *Drosophila* medium containing Na2TiO7 and Na2TiO7:Ag at the final concentration of 0.02 mg/mL (66.30 μmol/L) while control larvae were transferred to a standard culture medium. The animals developed through all larval stages during the following 4 days, while they actively fed until reaching the pupal stage. Animals that reached pupal stage were counted daily and it was possible to determine total pupation and daily pupation rate. We obtained the larval lethality rate by subtracting the number of pupae from the initial larvae number. After pupal metamorphosis, the animals emerge as adults and were transferred to a standard media and monitored throughout its adult lives to perform the adult lifespan assay. Deaths were counted daily until all animals were dead.

#### **2.2 Nanocrystals in powder: Development and applicability**

In this section, we will show the results of ZnO NCs doped with silver (Ag), gold (Au), and magnesium (Mg) ions to control bacterial diseases in agriculture. We will also present *in vivo* biocompatibility assays of pure and Ag-doped Na2Ti3O7 nanocrystals in *Drosophila* development.

## *2.2.1 Nanocrystals application in agriculture to control bacterial diseases*

The nanocrystals of ZnO in this work have a wurtzite structure, and silver (Ag), gold (Au), and magnesium (Mg) ions were doped in ZnO NCs, as shown in **Figure 1a**. The Ag or Au doped ZnO NCs inhibited *Xanthomonas campestris pv. camprestris* growth, at 100 and 10 mg/mL (**Figure 1b,c**). Other elements can also inhibit, such as, Mg ions that inhibited the growth of *Xanthomonas gardneri,* and reduced the severity of tomato bacterial spot (**Figure 1e**), and controlled the bacteria present in tomato seeds [31]. Therefore, nanotechnology could sustainably mitigate many challenges in disease management by reducing agrochemical use [32].

#### *2.2.2 Biocompatibility In Vivo of nanocrystals*

The crystalline structure of pure and silver (Ag) doped sodium titanate (Na2Ti3O7) is shown in **Figure 2a**. The Ag ions replace sodium (Na) or titanium (Ti) ions in sodium titanate's crystalline structure.

In order to investigate whether Na2Ti3O7 and Ag-doped Na2Ti3O7 nanocrystals could be biocompatible, we performed a bioassay to evaluate the effects of these NCs during *Drosophila* development. Surprisingly, the animals that developed

**145**

(**Figure 2b**).

**Figure 1.**

*Doped Semiconductor Nanocrystals: Development and Applications*

at Ag-doped Na2Ti3O7 NCs exhibit a lethality rate 12.8% lower when compared to animals that developed on Na2TiO7 NCs, suggesting that Ag doping was able to increase the Na2Ti3O7 NCs biocompatibility *in vivo* by decreasing its toxicity

*(a) Wurtzite structure of ZnO, Ag-doped ZnO, Au doped ZnO, and Mg-doped ZnO NCs. Growth inhibition zone for* Xanthomonas campestris pv. campestris *treated with (b) Ag-doped ZnO NCs and (c) Au doped ZnO NCs, at 100; 10; 1; 0.1; and 0.01 mg/mL. Strep. = streptomycin. Symptoms of bacterial spot-on tomato leaves, (d) caused by* Xanthomonas gardneri, *(e) with Mg-doped ZnO NCs showing disease control.*

As observed in **Figure 3a**, there was no delay in the time the larvae took to reach the pupal stage when exposed to Na2Ti3O7 and Ag-doped Na2Ti3O7 when compared to control. We have also performed an adult lifespan assay to evaluate the effects of NCs exposure during larval development and pupal metamorphosis over the adult survival. Therefore, after pupal metamorphosis, the animals that emerged as adults were immediately separated and kept in vials with standard control medium. These animals were transferred to a new vial with fresh standard medium every five days. The number of deaths for each experimental group was recorded daily until all individuals were dead. The lifetime of individuals that have developed in media

*DOI: http://dx.doi.org/10.5772/intechopen.96753*

*Doped Semiconductor Nanocrystals: Development and Applications DOI: http://dx.doi.org/10.5772/intechopen.96753*

#### **Figure 1.**

*Materials at the Nanoscale*

the disease was analyzed.

with 10% of the bacterial suspension (108

with a *Xanthomonas gardneri*-bacterial suspension (109

*2.1.6 In vivo biocompatibility analysis in Drosophila melanogaster*

**2.2 Nanocrystals in powder: Development and applicability**

*2.2.1 Nanocrystals application in agriculture to control bacterial diseases*

disease management by reducing agrochemical use [32].

*2.2.2 Biocompatibility In Vivo of nanocrystals*

ions in sodium titanate's crystalline structure.

crystals in *Drosophila* development.

CFU/mL) was added to Petri dishes. Seven

CFU/mL). The severity of

disks of sterile filter paper (6 mm) were embedded with 10 μL of solution Ag-doped ZnO NCs, and Au-doped ZnO NCs, at 100; 10; 1; 0.1; and 0.01 mg/mL, and incubated at 28 °C for 48 hours. The diameter of the inhibition zone was measured.

In the greenhouse, tomato plants (three- to four-leaf stage) were sprayed with Mg-doped ZnO NCs at 2.5 mg/mL, and three days later, the plants were inoculated

We have performed a developmental assay to evaluate whether Na2TiO7 and Na2TiO7:Ag could present any toxicity *in vivo*. Adult males and females were conditioned and kept in oviposition plates for six hours. After 24 hours of controlled oviposition, first instar larvae (L1) were carefully transferred (six replicates per concentration containing 30 larvae each) to standard *Drosophila* medium containing Na2TiO7 and Na2TiO7:Ag at the final concentration of 0.02 mg/mL (66.30 μmol/L) while control larvae were transferred to a standard culture medium. The animals developed through all larval stages during the following 4 days, while they actively fed until reaching the pupal stage. Animals that reached pupal stage were counted daily and it was possible to determine total pupation and daily pupation rate. We obtained the larval lethality rate by subtracting the number of pupae from the initial larvae number. After pupal metamorphosis, the animals emerge as adults and were transferred to a standard media and monitored throughout its adult lives to perform the adult lifespan assay. Deaths were counted daily until all animals were dead.

In this section, we will show the results of ZnO NCs doped with silver (Ag), gold (Au), and magnesium (Mg) ions to control bacterial diseases in agriculture. We will also present *in vivo* biocompatibility assays of pure and Ag-doped Na2Ti3O7 nano-

The nanocrystals of ZnO in this work have a wurtzite structure, and silver (Ag), gold (Au), and magnesium (Mg) ions were doped in ZnO NCs, as shown in **Figure 1a**. The Ag or Au doped ZnO NCs inhibited *Xanthomonas campestris pv. camprestris* growth, at 100 and 10 mg/mL (**Figure 1b,c**). Other elements can also inhibit, such as, Mg ions that inhibited the growth of *Xanthomonas gardneri,* and reduced the severity of tomato bacterial spot (**Figure 1e**), and controlled the bacteria present in tomato seeds [31]. Therefore, nanotechnology could sustainably mitigate many challenges in

The crystalline structure of pure and silver (Ag) doped sodium titanate (Na2Ti3O7) is shown in **Figure 2a**. The Ag ions replace sodium (Na) or titanium (Ti)

In order to investigate whether Na2Ti3O7 and Ag-doped Na2Ti3O7 nanocrystals could be biocompatible, we performed a bioassay to evaluate the effects of these NCs during *Drosophila* development. Surprisingly, the animals that developed

**144**

*(a) Wurtzite structure of ZnO, Ag-doped ZnO, Au doped ZnO, and Mg-doped ZnO NCs. Growth inhibition zone for* Xanthomonas campestris pv. campestris *treated with (b) Ag-doped ZnO NCs and (c) Au doped ZnO NCs, at 100; 10; 1; 0.1; and 0.01 mg/mL. Strep. = streptomycin. Symptoms of bacterial spot-on tomato leaves, (d) caused by* Xanthomonas gardneri, *(e) with Mg-doped ZnO NCs showing disease control.*

at Ag-doped Na2Ti3O7 NCs exhibit a lethality rate 12.8% lower when compared to animals that developed on Na2TiO7 NCs, suggesting that Ag doping was able to increase the Na2Ti3O7 NCs biocompatibility *in vivo* by decreasing its toxicity (**Figure 2b**).

As observed in **Figure 3a**, there was no delay in the time the larvae took to reach the pupal stage when exposed to Na2Ti3O7 and Ag-doped Na2Ti3O7 when compared to control. We have also performed an adult lifespan assay to evaluate the effects of NCs exposure during larval development and pupal metamorphosis over the adult survival. Therefore, after pupal metamorphosis, the animals that emerged as adults were immediately separated and kept in vials with standard control medium. These animals were transferred to a new vial with fresh standard medium every five days. The number of deaths for each experimental group was recorded daily until all individuals were dead. The lifetime of individuals that have developed in media

#### **Figure 2.**

*(a) Crystalline structure of pure and silver (Ag) doped sodium titanate (Na2Ti3O7). (b) Larval lethality following NCs exposure. As observed Na2Ti3O7 exposure caused a significant lethality rate during larval development, which was partially rescued by the Ag-doped Na2Ti3O7.*

containing Na2Ti3O7 and Ag-doped Na2Ti3O7 was compared to control animals that developed in a standard culture medium.

As shown in **Figure 3b** animals that developed in standard *Drosophila* medium containing Na2Ti3O7 showed 20 days decrease in lifespan when compared to control. Surprisingly, the emerged adult flies that developed in medium containing Ag-doped Na2Ti3O7 showed a longer longevity even when compared to animals that developed in standard culture medium or medium containing Na2Ti3O7 NCs. Therefore, our data suggests that Ag-doped Na2Ti3O7 was able to increase the Na2Ti3O7 NCs biocompatibility *in vivo* by decreasing its toxicity.

The toxicity of NCs, such as zinc oxide, titanium dioxide, magnetite, hydroxyapatite, and sodium titanate, is induced through the generation of reactive species and consequent oxidative stress [33–35]. The redox imbalance caused by NCs is capable of generating mitochondrial dysfunctions, inducing inflammatory responses, causing cytotoxicity and genotoxicity, in addition to altering the functioning of the sodium and potassium channels and consequent cell death [33]. Oxidative stress not only causes cell damage and protein oxidation but is also possibly responsible for altering the biosynthesis of hormones, such as ecdysone in insects. Ecdysone is a crucial hormone in the control of metamorphosis and ecdysis events in insects [36, 37]. Our data showed a high larval lethality, especially in animals exposed to Na2Ti3O7, possibly generated by oxidative stress, which can also impair ecdysone biosynthesis, causing developmental problems. One of the forgotten properties of NCs is their antioxidant capacity, such as Ag and cerium oxide

**147**

molecule [38].

*comparison to control animals.*

**Figure 3.**

*Doped Semiconductor Nanocrystals: Development and Applications*

nanoparticles (CONPs), and some NP of oxide that can even mimic an antioxidant

*(a) Daily pupation analysis of pure and Ag-doped Na2Ti3O7 exposed animals. It is possible to observe that the exposure to pure and Ag-doped Na2Ti3O7 Ag caused no delay in the transition from larva to pupa. (b) Lifespan analysis of pure and Ag-doped Na2Ti3O7 exposed animals. It is shown that Na2Ti3O7 exposure during development decreased adult longevity in about 20 days in comparison to control animals. However, the Ag-doped Na2Ti3O7 not only rescued the animals survival but surprisingly increased it in 10 days in* 

This section will show the results of Zn1-*x*CrxTe NCs, Zn1-*x*CuxTe NCs, and Bi2-x

**Figure 4** presents TEM images (**a**) and X-ray diffraction (XRD) (**b**) of samples

CrxTe3 NCs embedded in glass systems aiming at spintronics applications.

containing Zn1-*x*CrxTe NCs, with Cr-concentrations ranging from *x* = 0.00 to

*2.3.1 Cr- and Cu-doped ZnTe nanocrystals embedded in glass matrix*

Therefore, we believe that the reduction in larval lethality observed for Ag-doped Na2Ti3O7 NCs compared to Na2Ti3O7 NCs can be explained by a lesser effect on the generation of reactive species, suggesting that the transition metal silver was sufficient to increase the biocompatibility of Na2Ti3O7 NCs *in vivo*. However, additional studies are crucial to better understand the mechanisms by

which development is influenced by nanocrystals.

**2.3 Doped nanocrystals embedded in glass systems**

*DOI: http://dx.doi.org/10.5772/intechopen.96753*

*Doped Semiconductor Nanocrystals: Development and Applications DOI: http://dx.doi.org/10.5772/intechopen.96753*

#### **Figure 3.**

*Materials at the Nanoscale*

containing Na2Ti3O7 and Ag-doped Na2Ti3O7 was compared to control animals that

*(a) Crystalline structure of pure and silver (Ag) doped sodium titanate (Na2Ti3O7). (b) Larval lethality following NCs exposure. As observed Na2Ti3O7 exposure caused a significant lethality rate during larval* 

Na2Ti3O7 NCs biocompatibility *in vivo* by decreasing its toxicity.

As shown in **Figure 3b** animals that developed in standard *Drosophila* medium containing Na2Ti3O7 showed 20 days decrease in lifespan when compared to control. Surprisingly, the emerged adult flies that developed in medium containing Ag-doped Na2Ti3O7 showed a longer longevity even when compared to animals that developed in standard culture medium or medium containing Na2Ti3O7 NCs. Therefore, our data suggests that Ag-doped Na2Ti3O7 was able to increase the

The toxicity of NCs, such as zinc oxide, titanium dioxide, magnetite, hydroxyapatite, and sodium titanate, is induced through the generation of reactive species and consequent oxidative stress [33–35]. The redox imbalance caused by NCs is capable of generating mitochondrial dysfunctions, inducing inflammatory responses, causing cytotoxicity and genotoxicity, in addition to altering the functioning of the sodium and potassium channels and consequent cell death [33]. Oxidative stress not only causes cell damage and protein oxidation but is also possibly responsible for altering the biosynthesis of hormones, such as ecdysone in insects. Ecdysone is a crucial hormone in the control of metamorphosis and ecdysis events in insects [36, 37]. Our data showed a high larval lethality, especially in animals exposed to Na2Ti3O7, possibly generated by oxidative stress, which can also impair ecdysone biosynthesis, causing developmental problems. One of the forgotten properties of NCs is their antioxidant capacity, such as Ag and cerium oxide

developed in a standard culture medium.

*development, which was partially rescued by the Ag-doped Na2Ti3O7.*

**146**

**Figure 2.**

*(a) Daily pupation analysis of pure and Ag-doped Na2Ti3O7 exposed animals. It is possible to observe that the exposure to pure and Ag-doped Na2Ti3O7 Ag caused no delay in the transition from larva to pupa. (b) Lifespan analysis of pure and Ag-doped Na2Ti3O7 exposed animals. It is shown that Na2Ti3O7 exposure during development decreased adult longevity in about 20 days in comparison to control animals. However, the Ag-doped Na2Ti3O7 not only rescued the animals survival but surprisingly increased it in 10 days in comparison to control animals.*

nanoparticles (CONPs), and some NP of oxide that can even mimic an antioxidant molecule [38].

Therefore, we believe that the reduction in larval lethality observed for Ag-doped Na2Ti3O7 NCs compared to Na2Ti3O7 NCs can be explained by a lesser effect on the generation of reactive species, suggesting that the transition metal silver was sufficient to increase the biocompatibility of Na2Ti3O7 NCs *in vivo*. However, additional studies are crucial to better understand the mechanisms by which development is influenced by nanocrystals.

#### **2.3 Doped nanocrystals embedded in glass systems**

This section will show the results of Zn1-*x*CrxTe NCs, Zn1-*x*CuxTe NCs, and Bi2-x CrxTe3 NCs embedded in glass systems aiming at spintronics applications.

#### *2.3.1 Cr- and Cu-doped ZnTe nanocrystals embedded in glass matrix*

**Figure 4** presents TEM images (**a**) and X-ray diffraction (XRD) (**b**) of samples containing Zn1-*x*CrxTe NCs, with Cr-concentrations ranging from *x* = 0.00 to

#### **Figure 4.**

*TEM images (a) and XRD diffractograms (b) of samples containing Zn1-xCrxTe NCs, with Cr-concentrations ranging from x = 0.00 to x = 0.05; (c) OA spectra of glass samples containing Zn1-xCrxTe NCs, with concentration x = 0.05 and PZABP:0.05Cr; (d) energy diagram of Cr3+ and Cr2+ ions coordinated octahedral (oh) and tetrahedral (td).*

*x* = 0.05. Already the **Figure 4(c)** shows OA spectra of glass samples containing Zn1-*x* CrxTe NCs, with concentration *x* = 0.05 and PZABP glassy matrix doped with 0.05 Cr (PZABP:0.05Cr). In **Figure 4(d)**, energy diagram (below) of Cr3+ and Cr2+ ions coordinated octahedral (Oh) and tetrahedral (Td) of the transitions observed [22].

The formation of Zn1-*x*CrxTe NCs was confirmed by Transmission Electron Microscopy (TEM) images. These images show two distinct groups of spherical NCs attributed to quantum dots (QDs) and bulk NCs, as we reported in our previous work [21]. The average diameters of these NCs are approximately D ~ 4.50 nm for QDs and D ~ 15.31 for bulk NCs. TEM images also show that the distance between their crystallographic planes of these does not vary with the Cr concentration. This suggests invariance in lattice parameter with the incorporation of Cr2+ ions. This result is expected, and is in accordance with what was observed from the XRD difractograms, because the ionic radii of Zn2+ (0.68 nm) and Cr2+ (0.73 nm) are very similar. Thus, XRD show that the position of the peaks, corresponding to (1 1 1), (2 0 0) (2 2 0) and (3 1 1), is the same for all samples. Optical absorption spectra confirm the substitutional incorporation of Cr2+ ions in the ZnTe semiconductor lattice, due the <sup>5</sup> T2( 5 D) → <sup>1</sup> A2( 1 I), 5 T2( 5 D) → <sup>3</sup> A2( 3 F), 5 T2( 5 D) → <sup>3</sup> E(3 H) and 5 T2( 5 D) → <sup>3</sup> T2( 3 H) spin forbidden absorption bands of Cr2+ ions [39], indicated in the energy diagram.

**Figure 5** shows OA spectra and photographs (**a**) of the PZABP template and of Zn1-*x*CuxTe NC samples embedded in this template at different Cu-doping contents: *x* varying from 0.000 to 0.100. **Figure 5**(**b**) shows TEM images for sample with x = 0.05 (**b**) and EPR spectra for sample with x = 0.10 **Figure 5**(**c**) [21]. A redshift in the OA bands assigned to the QDs as Cu concentration increases, shifting from 3.10 eV (400 nm) to 2.95 eV (420 nm), when *x* ranges from 0.00 to 0.10. This decrease in the band gap energy with increase of transition metal (Cu) doped II–IV compound semiconductors can be best understand in terms of *sp–d* spin exchange interaction between band electrons and the localized *d* electrons of the transition metal ions substituting the cations [40]. TEM images confirm the formation of

**149**

unoccupied 3d3

**Figure 5.**

*Doped Semiconductor Nanocrystals: Development and Applications*

Zn1-*x*CuxTe NCs, with interplanar distance around d ~ 0.346 nm. Electron paramagnetic resonance spectra (EPR) confirm the substitutional incorporation, due to

*OA spectra and photographs (a) of the PZABP template and of Zn1-xCuxTe NC samples embedded in this template at different Cu-doping contents: x varying from 0.00 to 0.100. TEM images for sample with x = 0.05* 

The UV–VIS optical absorption (OA) spectra shown in **Figure 6**(**a**) for the host glass matrix SNAB ̶ 45SiO2·30Na2CO3·5Al2O3·20B2O3 (mol%) of the Bi2-xCrxTe3 NCs with xCr molar fraction (x = 0.00; 0.01; 0.05) provides strong evidence of the formation and incorporation of Cr3+ ions in orthorhombic sites of Bi2Te3 NCs. The SNAB matrix with a band gap of approximately 4 eV [26], is an ideal template for observing d-d and excitonic transitions in Bi2-xCrxTe3 NCs as shown by the spec-

Bi2Te3 is a V - VI semiconductor that presents a narrow band gap of 0.13 eV in bulk form at room temperature [41]. The tail of the band attributed to the absorption of the charge carriers (electron–hole pair) shows the result of the nucleation and formation of the Bi2Te3 NCs with a confinement energy around 3.10 eV. The slight blueshift observed for the Bi2-xCrxTe3 NCs (x = 0.01; 0.05) is due to the strong sp-d exchange interactions between Bi2Te3 (sp) excitons and the electrons of the

properties of the intrinsic semiconductor, proportional to the increase in Cr content. Finally, the sharpness of the bands of increasing intensity observed in the visible spectral region is due to the 3d-3d electronic transitions of the Cr ions [26, 42].

orbitals of the Cr3+ ion. This orbital coupling modifies the optical

configuration.

hyperfine transitions characteristic Cu2+ ions with d9

*(b) and EPR spectra for sample with x = 0.10 (c).*

*2.3.2 Cr-doped Bi2Te3 nanocrystals embedded in glass systems*

trum's bottom line (black) with no band in the visible region.

*DOI: http://dx.doi.org/10.5772/intechopen.96753*

*Doped Semiconductor Nanocrystals: Development and Applications DOI: http://dx.doi.org/10.5772/intechopen.96753*

#### **Figure 5.**

*Materials at the Nanoscale*

*x* = 0.05. Already the **Figure 4(c)** shows OA spectra of glass samples containing Zn1-*x* CrxTe NCs, with concentration *x* = 0.05 and PZABP glassy matrix doped with 0.05 Cr (PZABP:0.05Cr). In **Figure 4(d)**, energy diagram (below) of Cr3+ and Cr2+ ions coordinated octahedral (Oh) and tetrahedral (Td) of the transitions observed [22]. The formation of Zn1-*x*CrxTe NCs was confirmed by Transmission Electron Microscopy (TEM) images. These images show two distinct groups of spherical NCs attributed to quantum dots (QDs) and bulk NCs, as we reported in our previous work [21]. The average diameters of these NCs are approximately D ~ 4.50 nm for QDs and D ~ 15.31 for bulk NCs. TEM images also show that the distance between their crystallographic planes of these does not vary with the Cr concentration. This suggests invariance in lattice parameter with the incorporation of Cr2+ ions. This result is expected, and is in accordance with what was observed from the XRD difractograms, because the ionic radii of Zn2+ (0.68 nm) and Cr2+ (0.73 nm) are very similar. Thus, XRD show that the position of the peaks, corresponding to (1 1 1), (2 0 0) (2 2 0) and (3 1 1), is the same for all samples. Optical absorption spectra confirm the substitutional incorporation of Cr2+ ions in the ZnTe semicon-

*TEM images (a) and XRD diffractograms (b) of samples containing Zn1-xCrxTe NCs, with Cr-concentrations* 

*ranging from x = 0.00 to x = 0.05; (c) OA spectra of glass samples containing Zn1-xCrxTe NCs, with concentration x = 0.05 and PZABP:0.05Cr; (d) energy diagram of Cr3+ and Cr2+ ions coordinated octahedral* 

**148**

5 T2( 5 D) → <sup>3</sup>

**Figure 4.**

*(oh) and tetrahedral (td).*

ductor lattice, due the <sup>5</sup>

the energy diagram.

T2( 3 T2( 5 D) → <sup>1</sup>

A2( 1 I), 5 T2( 5 D) → <sup>3</sup>

A2( 3 F), 5 T2( 5 D) → <sup>3</sup>

H) spin forbidden absorption bands of Cr2+ ions [39], indicated in

**Figure 5** shows OA spectra and photographs (**a**) of the PZABP template and of Zn1-*x*CuxTe NC samples embedded in this template at different Cu-doping contents: *x* varying from 0.000 to 0.100. **Figure 5**(**b**) shows TEM images for sample with x = 0.05 (**b**) and EPR spectra for sample with x = 0.10 **Figure 5**(**c**) [21]. A redshift in the OA bands assigned to the QDs as Cu concentration increases, shifting from 3.10 eV (400 nm) to 2.95 eV (420 nm), when *x* ranges from 0.00 to 0.10. This decrease in the band gap energy with increase of transition metal (Cu) doped II–IV compound semiconductors can be best understand in terms of *sp–d* spin exchange interaction between band electrons and the localized *d* electrons of the transition metal ions substituting the cations [40]. TEM images confirm the formation of

E(3

H) and

*OA spectra and photographs (a) of the PZABP template and of Zn1-xCuxTe NC samples embedded in this template at different Cu-doping contents: x varying from 0.00 to 0.100. TEM images for sample with x = 0.05 (b) and EPR spectra for sample with x = 0.10 (c).*

Zn1-*x*CuxTe NCs, with interplanar distance around d ~ 0.346 nm. Electron paramagnetic resonance spectra (EPR) confirm the substitutional incorporation, due to hyperfine transitions characteristic Cu2+ ions with d9 configuration.

#### *2.3.2 Cr-doped Bi2Te3 nanocrystals embedded in glass systems*

The UV–VIS optical absorption (OA) spectra shown in **Figure 6**(**a**) for the host glass matrix SNAB ̶ 45SiO2·30Na2CO3·5Al2O3·20B2O3 (mol%) of the Bi2-xCrxTe3 NCs with xCr molar fraction (x = 0.00; 0.01; 0.05) provides strong evidence of the formation and incorporation of Cr3+ ions in orthorhombic sites of Bi2Te3 NCs. The SNAB matrix with a band gap of approximately 4 eV [26], is an ideal template for observing d-d and excitonic transitions in Bi2-xCrxTe3 NCs as shown by the spectrum's bottom line (black) with no band in the visible region.

Bi2Te3 is a V - VI semiconductor that presents a narrow band gap of 0.13 eV in bulk form at room temperature [41]. The tail of the band attributed to the absorption of the charge carriers (electron–hole pair) shows the result of the nucleation and formation of the Bi2Te3 NCs with a confinement energy around 3.10 eV. The slight blueshift observed for the Bi2-xCrxTe3 NCs (x = 0.01; 0.05) is due to the strong sp-d exchange interactions between Bi2Te3 (sp) excitons and the electrons of the unoccupied 3d3 orbitals of the Cr3+ ion. This orbital coupling modifies the optical properties of the intrinsic semiconductor, proportional to the increase in Cr content. Finally, the sharpness of the bands of increasing intensity observed in the visible spectral region is due to the 3d-3d electronic transitions of the Cr ions [26, 42].

#### **Figure 6.**

*(a) Optical absorption spectra at room temperature of Bi2-xCrxTe3 NCs (x = 0.00; 0.01; 0.05) embedded in SNAB glass matrix. For comparison purposes, the absorption spectrum of the SNAB glass matrix represents on the black bottom line. The inset shows the Tanabe-Sugano diagram d3 of octahedral symmetry (C/B = 4.5) for the [CrTe6] 9− complex and the respective spin allowed and forbidden transitions indicated on the energy 10 Dq = 2.16 eV. (b) TEM image of Bi2-xCrxTe3 NCs (x = 0.05) embedded in SNAB glass. (c) Details of the quintuple layer and the van der Waals gap in the Bi2T3 hexagonal unit cell with the substitutional doping of Bi3+ ions by Cr3+ in distorted octahedral sites. (d) EPR spectra in the X band, at 300 K for NCs of Bi2-xCrxTe3 NCs (x = 0.00; 0.01; 0.05) embedded in the SNAB glass matrix. The inset shows the split diagram of the energy states of the system.*

The energy states identified in the OA spectrum of figure x (a) belong to the spin allowed and forbidden d-d transitions: 4 A2( 4 F) → <sup>2</sup> Eg (2 G) (1.83 eV), 4 A2( 4 F) → <sup>2</sup> T1( 2 G) (1.91 eV), <sup>4</sup> A2g (4 F) → <sup>4</sup> T2g (4 F) (2.16 eV), <sup>4</sup> A2g (4 F) → <sup>2</sup> T2g (2 G) (2.76 eV) and 4 A2 (4 F) → <sup>4</sup> T1 (4 F) (3.06 eV). These transitions are in accordance with a Tanabe-Sugano diagram d3 of octahedral symmetry for C/B = 4.5 (see inset in **Figure 6a**) [43]. The results are typical of inter-electronic repulsion parameters (Racah) B = 0.088 eV in a crystal field strength 10 Dq (∆) = 2.16 eV of Cr3+ ions in coordinated octahedral sites of Te ([CrTe6] 9−) ligands [42, 44].

The exciton Bohr radius of approximately 50 nm for Bi2Te3 bulk [45] makes the semiconductor subject to strong quantum confinements. **Figure 6**(**b**) shows the TEM image of the SNAB glass matrix host of the Bi2-xCrxTe3 NCs (x = 0.05). The nanocrystal's 5 nm size confirms the formation of Bi2-xCrxTe3 quantum dots due to the strong quantum confinement of the semiconductor structure.

The quantum size of the Bi2-xCrxTe3 NCs does not change with the increase of Cr incorporation in the samples. In this way, the structure preserves due to the nonsaturation of the molar fraction of Cr doping in the Bi2-xCrxTe3 NCs. The interplanar distance d015 = 0.321 nm is evidence of Tellurobismuthite's hexagonal crystalline structure [27, 41]. **Figure 6**(**c**) shows the hexagonal unit cell *Rm D*− *<sup>d</sup>* <sup>5</sup> 3 <sup>3</sup> [41] of the

Cr-doped Bi2Te3 NCs with the atomic arrangement of monoatomic planes Te - Cr - Te - Bi - Te and Te - Bi - Te - Bi - Te in terms of quintuple layers linked by weak van der Waals interactions [41]. The substitutional doping of Cr3+ ions with a smaller ionic radius (0.53 Å) in relation to Bi3+ (1.03 Å) distorts the environment of octahedral symmetry [42].

**151**

*Doped Semiconductor Nanocrystals: Development and Applications*

development of spintronic nanodevices [24, 25, 27, 28].

**Figure 6**(**d**) shows the EPR measurements in the X band, at 300 K for the Bi2-xCrxTe3 NCs (x = 0.00; 0.01; 0.05) samples embedded in the SNAB glass matrix. The EPR spectrum for Bi2Te3 not doped does not show any signal due to the absence of doping ions. However, the central signal characteristic of a Ms. = ± ½ transition typical of a fine structure line results from the interaction between the electronic (S = 3/2) and nuclear (I = 0) spins of Cr3+ ions in an octahedral crystal field. The inset in **Figure 6(d)** shows the split diagram of the energy states involved in the system. The increasing molar fraction of Cr ions in the Bi2-xCrxTe3 results in greater dipole–dipole interaction and, consequently, an increase in the observed RPE

Therefore, the long-range magnetic properties generated by the domain of the Cr ion doping spins, in addition to the insulating topological states of the Bi2Te3 semiconductor NCs, have aroused great interest in the scientific community for the

Therefore, this chapter showed the development and applications of several doped semiconductor nanocrystals, as nanopowders or embedded in glass systems. Doped Nanocrystals show good potential to control plant diseases as controlling bacterial diseases on field crops is complex. We also demonstrate that depending on the ion incorporated in the nanocrystal structure, the biocompatibility could be improved. Additionally, we show magnetic properties generated by the domain of the Cu or Cr ions doping spins, in addition to semiconductor nanocrystals embed-

ded in glass systems, for the development of spintronic nanodevices.

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

*DOI: http://dx.doi.org/10.5772/intechopen.96753*

signal's intensity [26].

**3. Conclusion**

**Acknowledgements**

**Conflict of interest**

The authors declare no conflict of interest.

*Doped Semiconductor Nanocrystals: Development and Applications DOI: http://dx.doi.org/10.5772/intechopen.96753*

**Figure 6**(**d**) shows the EPR measurements in the X band, at 300 K for the Bi2-xCrxTe3 NCs (x = 0.00; 0.01; 0.05) samples embedded in the SNAB glass matrix. The EPR spectrum for Bi2Te3 not doped does not show any signal due to the absence of doping ions. However, the central signal characteristic of a Ms. = ± ½ transition typical of a fine structure line results from the interaction between the electronic (S = 3/2) and nuclear (I = 0) spins of Cr3+ ions in an octahedral crystal field. The inset in **Figure 6(d)** shows the split diagram of the energy states involved in the system. The increasing molar fraction of Cr ions in the Bi2-xCrxTe3 results in greater dipole–dipole interaction and, consequently, an increase in the observed RPE signal's intensity [26].

Therefore, the long-range magnetic properties generated by the domain of the Cr ion doping spins, in addition to the insulating topological states of the Bi2Te3 semiconductor NCs, have aroused great interest in the scientific community for the development of spintronic nanodevices [24, 25, 27, 28].
