**2. Development of technology for growth of GaP nanocrystals**

While bulk and thin film GaP has been successfully commercialized for many years, its ap‐ plication in nanocomposites as a new optical medium has only received attention recently. This section reviews our recent efforts to advance the quality of GaP nanoparticles for light emissive devices based on polymer/GaP nanocomposites.

This activity is the important milestone in the creation of the nanocomposites for advanced light emissive device structures because GaP nanoparticles having the necessary lumines‐ cent and electroluminescent properties and compatible with a polymer matrix is a key ele‐ ment of these structures. We hope the described here some details and parameters of the technological processes used for fabrication of GaP nanocrystals with the improved and nec‐ essary for concrete application characteristics of luminescence will be useful in further elab‐ oration of the relevant optoelectronic devices.

The quality of GaP nanoparticles was improved using mild aqueous synthesis and different colloidal reactions of Ga and P sources in toluene [26-38]. We used these methods taking in‐ to account that success of our activity depends on optimal choice of the types of chemical reactions, necessary chemicals and their purity, conditions of the synthesis (control accura‐ cy, temperature, pressure, duration, etc.), methods and quality of purification of the nano‐ crystals, storage conditions for nanoparticles used in the further operations of fabrication of the GaP/nanocomposites.

Ultrasonication and ultracentrifugation have been applied during the synthesis and selec‐ tion of nanoparticles to increase their quality and to select them on dimensions.

The relevant spectra of photoluminescence and Raman light scattering, X-ray diffraction and electron microscopy of the nanoparticles prepared under different conditions have been compared with each other as well as with those from bulk single crystals. Thoroughly-pre‐ pared powders and suspensions of the nanoparticles have been used for preparation of GaP film nanocomposites on the base of different polymers compatible with the nanoparticles on optical and mechanical properties.

#### **2.1. Equipment for fabrication of nanoparticles, fluoropolymers and nanocomposites**

The equipment for fabrication of fluoropolymers and polymer nanocomposites has been ela‐ borated by the author (JB) from Clemson University during our joint activity on light emis‐ sive structures. This equipment and approaches were applied to our specific needs without any serious modification.

#### *2.1.1. Equipment for sublimation of phosphorus*

thermoplastics with suitable for GaP nanoparticles optical, electrical, thermal, and envi‐

Perfect single crystals from our unique collection of pure and doped GaP single crystals [1-25] compared with GaP nanoparticles prepared by us [26-31] serve as a standard yielding funda‐ mental new knowledge and insights into semiconductor optical physics. Elaborating optimal methods of fabrication of GaP nanoparticles and their light emissive composites with compati‐ ble polymers [32-36] we use our own experience and literature data [37-39]. Due to considera‐ ble efforts in the past, including our contribution also, GaP has received significant attention as a material for use in a wide range of important modern optoelectronic devices including pho‐ todetectors, light emitters, electroluminescent displays and power diodes as well as being a model material with which to investigate the fundamental properties of semiconductors.

These two components of the composites, GaP and specially selected polymers, were unified based on their compatibility with the light emission spectral region as well as in their eventual integration into all optical circuits where bulk crystals or nanocrystals of GaP have been of commercial interest mainly for fiber and planar light emissive and micro-optic elements.

We hope our device structures obtained with application of accumulated for years results in their optics and technology [1-36, 41-43] will have significant commercial value because they

While bulk and thin film GaP has been successfully commercialized for many years, its ap‐ plication in nanocomposites as a new optical medium has only received attention recently. This section reviews our recent efforts to advance the quality of GaP nanoparticles for light

This activity is the important milestone in the creation of the nanocomposites for advanced light emissive device structures because GaP nanoparticles having the necessary lumines‐ cent and electroluminescent properties and compatible with a polymer matrix is a key ele‐ ment of these structures. We hope the described here some details and parameters of the technological processes used for fabrication of GaP nanocrystals with the improved and nec‐ essary for concrete application characteristics of luminescence will be useful in further elab‐

The quality of GaP nanoparticles was improved using mild aqueous synthesis and different colloidal reactions of Ga and P sources in toluene [26-38]. We used these methods taking in‐ to account that success of our activity depends on optimal choice of the types of chemical reactions, necessary chemicals and their purity, conditions of the synthesis (control accura‐ cy, temperature, pressure, duration, etc.), methods and quality of purification of the nano‐ crystals, storage conditions for nanoparticles used in the further operations of fabrication of

**2. Development of technology for growth of GaP nanocrystals**

ronment resistant properties.

2 Optoelectronics - Advanced Materials and Devices

present a new optical medium and product.

emissive devices based on polymer/GaP nanocomposites.

oration of the relevant optoelectronic devices.

the GaP/nanocomposites.

It was found the synthesis on the base of white phosphorus gives the best quality of GaP nano‐ particles. Due to the known prohibition for free sale of white phosphorus we have elaborated the facilities for its preparation using sublimation of its red modification (see Figure 1).

**Figure 1.** Preparation of white phosphorus.

The device is the silica tube, which is hermetic to the air, and is heated from one end while the P vapor is transferred by a neutral gas (nitrogen or argon) environment at the other cooled end of the tube where it is condensed there to form white phosphorus. After comple‐ tion of the process the white phosphorus can be removed; the tube must be immersed into a water bath that to avoid inflammation of phosphorus in air.

The obtained white phosphorus must be stored as a water suspension. Then this suspen‐ sion by melting in boiled water is turned into the substance using in the synthesis of GaP nanoparticles.

#### *2.1.2. Equipment for hydrothermal and colloidal synthesis*

A new model of autoclave for the hydrothermal synthesis of GaP nanoparticles from the ap‐ propriate chemical solutions has been established given the requisite high temperatures (up to 500°C) for the organic solvents using GaCl3•6H2O and white phosphorus as precursors. Software for the process of synthesis at the temperature control and regulation with the ac‐ curacy of 0.1°C has been developed.

ly inhibiting their further growth. Therefore, we have elaborated the methods of GaP nano‐ crystals colloidal synthesis using NaBH4 and Na3P compounds (Subsections 2.2.2 and 2.2.3).

Noted here are only essential details of the aqueous syntheses of GaP nanoparticles pre‐

Using the literature data noted above the first nanocrystalline samples of GaP [26] have been prepared. The first aqueous prepared, relatively monodisperse, well crystallized GaP nano‐ crystallites, exhibiting pronounced quantum confinement effect have been presented in [27]. The relevant reactions were carried out in an aqueous solution at 120-160°C. A typical syn‐ thesis was as follows: 35,0 ml H2O, 1,0 g Ga2O3, 1,0 g NaOH, 2,0 g white phosphorus were added to a 50 ml Teflon –lined autoclave, and 1,5 g I2 then was added. The autoclave was

GaP nanoparticles were obtained in an alkali solution, taking advantage of the reaction of Ga(OH)4 with PH3 which was produced from white phosphorus dispersed in alkali solution:


4 2 3 22

P 3OH 3H O PH 3H PO Ga O 2OH 3H O 2Ga OH

+ + ®+ ++®

2 3 2 4 43 2

Ga(OH PH GaP 3H O OH

P 2I 4OH 4H O 2PH 2H PO 4I 4 2 2 3 34


The yield of GaP in alkali solution is only about 12%. In order to improve the yield of GaP iodine was added to induce the reaction with white phosphorus, based on follow process:

The X-ray powder diffraction patterns of the as-prepared products indicated to the zinc blend structure of GaP with a= 5.43 Å. Average crystallite size estimated by the Scherrer

Nanoparticles of GaP have been prepared by mild aqueous synthesis at different tempera‐

NaOH pellets were dissolved in distilled water. Ga2O3, red or white phosphorus powder and I2 were mixed and added to the NaOH solution. The mixed solution was then placed into an autoclave and heated in an oven for 8 hours at 125 or 200°C. After the completion of heating the autoclave was taken out of the oven and cooled. The obtained powder was fil‐ tered, washed with ethanol, HCl and distilled water and dried or ultrasonicated in the bath with a special solvent for separation in dimensions and preparation of a suspension for any nanocomposite. The dried powders were then characterized using standard methods of XRD, TEM, Raman scattering and photoluminescence. For comparison industrial and spe‐

( )




Advanced Light Emissive Device Structures http://dx.doi.org/10.5772/52416

(1)

5

*2.2.1. Hydrothermal method of synthesis of GaP nanocrystals*

pared at different temperatures and reaction conditions.

kept at 120-160°C for 8 hrs and then cooled to room temperature.

equation are about 5 nm for GaP nanocrystals [27].

tures, modifications and compositions of the reacting components.

cially grown and aged GaP single crystals also were used [1, 24].

The key part of the method are the chemical reactions at high temperature and pressure. The reactor here is a hollow hermetic teflon cylinder. The necessary temperature (125°С, 200°С) inside the cylinder is obtained by its heating, while the pressure – by evaporation of water.

**Figure 2.** Equipment for preparation of GaP nanocrystals on the base of NaBH4 or Na3P.

The equipment for colloidal synthesis of GaP nanocrystals using NaBH4 or Na3P in toluene is shown in Figure 2.

#### **2.2. Elaboration of technologies for fabrication of GaP nanoparticles**

In 2005 the authors developed methods to fabricate GaP nanoparticles [26]. So, the technolo‐ gy and properties of the nanoparticles obtained in 2005-2006 and later [27, 28] are a good reference point for comparison to the new data provided herein.

More recently the authors [31] have concentrated on low temperature methods to synthesize GaP nanoparticles with improved luminescent characteristics. These methods are considera‐ bly different from those of other standard high temperature methods.

The first samples of GaP nanoparticles having a distinct luminescence at room temperature were obtained by hydrothermal method from aqueous solutions at relative low temperature (120-200°C). This method is discussed in Subsection 2.2.1. It was found that the composition of the nanoparticles corresponds to stoichiometric GaP.

The colloidal method provides a good opportunity to control the conditions of the synthesis, to decrease power inputs and to increase quality of nanoparticles concerning their purity and uniformity of their dimensions. In actuality, the single parameter, which may be con‐ trolled in the other methods, is the temperature, while using colloidal methods one can con‐ trol nucleation of nanoparticles as well as velocity of their growth. The other important advantage of the colloidal method is the ability of so called "capping"; that is to isolate nanoparticles from each other, to prevent their agglomeration during storage, simultaneous‐ ly inhibiting their further growth. Therefore, we have elaborated the methods of GaP nano‐ crystals colloidal synthesis using NaBH4 and Na3P compounds (Subsections 2.2.2 and 2.2.3).

#### *2.2.1. Hydrothermal method of synthesis of GaP nanocrystals*

to 500°C) for the organic solvents using GaCl3•6H2O and white phosphorus as precursors. Software for the process of synthesis at the temperature control and regulation with the ac‐

The key part of the method are the chemical reactions at high temperature and pressure. The reactor here is a hollow hermetic teflon cylinder. The necessary temperature (125°С, 200°С) inside the cylinder is obtained by its heating, while the pressure – by evaporation of water.

The equipment for colloidal synthesis of GaP nanocrystals using NaBH4 or Na3P in toluene

In 2005 the authors developed methods to fabricate GaP nanoparticles [26]. So, the technolo‐ gy and properties of the nanoparticles obtained in 2005-2006 and later [27, 28] are a good

More recently the authors [31] have concentrated on low temperature methods to synthesize GaP nanoparticles with improved luminescent characteristics. These methods are considera‐

The first samples of GaP nanoparticles having a distinct luminescence at room temperature were obtained by hydrothermal method from aqueous solutions at relative low temperature (120-200°C). This method is discussed in Subsection 2.2.1. It was found that the composition

The colloidal method provides a good opportunity to control the conditions of the synthesis, to decrease power inputs and to increase quality of nanoparticles concerning their purity and uniformity of their dimensions. In actuality, the single parameter, which may be con‐ trolled in the other methods, is the temperature, while using colloidal methods one can con‐ trol nucleation of nanoparticles as well as velocity of their growth. The other important advantage of the colloidal method is the ability of so called "capping"; that is to isolate nanoparticles from each other, to prevent their agglomeration during storage, simultaneous‐

**Figure 2.** Equipment for preparation of GaP nanocrystals on the base of NaBH4 or Na3P.

**2.2. Elaboration of technologies for fabrication of GaP nanoparticles**

bly different from those of other standard high temperature methods.

reference point for comparison to the new data provided herein.

of the nanoparticles corresponds to stoichiometric GaP.

curacy of 0.1°C has been developed.

4 Optoelectronics - Advanced Materials and Devices

is shown in Figure 2.

Noted here are only essential details of the aqueous syntheses of GaP nanoparticles pre‐ pared at different temperatures and reaction conditions.

Using the literature data noted above the first nanocrystalline samples of GaP [26] have been prepared. The first aqueous prepared, relatively monodisperse, well crystallized GaP nano‐ crystallites, exhibiting pronounced quantum confinement effect have been presented in [27]. The relevant reactions were carried out in an aqueous solution at 120-160°C. A typical syn‐ thesis was as follows: 35,0 ml H2O, 1,0 g Ga2O3, 1,0 g NaOH, 2,0 g white phosphorus were added to a 50 ml Teflon –lined autoclave, and 1,5 g I2 then was added. The autoclave was kept at 120-160°C for 8 hrs and then cooled to room temperature.

GaP nanoparticles were obtained in an alkali solution, taking advantage of the reaction of Ga(OH)4 with PH3 which was produced from white phosphorus dispersed in alkali solution:

$$\text{P}\_4 + 3\text{OH}^- + 3\text{H}\_2\text{O} \rightarrow \text{PH}\_3 + 3\text{H}\_2\text{PO}\_2^-$$

$$\text{Ga}\_2\text{O}\_3 + 2\text{OH}^- + 3\text{H}\_2\text{O} \rightarrow 2\text{Ga} \text{(OH)}\_4^- \tag{1}$$

$$\text{Ga} (\text{OH}\_4-\text{ }+\text{PH}\_3 \rightarrow \text{GaP} + 3\text{H}\_2\text{O} + \text{OH}^-$$

The yield of GaP in alkali solution is only about 12%. In order to improve the yield of GaP iodine was added to induce the reaction with white phosphorus, based on follow process:

$$\rm P\_4 + \, 2I\_2 + 4OH^- + 4H\_2O \to 2PH\_3 + 2H\_3PO\_4 + 4I \tag{2}$$

The X-ray powder diffraction patterns of the as-prepared products indicated to the zinc blend structure of GaP with a= 5.43 Å. Average crystallite size estimated by the Scherrer equation are about 5 nm for GaP nanocrystals [27].

Nanoparticles of GaP have been prepared by mild aqueous synthesis at different tempera‐ tures, modifications and compositions of the reacting components.

NaOH pellets were dissolved in distilled water. Ga2O3, red or white phosphorus powder and I2 were mixed and added to the NaOH solution. The mixed solution was then placed into an autoclave and heated in an oven for 8 hours at 125 or 200°C. After the completion of heating the autoclave was taken out of the oven and cooled. The obtained powder was fil‐ tered, washed with ethanol, HCl and distilled water and dried or ultrasonicated in the bath with a special solvent for separation in dimensions and preparation of a suspension for any nanocomposite. The dried powders were then characterized using standard methods of XRD, TEM, Raman scattering and photoluminescence. For comparison industrial and spe‐ cially grown and aged GaP single crystals also were used [1, 24].

Figure 4 shows the Raman light scattering spectra from GaP nanoparticles prepared us‐ ing white or red P in mild aqueous synthesis at increased or low temperatures and ul‐

In the colloidal method of the synthesis freshly prepared white phosphorus was used and ultrasonicated in toluene. Here the mixture for the reaction of the synthesis consists of

The characteristic GaP Raman lines from aged GaP single crystals (Figure 4, spectrum 1) and from the nanoparticles prepared using white P at low temperature (Figure 4, spectrum 4) were narrow and intense whereas, nanoparticles prepared from red P at higher tempera‐ tures (Figure 4, spectra 2 and 3) were weak and broad; the especially weak and broad spec‐

**Figure 5.** X-ray diffraction from GaP nanoparticles.1. White phosphorus, using low temperature syntheses, well-treat‐ ed powder. 2. White P, not the best performance and powder treatment. 3. Red phosphorus, the best result. 4. Perfect

In Figure 5 one can see x-ray diffraction from the GaP nanoparticles prepared at different conditions using red or white phosphorus (spectra 1-3) in comparison with the diffraction from perfect GaP single crystal (spectrum 4). The nanoparticles obtained by low tempera‐ ture aqueous synthesis using white phosphorus exhibited clear and narrow characteristic lines like those obtained from perfect GaP bulk single crystals taken from our unique collec‐ tion of long-term (app. 50 years) ordered GaP single crystals (Figure 5, spectra 1 and 4). Con‐ trary to that, nanoparticles prepared using red phosphorus or less-than-optimum conditions

Any luminescence was absent in newly-made industrial and our freshly prepared crystals but it was bright in the same app. 50 years aged crystals (Figure 6, spectrum 1; the features of luminescence in the perfect aged crystals please see in [16-25]). Initial results on lumines‐ cent properties of GaP nanoparticles [26] confirmed the preparation of GaP nanoparticles

showed broad and weak characteristic lines (Figure 5, spectra 2 and 3).

containing the nanoparticles, was treated in an high-speed ultracentrifuge.

trum exhibits not thoroughly washed powder (please see spectrum 2).

 nH2O diluted in toluene and dry NaBH4. One of 2 fractions of different colors ob‐ tained in the synthesis was removed by rinsing in ethanol and water while the next one,

Advanced Light Emissive Device Structures http://dx.doi.org/10.5772/52416 7

trasonically treated.

GaCl3 .

GaP bulk crystal.

**Figure 3.** TEM images of GaP nanoparticles obtained by the aqueous synthesis. a. Thoroughly ultrasonicated and dried nanopowder. b. Initial clusters with the dimensions of the order of 100 nm.

The instruments employed for Raman light scattering and luminescence measurements in‐ cluded spectrographs interfaced to a liquid nitrogen-cooled detector and an argon ion laser or lamp excitation sources. Raman scattering spectra was obtained at room temperature by exci‐ tation with 514.5 nm radiation. Luminescence was excited by UV light of the lamps or the N2 la‐ ser nanosecond pulses at wavelength 337 nm and measured at room temperature [25-28].

Figure 3 shows the TEM images of GaP nanoparticles obtained by the aqueous synthesis. The washed, thoroughly ultrasonicated and dried nanopowder contains mainly single 10nm nanoparticles (Figure 3a), obtained from the initial clusters with the dimensions of the order of 100 nm (Figure 3b).

**Figure 4.** Raman light scattering from GaP nanoparticles of different treatment (spectra 2-4) in comparison with per‐ fect GaP bulk crystals (spectrum 1).

Spectrum 2: Not thoroughly treated powder of nanoparticles prepared using red phospho‐ rus at 200°C. Spectrum 3: Thoroughly treated GaP nanoparticles prepared using red phos‐ phorus at 200°C. Spectrum 4: Nanoparticles prepared on the base of white P by low temperature syntheses.

Figure 4 shows the Raman light scattering spectra from GaP nanoparticles prepared us‐ ing white or red P in mild aqueous synthesis at increased or low temperatures and ul‐ trasonically treated.

In the colloidal method of the synthesis freshly prepared white phosphorus was used and ultrasonicated in toluene. Here the mixture for the reaction of the synthesis consists of GaCl3 . nH2O diluted in toluene and dry NaBH4. One of 2 fractions of different colors ob‐ tained in the synthesis was removed by rinsing in ethanol and water while the next one, containing the nanoparticles, was treated in an high-speed ultracentrifuge.

The characteristic GaP Raman lines from aged GaP single crystals (Figure 4, spectrum 1) and from the nanoparticles prepared using white P at low temperature (Figure 4, spectrum 4) were narrow and intense whereas, nanoparticles prepared from red P at higher tempera‐ tures (Figure 4, spectra 2 and 3) were weak and broad; the especially weak and broad spec‐ trum exhibits not thoroughly washed powder (please see spectrum 2).

**Figure 3.** TEM images of GaP nanoparticles obtained by the aqueous synthesis. a. Thoroughly ultrasonicated and

The instruments employed for Raman light scattering and luminescence measurements in‐ cluded spectrographs interfaced to a liquid nitrogen-cooled detector and an argon ion laser or lamp excitation sources. Raman scattering spectra was obtained at room temperature by exci‐ tation with 514.5 nm radiation. Luminescence was excited by UV light of the lamps or the N2 la‐ ser nanosecond pulses at wavelength 337 nm and measured at room temperature [25-28].

Figure 3 shows the TEM images of GaP nanoparticles obtained by the aqueous synthesis. The washed, thoroughly ultrasonicated and dried nanopowder contains mainly single 10nm nanoparticles (Figure 3a), obtained from the initial clusters with the dimensions of the order

**Figure 4.** Raman light scattering from GaP nanoparticles of different treatment (spectra 2-4) in comparison with per‐

Spectrum 2: Not thoroughly treated powder of nanoparticles prepared using red phospho‐ rus at 200°C. Spectrum 3: Thoroughly treated GaP nanoparticles prepared using red phos‐ phorus at 200°C. Spectrum 4: Nanoparticles prepared on the base of white P by low

dried nanopowder. b. Initial clusters with the dimensions of the order of 100 nm.

of 100 nm (Figure 3b).

6 Optoelectronics - Advanced Materials and Devices

fect GaP bulk crystals (spectrum 1).

temperature syntheses.

**Figure 5.** X-ray diffraction from GaP nanoparticles.1. White phosphorus, using low temperature syntheses, well-treat‐ ed powder. 2. White P, not the best performance and powder treatment. 3. Red phosphorus, the best result. 4. Perfect GaP bulk crystal.

In Figure 5 one can see x-ray diffraction from the GaP nanoparticles prepared at different conditions using red or white phosphorus (spectra 1-3) in comparison with the diffraction from perfect GaP single crystal (spectrum 4). The nanoparticles obtained by low tempera‐ ture aqueous synthesis using white phosphorus exhibited clear and narrow characteristic lines like those obtained from perfect GaP bulk single crystals taken from our unique collec‐ tion of long-term (app. 50 years) ordered GaP single crystals (Figure 5, spectra 1 and 4). Con‐ trary to that, nanoparticles prepared using red phosphorus or less-than-optimum conditions showed broad and weak characteristic lines (Figure 5, spectra 2 and 3).

Any luminescence was absent in newly-made industrial and our freshly prepared crystals but it was bright in the same app. 50 years aged crystals (Figure 6, spectrum 1; the features of luminescence in the perfect aged crystals please see in [16-25]). Initial results on lumines‐ cent properties of GaP nanoparticles [26] confirmed the preparation of GaP nanoparticles with dimensions of between 10-100 nm and clear quantum confinement effects but the lumi‐ nescent spectrum was not bright enough and its maximum was only slightly shifted to UV side against the 2.24 eV forbidden gap at room temperature (Figure 6, spectrum 2). The nanoparticles obtained from the reaction with white P at low (125°C) temperature exhibit bright broad band spectra considerably shifted to UV side [27, 28, 36] (Figure 6, spectrum 3, 4). Note that the original powder contains only a part of GaP particles with nearly 10 nm dimension, which develop quantum confinement effect and the relevant spectrum of lumi‐ nescence, so the spectrum of luminescence consists of this band with maximum at 3 eV and of the band characterizing big particles with the maximum close to the edge of the forbidden gap in GaP (Figure 6, spectrum 3), but thorough ultrasonic treatment gives an opportunity to get the pure fraction of nanoparticles with the spectrum 4 having the maximum at 3 eV.

device structures. More detailed analyses and discussion of these results can be found in the

In the method employed here, NaBH4 was used as a deoxidizer during the synthesis in the solvent – toluene, where the sources of Ga and P (white phosphorus) have been dissolved (GaCl3) or suspended. NaBH4 can be used also due to its high solubility in ethanol. The etha‐ nol solution of NaBH4 was introduced into the process of the synthesis during 5 hours, con‐

White-yellow precipitates were the result of the synthesis. The precipitate was rinsed multi‐ ple times in toluene, removing the remaining P and GaCl3, and then in water, removing the water- soluble species such as NaCl. The centrifugal separation from the solvent has been

3 4 26 2

(3)

9

Advanced Light Emissive Device Structures http://dx.doi.org/10.5772/52416

+ -® + + + ® + +® + + +

3 4 26 2

The last reaction is the closing one, including creation of NaCl, which can be easily removed with deionized water. The main problem of the described synthesis is the exclusion Ga met‐ al particles in the precipitate. The problem is controled via the rate of Ga ion deoxidation, depending on temperature, the types of solvent and deoxidizer. Using low (~1 mL/min) rate of introduction of NaBH4 ethanol solution into the process helps to avoid the metal Ga crea‐

For the preparation of Na3P we used elementary Na, white P and the mixture of InCl3/ GaCl3 (4 wt% InCl3 + 96 wt% GaCl3). The main experimental procedures can be described as follows: a 5.2 g mixture of GaCl3 and InCl3 was dissolved in 150 ml of xylene. Then, 2 g of sodium and 0.9 g of white phosphorus were added into the solution. The solution was stirred at 100°C for 10 hrs. After the reaction, the product was filtered for 3 times in xy‐ lene and 3 times in deionized water. The resultant powders were dried in vacuum at 60– 80°C for 2 hrs. All the above mentioned manipulations were conducted in high purity ni‐ trogen (99.999%) atmosphere in a glove box. Lastly, three equal parts of the product was heated respectively to 300°C, 480°C and 600°C for 1 hr in pure nitrogen (99.999%) flows.

4GaCl 12NaBH 4P 4GaP 12NaCl 6B H 6H

references cited above and will be futher published.

*2.2.2. Synthesis of GaP nanocrystals on the base of NaBH4 compound*

used for extraction of the final precipitate having a lemon color.

One can suppose the following scheme for the GaP synthesis:

*2.2.3. Synthesis of GaP nanocrystals on the base of Na3P*

The reactions can be expressed as:

tion.

trolling the velocity of its introduction at the moderate heating up to 70°С.

2Ga 6BH 2Ga 3B H 3H

4Ga 4P 4GaP

**Figure 6.** Luminescence of GaP nanoparticles prepared at different conditions (spectra 2-4) and in comparison with the luminescence of perfect GaP bulk single crystals (1). Please see explanations in the text below.

With these results, one can compare the properties of GaP nanoparticles with those of bulk single crystals grown in the 1960s or, approximately, 50 years ago [1-25]. The authors have investigated their optical and mechanical properties [16-25] in the 1960s, 1970s, 1980s and 1990s. Due to a significant number of defects and a highly intensive non-radiative recombi‐ nation of non-equilibrium current carriers, initially luminescence from the freshly prepared undoped crystals could be observed only at the temperatures 80K and below. Today, lumi‐ nescence is clearly detected in the region from 2.0 eV and until 3.0 eV at room temperature (see Figure 6, spectrum 1). Taking into account that the indirect forbidden gap is only 2.25 eV, it is suggested that this considerable extension of the region of luminescence to the high energy side of the spectrum as well as a pronounced increase of its brightness are connected with a very small concentration of defects, considerable improvement of crystal lattice, high transparency of perfect crystals, low probability of phonon emission at rather high tempera‐ ture and participation of direct band-to-band electron transitions.

Our unique collection of long-term-ordered perfect GaP single crystals provides opportuni‐ ties for deep fundamental analogies between perfect single crystals and nanoparticles [29-31] as well as to predict and to realize in nanoparticles and perfect bulk crystals new and interesting properties and applications as the advanced light emissive elements of relevant device structures. More detailed analyses and discussion of these results can be found in the references cited above and will be futher published.

### *2.2.2. Synthesis of GaP nanocrystals on the base of NaBH4 compound*

with dimensions of between 10-100 nm and clear quantum confinement effects but the lumi‐ nescent spectrum was not bright enough and its maximum was only slightly shifted to UV side against the 2.24 eV forbidden gap at room temperature (Figure 6, spectrum 2). The nanoparticles obtained from the reaction with white P at low (125°C) temperature exhibit bright broad band spectra considerably shifted to UV side [27, 28, 36] (Figure 6, spectrum 3, 4). Note that the original powder contains only a part of GaP particles with nearly 10 nm dimension, which develop quantum confinement effect and the relevant spectrum of lumi‐ nescence, so the spectrum of luminescence consists of this band with maximum at 3 eV and of the band characterizing big particles with the maximum close to the edge of the forbidden gap in GaP (Figure 6, spectrum 3), but thorough ultrasonic treatment gives an opportunity to get the pure fraction of nanoparticles with the spectrum 4 having the maximum at 3 eV.

8 Optoelectronics - Advanced Materials and Devices

**Figure 6.** Luminescence of GaP nanoparticles prepared at different conditions (spectra 2-4) and in comparison with

With these results, one can compare the properties of GaP nanoparticles with those of bulk single crystals grown in the 1960s or, approximately, 50 years ago [1-25]. The authors have investigated their optical and mechanical properties [16-25] in the 1960s, 1970s, 1980s and 1990s. Due to a significant number of defects and a highly intensive non-radiative recombi‐ nation of non-equilibrium current carriers, initially luminescence from the freshly prepared undoped crystals could be observed only at the temperatures 80K and below. Today, lumi‐ nescence is clearly detected in the region from 2.0 eV and until 3.0 eV at room temperature (see Figure 6, spectrum 1). Taking into account that the indirect forbidden gap is only 2.25 eV, it is suggested that this considerable extension of the region of luminescence to the high energy side of the spectrum as well as a pronounced increase of its brightness are connected with a very small concentration of defects, considerable improvement of crystal lattice, high transparency of perfect crystals, low probability of phonon emission at rather high tempera‐

Our unique collection of long-term-ordered perfect GaP single crystals provides opportuni‐ ties for deep fundamental analogies between perfect single crystals and nanoparticles [29-31] as well as to predict and to realize in nanoparticles and perfect bulk crystals new and interesting properties and applications as the advanced light emissive elements of relevant

the luminescence of perfect GaP bulk single crystals (1). Please see explanations in the text below.

ture and participation of direct band-to-band electron transitions.

In the method employed here, NaBH4 was used as a deoxidizer during the synthesis in the solvent – toluene, where the sources of Ga and P (white phosphorus) have been dissolved (GaCl3) or suspended. NaBH4 can be used also due to its high solubility in ethanol. The etha‐ nol solution of NaBH4 was introduced into the process of the synthesis during 5 hours, con‐ trolling the velocity of its introduction at the moderate heating up to 70°С.

White-yellow precipitates were the result of the synthesis. The precipitate was rinsed multi‐ ple times in toluene, removing the remaining P and GaCl3, and then in water, removing the water- soluble species such as NaCl. The centrifugal separation from the solvent has been used for extraction of the final precipitate having a lemon color.

One can suppose the following scheme for the GaP synthesis:

$$\begin{aligned} \text{2Ga}\_3 + 6\text{BH}\_4 &\longrightarrow 2\text{Ga} + 3\text{B}\_2\text{H}\_6 + 3\text{H}\_2\\ 4\text{Ga} &+ 4\text{P} \to 4\text{GaP} \\ 4\text{GaCl}\_3 + 12\text{NaBH}\_4 + 4\text{P} &\to 4\text{GaP} + 12\text{NaCl} + 6\text{B}\_2\text{H}\_6 + 6\text{H}\_2 \end{aligned} \tag{3}$$

The last reaction is the closing one, including creation of NaCl, which can be easily removed with deionized water. The main problem of the described synthesis is the exclusion Ga met‐ al particles in the precipitate. The problem is controled via the rate of Ga ion deoxidation, depending on temperature, the types of solvent and deoxidizer. Using low (~1 mL/min) rate of introduction of NaBH4 ethanol solution into the process helps to avoid the metal Ga crea‐ tion.

#### *2.2.3. Synthesis of GaP nanocrystals on the base of Na3P*

For the preparation of Na3P we used elementary Na, white P and the mixture of InCl3/ GaCl3 (4 wt% InCl3 + 96 wt% GaCl3). The main experimental procedures can be described as follows: a 5.2 g mixture of GaCl3 and InCl3 was dissolved in 150 ml of xylene. Then, 2 g of sodium and 0.9 g of white phosphorus were added into the solution. The solution was stirred at 100°C for 10 hrs. After the reaction, the product was filtered for 3 times in xy‐ lene and 3 times in deionized water. The resultant powders were dried in vacuum at 60– 80°C for 2 hrs. All the above mentioned manipulations were conducted in high purity ni‐ trogen (99.999%) atmosphere in a glove box. Lastly, three equal parts of the product was heated respectively to 300°C, 480°C and 600°C for 1 hr in pure nitrogen (99.999%) flows. The reactions can be expressed as:

$$\begin{aligned} \text{6Na} + \text{InCl}\_3 + \text{GaCl}\_3 &= \text{In} + \text{Ga} + \text{6NaCl} \\ \text{In} + \text{P} &= \text{InP} \\ \text{Ga} + \text{P} &= \text{GaP} \end{aligned} \tag{4}$$

According to elaborated by us technology [28, 31] the synthesis of GaP nanocrystals goes in the toluene solvent between dissolved (GaCl3) and dispersed (Na3P) initial chemicals at 80°С under ultrasonic machining for 5 hrs, creating a black-brown precipitate, which must be rinsed multiple times in toluene (removal of P and GaCl3) and water (removal of the soluble matter like NaCl). A high speed centrifuge must be used for separation of the precipitate. The resultant material must not be cleaned; its purity depends only on the pu‐

Advanced Light Emissive Device Structures http://dx.doi.org/10.5772/52416 11

The XRD spectrum of GaP nanocrystals prepared using Na3P and GaCl3 in toluene is pre‐ sented in Figure 7. One can observe the characteristic (111), (220) and (311) reflections for GaP. However, there are some extraneous lines of the low intensity, probably, from NaCl, NaPO3 and showing that purification of GaP nanoparticles was not enough. The extraneous lines of the other than GaP components can be seen also in the spectra of GaP nanoparticles

In conclusion we note that the growth of GaP nanocrystals is the key element in the creation of nanocomposite for advanced device structures because, in spite of the lack of the concrete parameters and conditions of synthesis in the relevant literature sources, all the necessary

Thus, nanoparticles of GaP have been prepared using white P by mild aqueous low temper‐ ature synthesis and 2 methods of colloidal chemistry. The spectra of PL, RLS, and XRD to‐ gether with TEM images of the nanoparticles prepared under different conditions have been compared with each other as well as with those from bulk single crystals, from hydrother‐ mal and colloidal reactions in toluene were presented. Uniform GaP nanoparticles, follow‐ ing ultrasonic treatment yielded a bright luminescence at room temperature with a broad band with maximum at 3 eV and have been used to prepare GaP/polymer nanocomposites.

**3. Development of methods of incorporation of the GaP nanoparticles**

Polyglycidyl methacrylate (PGMA), polyglycidyl methacrylate-co-polyoligoethyleneglycol methacrylate (PGMA-co-POEGMA) and biphenyl vinyl ether (BPVE) polymers were used to synthesize GaP nanocomposites suitable for light emissive luminescent device struc‐ tures. Some other polymers, dielectrics and with high electric conductivity, will be also in‐ vestigated in the process of preparation of this Chapter and used for elaboration of light

Film nanocomposites of good quality with very bright and broad-band luminescence have been prepared. Quality and surface morphology of the nanocomposite films was studied in ambient air using AFM in taping mode on a Dimension 3100 (Digital Instruments, Inc.) micro‐ scope while luminescence of the nanocomposites films deposited by dip-coating from a sus‐ pension in water-ethanol mixture solution on the surface of a silica substrate was excited by the

N2 laser nanosecond pulses at wavelength 337 nm and measured at room temperature.

obtained by the method of Energy Dispersion X-ray Analysis (EDAX).

data for the preparation of GaP nanoparticles are provided herein.

rity of the initial components.

**into polymers**

emissive device structures.

As the result the GaP nanoparticle aggregation was obtained. In a glove box, previously purged with dry nitrogen, 1.2 g of white phosphorus (P4) and 1.7 g of sodium (Na) were placed in 100 mL of distilled dimethylbenzene in an Erlenmeyer flask. The mixture was then stirred, heated to 120°C and maintained at that temperature for 10 hrs. A black fragmented product, Na3P, was obtained. About 10 g of gallium (Ga) pellets were added to a quartz tube with one sealed end. The tube was purged with dry nitrogen and then heated gently. A chlorine gas flow through the melting metal was put in place at a rate until all the gallium reacted. The product - gallium chloride (GaCl3) was formed. In the glove box, 6.5 g of GaCl3 was dissolved in 100 mL of distilled dimethylbenzene in an Erlenmeyer flask. The solution was stirred and heated to 100°C. Then 2.5 g of Na3P was added to the Erlenmeyer flask and the mixture was heated at 100°C with continuous stirring for 2.5 hr. After cooling, the mix‐ ture was filtered and washed with water.

The alternative method for preparation of GaP nanocrystals is interaction of GaCl3 and Na3P:

$$\text{CaCl}\_3 + \text{Na}\_3\text{P} = \text{GaP} \left( \text{nanoparticles} \right) + \text{3NaCl} \tag{5}$$

In this method the stoichiometric ratio of Na (99,9%) and P (99,995%) is placed in the reactor with the Ar inert atmosphere. The reaction of preparation of Na3P goes between melted Na and dispersed white P at 110°C in boiling toluene under intense stirring. This violent reac‐ tion must be supported at the necessary conditions (110°C and intense stirring) for 5 hrs. As the result we have the black suspension of Na3P:

$$\text{CaNa} + \text{P} \rightarrow \text{Na}\_3\text{P} \tag{6}$$

**Figure 7.** XRD spectrum of GaP nanocrystals prepared on the base of Na3P and GaCl3.

According to elaborated by us technology [28, 31] the synthesis of GaP nanocrystals goes in the toluene solvent between dissolved (GaCl3) and dispersed (Na3P) initial chemicals at 80°С under ultrasonic machining for 5 hrs, creating a black-brown precipitate, which must be rinsed multiple times in toluene (removal of P and GaCl3) and water (removal of the soluble matter like NaCl). A high speed centrifuge must be used for separation of the precipitate. The resultant material must not be cleaned; its purity depends only on the pu‐ rity of the initial components.

3 3 6Na InCl GaCl In Ga 6NaCl

As the result the GaP nanoparticle aggregation was obtained. In a glove box, previously purged with dry nitrogen, 1.2 g of white phosphorus (P4) and 1.7 g of sodium (Na) were placed in 100 mL of distilled dimethylbenzene in an Erlenmeyer flask. The mixture was then stirred, heated to 120°C and maintained at that temperature for 10 hrs. A black fragmented product, Na3P, was obtained. About 10 g of gallium (Ga) pellets were added to a quartz tube with one sealed end. The tube was purged with dry nitrogen and then heated gently. A chlorine gas flow through the melting metal was put in place at a rate until all the gallium reacted. The product - gallium chloride (GaCl3) was formed. In the glove box, 6.5 g of GaCl3 was dissolved in 100 mL of distilled dimethylbenzene in an Erlenmeyer flask. The solution was stirred and heated to 100°C. Then 2.5 g of Na3P was added to the Erlenmeyer flask and the mixture was heated at 100°C with continuous stirring for 2.5 hr. After cooling, the mix‐

The alternative method for preparation of GaP nanocrystals is interaction of GaCl3 and Na3P:

In this method the stoichiometric ratio of Na (99,9%) and P (99,995%) is placed in the reactor with the Ar inert atmosphere. The reaction of preparation of Na3P goes between melted Na and dispersed white P at 110°C in boiling toluene under intense stirring. This violent reac‐ tion must be supported at the necessary conditions (110°C and intense stirring) for 5 hrs. As

GaCl Na P GaP nanoparticles 3NaCl 3 3 + = ( ) + (5)

<sup>3</sup> 3Na P Na P + ® (6)

(4)

+ + =+ + + = + =

 In P InP Ga P GaP

ture was filtered and washed with water.

10 Optoelectronics - Advanced Materials and Devices

the result we have the black suspension of Na3P:

**Figure 7.** XRD spectrum of GaP nanocrystals prepared on the base of Na3P and GaCl3.

The XRD spectrum of GaP nanocrystals prepared using Na3P and GaCl3 in toluene is pre‐ sented in Figure 7. One can observe the characteristic (111), (220) and (311) reflections for GaP. However, there are some extraneous lines of the low intensity, probably, from NaCl, NaPO3 and showing that purification of GaP nanoparticles was not enough. The extraneous lines of the other than GaP components can be seen also in the spectra of GaP nanoparticles obtained by the method of Energy Dispersion X-ray Analysis (EDAX).

In conclusion we note that the growth of GaP nanocrystals is the key element in the creation of nanocomposite for advanced device structures because, in spite of the lack of the concrete parameters and conditions of synthesis in the relevant literature sources, all the necessary data for the preparation of GaP nanoparticles are provided herein.

Thus, nanoparticles of GaP have been prepared using white P by mild aqueous low temper‐ ature synthesis and 2 methods of colloidal chemistry. The spectra of PL, RLS, and XRD to‐ gether with TEM images of the nanoparticles prepared under different conditions have been compared with each other as well as with those from bulk single crystals, from hydrother‐ mal and colloidal reactions in toluene were presented. Uniform GaP nanoparticles, follow‐ ing ultrasonic treatment yielded a bright luminescence at room temperature with a broad band with maximum at 3 eV and have been used to prepare GaP/polymer nanocomposites.
