**2.1 Preparation of ZnO nanoparticles**

Synthesis of ZnO NPs the different materials were used such as zinc nitrate, urea, glycine, and citric acid. **Table 2** shows the characteristic of the raw materials. The chemical reaction used in synthesis of ZnO powder are given in **Table 3**.

The zinc nitrate hexahydrate and fuel were dissolved in 5 ml of double distilled water and stirred thoroughly to obtain a transparent solution, which was placed inside a preheated muffle furnace at 600°C to initiate the combustion process. Within a short time the mixture ignited with a flame and the rapid evolution of enormous amounts of gases produced a voluminous foamy product (ash). This was ground using an agate pestle and mortar to produce the final powder, without any additional heat treatment. The fuels used in this synthesis have different combination of fuels and shown in **Table 4**.


The synthesis process of ZnO NPs is illustrated in **Figure 1**.

### **Table 2.**

*Characteristics of raw material.*


### **Table 3.**

*Chemical reaction in combustion synthesis of ZnO using different fuels [25].*


### **Table 4.**

*Sample name with respect to used fuels in different combination of fuels.*

**Figure 1.** *Systematic diagram of ZnO synthesized by the combustion method.*

### **2.2 Characterization method**

The prepared ZnO-NPs were characterized by X-ray diffraction (XRD) using advanced Bruker D8 diffractometer with Cu Kα radiation was carried out to check up the crystal structure. The bond characteristics studies using FTIR-8400S. The Optical transmittance spectra were collected using a UV-Vis-IR spectrophotometer (Perkin Elmer, lambda 950). The photoluminescence (PL) data was recorded using 325 nm He-Cd laser system.

## **3. Results and discussion**

### **3.1 X-ray diffraction pattern**

The XRD patterns of the ZnO powders synthesized using mixed fuels is depicted in **Figure 2a** and **b** and are typical of ZnO powders having the hexagonal wurtzite structure (JCPDS 01-036-1451). This indicates that the ZnO was formed directly by the self-propagating high temperature exothermic combustion reaction initiated at moderate temperature. The crystallize size varied from 30 to 70 nm with different fuels contents. UC2 and UG3 show the wurtzite ZnO structure without any impurity peak in the XRD pattern. All three fuels resulted in nanocrystalline powders, but the crystallite size varied significantly with the type of fuel. The effect of the type of fuel, and the F/O ratio in the case of urea, on the properties of the final product also has been studied in our previous research article [25].

### **3.2 Fourier transform infrared spectroscopy (FTIR)**

The FTIR spectrum of ZnO is shown in **Figure 3**. The broad band with very low intensity at 3466 cm<sup>−</sup><sup>1</sup> corresponding to the vibration mode of water OH group indicating the presence of small amount of water adsorbed on the ZnO nanocrystal surface during synthesis. A strong band at 482–455 cm<sup>−</sup><sup>1</sup> is attributed to the Zn-O stretching band. The bond related to C=O and other are shown in **Table 5**.

**19**

**Figure 3.**

**Figure 2.**

*Structural and Luminescence Properties of ZnO Nanoparticles Synthesized by Mixture of Fuel…*

The UV-Vis reflectance spectra of the ZnO nanomaterial synthesized using different fuels are shown in the inset of **Figure 4a** and **b***,* and the corresponding absorbance spectra are calculated using the Kubelka-Munk function [26]:

*<sup>K</sup>* <sup>=</sup> (1 <sup>−</sup> *<sup>R</sup>*)<sup>2</sup> \_\_\_\_\_\_ <sup>2</sup>*<sup>R</sup>* (1)

where K is the reflectance transformed according to Kubelka-Munk, h is Planck constant, is the light frequency, and R is reflectance (%). The relevant increase in the absorption at wavelengths less than 400 nm can be assigned to the optical band-gap absorption of ZnO due to changes in their morphologies, particle size and surface microstructures or the quantum confinement effect [27, 28]. The absorption edges are change with fuels as taken to synthesis ZnO. ZnO has a direct transition

*XRD pattern: (a) ZnO with mixed fuel (urea + citric acid) and (b) ZnO with mixed fuel (urea + glycine).*

*FTIR spectrum: (a) ZnO with mixed fuel (urea + citric acid) and (b) ZnO with mixed fuel (urea + glycine).*

*DOI: http://dx.doi.org/10.5772/intechopen.82467*

**3.3 UV-Visible absorption spectrum**

*Structural and Luminescence Properties of ZnO Nanoparticles Synthesized by Mixture of Fuel… DOI: http://dx.doi.org/10.5772/intechopen.82467*

### **3.3 UV-Visible absorption spectrum**

*Zinc Oxide Based Nano Materials and Devices*

**2.2 Characterization method**

*Systematic diagram of ZnO synthesized by the combustion method.*

**Figure 1.**

325 nm He-Cd laser system.

**3. Results and discussion**

**3.1 X-ray diffraction pattern**

intensity at 3466 cm<sup>−</sup><sup>1</sup>

The prepared ZnO-NPs were characterized by X-ray diffraction (XRD) using advanced Bruker D8 diffractometer with Cu Kα radiation was carried out to check up the crystal structure. The bond characteristics studies using FTIR-8400S. The Optical transmittance spectra were collected using a UV-Vis-IR spectrophotometer (Perkin Elmer, lambda 950). The photoluminescence (PL) data was recorded using

The XRD patterns of the ZnO powders synthesized using mixed fuels is depicted in **Figure 2a** and **b** and are typical of ZnO powders having the hexagonal wurtzite structure (JCPDS 01-036-1451). This indicates that the ZnO was formed directly by the self-propagating high temperature exothermic combustion reaction initiated at moderate temperature. The crystallize size varied from 30 to 70 nm with different fuels contents. UC2 and UG3 show the wurtzite ZnO structure without any impurity peak in the XRD pattern. All three fuels resulted in nanocrystalline powders, but the crystallite size varied significantly with the type of fuel. The effect of the type of fuel, and the F/O ratio in the case of urea, on the properties of the final

The FTIR spectrum of ZnO is shown in **Figure 3**. The broad band with very low

indicating the presence of small amount of water adsorbed on the ZnO nanocrystal

stretching band. The bond related to C=O and other are shown in **Table 5**.

corresponding to the vibration mode of water OH group

is attributed to the Zn-O

product also has been studied in our previous research article [25].

**3.2 Fourier transform infrared spectroscopy (FTIR)**

surface during synthesis. A strong band at 482–455 cm<sup>−</sup><sup>1</sup>

**18**

The UV-Vis reflectance spectra of the ZnO nanomaterial synthesized using different fuels are shown in the inset of **Figure 4a** and **b***,* and the corresponding absorbance spectra are calculated using the Kubelka-Munk function [26]:

$$K = \frac{\left(\frac{\mathbf{1}}{\cdot} - R\right)^2}{2R} \tag{1}$$

where K is the reflectance transformed according to Kubelka-Munk, h is Planck constant, is the light frequency, and R is reflectance (%). The relevant increase in the absorption at wavelengths less than 400 nm can be assigned to the optical band-gap absorption of ZnO due to changes in their morphologies, particle size and surface microstructures or the quantum confinement effect [27, 28]. The absorption edges are change with fuels as taken to synthesis ZnO. ZnO has a direct transition

**Figure 2.** *XRD pattern: (a) ZnO with mixed fuel (urea + citric acid) and (b) ZnO with mixed fuel (urea + glycine).*


### **Table 5.**

*Chemical boding characteristics of synthesized ZnO with mixed fuels.*

### **Figure 4.**

*Absorbance spectra with reflectance insect: (a) ZnO with mixed fuel (urea + citric acid) and (b) ZnO with mixed fuel (urea + glycine).*

and the corresponding bandgaps for different mixed fuels shown in **Figure 5a** and **b** respectively are calculated from a Tauc plot of (*αhν*) 2 versus the photon energy (*hν*). These bandgap values blue shifted little 3.08 to 3.2 eV relative to the zinc oxide nanomaterial.

### **3.4 Photoluminescence study**

The photoluminescence properties of semiconductor materials undergo change when their size gets down to nanometer scale known as the quantum size effects. The photoluminescence originates from the recombination of surface states. **Figure 6a** and **b** shows the photoluminescence spectra of ZnO powder synthesis by different fuels with excitation wavelength of 325 nm at room temperature. The spectra exhibits two emission peaks, One is located at around 384 nm (UV region)

**21**

maximum defect related emission.

**4. Conclusions**

**Figure 5.**

**Figure 6.**

*Structural and Luminescence Properties of ZnO Nanoparticles Synthesized by Mixture of Fuel…*

*Energy bandgap: (a) ZnO with mixed fuel (urea + citric acid) and (b) ZnO with mixed fuel (urea + glycine).*

corresponding to the near-band-edge emission [29] which originates from free exciton emission and the other peak corresponding to ionized oxygen vacancies [30] with change for different fuels. High intensity oxygen vacancies peak at 632 nm is obtained for ZnO nanoparticle synthesis by urea with citric acid and band to band peak is eliminate. UC2 shows maximum band edge intensity and ZG3 shows

*PL spectra (a) ZnO with mixed fuel (Urea + Citric acid) (b) ZnO with mixed fuel (urea+glycine).*

ZnO nanomaterials were successfully synthesized by the combustion method using different fuels ratio. The XRD patterns were consistent with polycrystalline ZnO having the hexagonal wurtzite structure. The ZnO NPs size changed for different fuels with the minimum crystallite size of 26–40 nm obtained by using Glycine, citric acid with Urea at different ratio. The chemical band study shows that OH group has least intensity at higher Urea content. There is little change observed in bandgap with different fuel contents. In the ZnO powder synthesized with different

*DOI: http://dx.doi.org/10.5772/intechopen.82467*

*Structural and Luminescence Properties of ZnO Nanoparticles Synthesized by Mixture of Fuel… DOI: http://dx.doi.org/10.5772/intechopen.82467*

**Figure 5.** *Energy bandgap: (a) ZnO with mixed fuel (urea + citric acid) and (b) ZnO with mixed fuel (urea + glycine).*

**Figure 6.**

*Zinc Oxide Based Nano Materials and Devices*

Stretching vibration of

C-H in plane bending

Zn-O

vibration

**Table 5.**

**Functional group Wavenumber (cm<sup>−</sup><sup>1</sup>**

Bending mode of carbonate 823–910 — 863 839 815 831 Stretching vibration of C-O 1031 — 1025 1001 1098 —

Bending vibration of –CH2 1374 — 1349 1382 1382 1374 C=O band 1536 1582 1585 1544 1625 1617 Carboxyl group 1925 — — 1917 1917 1917 Existence of CO2 2428 — — 2201–2355 2363 — O-H stretching of water 3466 3441 3473 3466 3466 3457

and the corresponding bandgaps for different mixed fuels shown in **Figure 5a** and **b**

*Absorbance spectra with reflectance insect: (a) ZnO with mixed fuel (urea + citric acid) and (b) ZnO with* 

(*hν*). These bandgap values blue shifted little 3.08 to 3.2 eV relative to the zinc oxide

The photoluminescence properties of semiconductor materials undergo change when their size gets down to nanometer scale known as the quantum size effects. The photoluminescence originates from the recombination of surface states. **Figure 6a** and **b** shows the photoluminescence spectra of ZnO powder synthesis by different fuels with excitation wavelength of 325 nm at room temperature. The spectra exhibits two emission peaks, One is located at around 384 nm (UV region)

2

versus the photon energy

**)**

**ZC1 ZC2 ZC3 ZG1 ZG2 ZG3**

1163 — — — — —

482 482–555 482 482 482–547 482–547

respectively are calculated from a Tauc plot of (*αhν*)

*Chemical boding characteristics of synthesized ZnO with mixed fuels.*

**20**

nanomaterial.

*mixed fuel (urea + glycine).*

**Figure 4.**

**3.4 Photoluminescence study**

*PL spectra (a) ZnO with mixed fuel (Urea + Citric acid) (b) ZnO with mixed fuel (urea+glycine).*

corresponding to the near-band-edge emission [29] which originates from free exciton emission and the other peak corresponding to ionized oxygen vacancies [30] with change for different fuels. High intensity oxygen vacancies peak at 632 nm is obtained for ZnO nanoparticle synthesis by urea with citric acid and band to band peak is eliminate. UC2 shows maximum band edge intensity and ZG3 shows maximum defect related emission.

### **4. Conclusions**

ZnO nanomaterials were successfully synthesized by the combustion method using different fuels ratio. The XRD patterns were consistent with polycrystalline ZnO having the hexagonal wurtzite structure. The ZnO NPs size changed for different fuels with the minimum crystallite size of 26–40 nm obtained by using Glycine, citric acid with Urea at different ratio. The chemical band study shows that OH group has least intensity at higher Urea content. There is little change observed in bandgap with different fuel contents. In the ZnO powder synthesized with different fuels using glycine the band to band PL peak intensity was negligible compared to the defect related emission.
