**3.7 Photoluminescence spectra and CIE diagrams of Gd2O3 phosphors**

The emission spectra of Gd2O3 phosphor prepared with both the fuels have emission peaks at UV and visible region. A slight variation in peaks was observed in emission peaks for both phosphors. The emission spectra of Gd2O3 phosphor prepared by combustion synthesis method have peak at UV region in between 317 and 399 nm along with weak blue band around 450–494 nm, green around 515–586 nm, and red emission centered at 616–625 nm (**Figure 9**).

**Figure 7.** *The Gd (3d) XPS spectrum of Gd2O3 nanocrystals (reproduced from [1]).*

### *Rare Earth Elements and Their Minerals*

6 P7/2 → <sup>8</sup> S7/2 transition is responsible for the UV emission centered at 317 nm, whereas the visible emissions are due to transition from <sup>6</sup> GJ state of Gd3+ [8]. The presence of oxygen vacancy and interstitials also contributes in modified photoluminescence response for oxide-based system [8]. Transition from <sup>6</sup> GJ state of Gd3+ ion and <sup>6</sup> GJ/ 6 PJ transition is responsible for green and red emissions, respectively (**Figure 10**).

To determine the specific color produced by the prepared Gd2O3 phosphor, CIE coordinate diagram was prepared by using MATLAB 7.10.0 (R2010a) software. The CIE coordinates for combustion synthesized Gd2O3 phosphor were found *X* = 0.207 and *Y* = 0.206, which resemble with blue color. Effect of annealing on the produced color was determined by the CIE coordinates of Gd2O3 phosphor annealed at 900°C. It was observed that the *X* and *Y* coordinates for the annealed sample have same values as freshly prepared samples, and only the change in intensity was observed after annealing (**Figure 9**) [9].

**Figure 8.** *Raman spectra of Gd2O3 nanoparticles (reproduced from [1]).*

**85**

second-order kinetics (**Table 2**).

at 6 Cs<sup>−</sup><sup>1</sup>

**Figure 10.**

*Gd2O3: A Luminescent Material*

*DOI: http://dx.doi.org/10.5772/intechopen.92310*

**3.8 Thermoluminescence study of pure Gd2O3 phosphor**

*Energy level diagram for emission transitions for pure Gd2O3 phosphor (reproduced from [7]).*

for urea and glycine fueled phosphors, respectively [10].

The TL response of the Gd2O3 phosphor was recorded under 254 nm UV exposure and 60Co gamma exposure for the phosphors prepared by both urea and glycine fuel. The TL glow curve of phosphors prepared with both the fuels was recorded under 254 nm UV exposure immediately after 5 min exposure time at 6 Cs<sup>−</sup><sup>1</sup>

heating rate, the TL glow peak was found at 232°C and 221°C (**Figure 11**)

rate. For the combustion synthesized phosphor, the TL glow peak was found at 103°C and 111°C for urea and glycine fuels, respectively. For 1 kGy gamma exposure

Chen's peak shape method was used to determine all the kinetic parameters including order of kinetic, activation energy, shape factor, and so on [4–6, 11] (**Table 1**). The activation energy for TL glow curve for combustion synthesized both phosphors has 0.66 eV for UV exposure and 0.71 and 0.72 eV for gamma exposure. Due to gamma exposure, deeper traps were formed, which are responsible for the higher activation energy value. The phosphor follows second-order kinetics as the obtained shape factor value for UV exposure and gamma exposure was in the range of 0.49–0.52 and 0.50–0.54, respectively, which is near to 0.52 for

heating

**Figure 9.** *Emission spectra of pure Gd2O3 phosphor: (A) urea and (B) glycerin (reproduced from [7]).*

*Rare Earth Elements and Their Minerals*

observed after annealing (**Figure 9**) [9].

*Raman spectra of Gd2O3 nanoparticles (reproduced from [1]).*

*Emission spectra of pure Gd2O3 phosphor: (A) urea and (B) glycerin (reproduced from [7]).*

whereas the visible emissions are due to transition from <sup>6</sup>

minescence response for oxide-based system [8]. Transition from <sup>6</sup>

S7/2 transition is responsible for the UV emission centered at 317 nm,

To determine the specific color produced by the prepared Gd2O3 phosphor, CIE coordinate diagram was prepared by using MATLAB 7.10.0 (R2010a) software. The CIE coordinates for combustion synthesized Gd2O3 phosphor were found *X* = 0.207 and *Y* = 0.206, which resemble with blue color. Effect of annealing on the produced color was determined by the CIE coordinates of Gd2O3 phosphor annealed at 900°C. It was observed that the *X* and *Y* coordinates for the annealed sample have same values as freshly prepared samples, and only the change in intensity was

PJ transition is responsible for green and red emissions, respectively

presence of oxygen vacancy and interstitials also contributes in modified photolu-

GJ state of Gd3+ [8]. The

GJ state of Gd3+

6 P7/2 → <sup>8</sup>

ion and <sup>6</sup>

(**Figure 10**).

GJ/ 6

**84**

**Figure 9.**

**Figure 8.**

**Figure 10.**

*Energy level diagram for emission transitions for pure Gd2O3 phosphor (reproduced from [7]).*
