**3.4 Energy dispersive X-ray analysis (EDX)**

Elemental investigation of the prepared samples is generally determined by EDX analysis. The spectrum shows the relation between the X-ray energy, which lies in between 10 and 20 eV, and the number of counts per channel by a plot between them in X and Y axes, respectively. An X-ray line is expanded by the reaction of the framework, delivering a Gaussian profile. Energy resolution is characterized as the full width of the crest at half maximum height (FWHM). In the spectrum of both the Gd2O3 samples, intense peak of Gd and O is present, which confirms the formation of Gd2O3 phosphor (**Figure 6**). For EDX analysis, the entire area of the black and white SEM micrographs was analyzed with EDX mapping and spectrum. The

### **Figure 5.**

*Transmission electron microscope image of Gd2O3 phosphor: (A) glycerin fuel and (B) urea fuel.*

**Figure 6.** *EDX spectra of Gd2O3 phosphor: (A) glycerin fuel and (B) urea fuel.*

EDX mapping measurements were carried Gd2O3 powders to analyze the composition of the clustered particles [1, 2].
