## 3 Results
### UV-Vis Diffuse Reflectance  
The diffuse reflectance spectra of all the samples are shown in Figure 6a-c. The spectra can be categorised into three domains: (a) as a function of temperature as per the discussion in Section 3.1 of samples A01-A04 (Figure 6a); (b) as a function of small change in ZnO concentration as discussed in Section 3.2 for samples A05 to A07 (Figure 6b); and (c) as a function of large change in ZnO concentration as discussed in Section 3.3 for samples A08 to A10 (Figure 6c). The results of sample A02 are also shown in all three graphs for comparison.  
For sample A01, the UV-Visible diffuse reflectance spectra show a single broad absorption with a maximum at \(\sim\)375 nm. In this sample, we noticed several reflections in the pXRD pattern. For samples A02 to A04, the main UV-Visible absorption maximum is observed at 300 nm along with a shoulder at \(\sim\)375 nm. Upon decreasing the ZnO concentration in small steps [Figure 6a], the major change is observed in the 375 nm band,  
Figure 5: (**a–e**) FE-SEM micrographs for different samples at different temperatures, i.e., 700, 800, 900, 1000 \({}^{\circ}\)C and 800 \({}^{\circ}\)C, respectively; (**f**) EDS spectra of sample A02, and (**g**) EDS spectra of sample A10. The relative compositions for the two samples are shown in the inset of (**f**,**g**).  
Figure 6: The UV-Vis-NIR patterns for samples containing different temperatures and concentrations of ZnO for samples, (**a**) A1 to A4; (**b**) A2 and A5 to A7; and (**c**) A2 and A8 to A10.  
whose intensity decreases with a decrease in the ZnO concentration. The present UV-Visible diffuse reflectance results are in good agreement with the pXRD patterns, where similar observations could be made. Similar results are obtained when the ZnO concentration decreases in larger steps [Figure 6c]. We observe that the intensity of the shoulder peak at 375 nm decreases and is almost negligible for sample A10, similar to the pXRD pattern. The pXRD and UV-Vis reflectance results are found to be in good agreement with each other.  
When we investigate the literature for information regarding the type of bandgap of Zn\({}_{2}\)TiO\({}_{4}\), we observe varied information. In ref. [16] on Zn\({}_{2}\)TiO\({}_{4}\) films, the material is mentioned to be a direct band gap semiconductor with an optical band gap energy of 3.09 eV (400 nm). However, in another article, it is mentioned to be indirect in nature with an optical band gap of 3.29 eV (376 nm) [17]. In our results, we also observe a band at 375 nm similar to these reports. However, this band disappears when the concentration of ZnO decreases, suggesting that the band gap can be modulated without affecting the crystallinity of the host matrix. In one of the articles by [PERSON] et al. [18], it is mentioned that the band gap of Zn\({}_{2}\)TiO\({}_{4}\) with the highest crystal quality is 4.41 eV (282 nm). When we compare this observation with our results, where we also obtain a band gap maximum in the same wavelength region for sample A10, we infer that the band gap of Zn\({}_{2}\)TiO\({}_{4}\) could be \(\sim\)4.40 eV, and the band at 3.30 eV as reported in earlier findings could be a result of unreacted ZnO in the host lattice.