To verify the effect of crystallinity of the products on UV
emission wavelength, the Room Temperature Photo Lumines-
cence spectra were recorded at the excitation wavelength of
325 nm for the nano ZnO rods A2 and A3 with Xe light as the
excitation source. In Fig. 6, the PL spectrum for synthesized nano
rods A2 and A3 consists of high intense peaks centered at
378.35 nm and 380.34 nm and peaks at 408 nm (NBE).
The PL signal at 400 nm is a typical ZnO UV emission wave-
length [27]. It was observed that the UV emission peaks at
380.34 nm and 408 nm of the A3 rods have higher intensity
(337.3/au and 256/au) compared to those of A2 rods (302.2/au
and 207/au). This also confirms the data obtained from XRD that
A3 rods have high crystallinity. The PL spectrum also has two
weak emission peaks at 474 nm and 518 nm. The UV emission
peak which is also known as near band emission (NBE) could be
attributed to the recombination of free excitons through an
exciton–exciton collision process [28]. The blue transition at
474 nm is caused due to transition from the level of ionized
oxygen vacancy to the valence band. The green emission, called
deep-level emission occurring by the recombination of the photo-
generated holes with singly ionized oxygen vacancies in ZnO, is
centered at 518 nm [29]. As the ratio of the intensity of the NBE
peaks and green emission peaks are high, our ZnO rods synthe-
sized by a microwave assisted simple chemical precipitation
technique have good optical properties [30] and so have less
concentration of oxygen vacancies. Besides, the increased inten-
sity of the deep-level emission in A3 compared to A2 reveals that
the increased concentration of OH ions enhances the surface
defects A3 rod greatly [31].