Interpretation of the Yellow Colour of Heat Treated ZnO Powder

Abstract

Two batches of analytical grade ZnO powder (ZnON) are heated to 920 °C and one, (ZnOA), quenched to room temperature, and the other, (ZnOB), cooled slowly. Samples of both ZnOA and ZnOB are afterwards heated for one hour at temperatures between 100 and 800 °C and quenched. From all these samples the amount of free zinc is determined and the reflection and luminescence spectra measured. The reflection spectra with ZnON as blank indicate the presence of a supplementary absorption band having an intensity which depends upon the previous treatment. From this variation and correlation with the amount of free zinc the yellow colour of the samples can be explained and new models for the centres deduced.

Role of oxygen vacancy in metal oxide based photoelectrochemical water splitting

“…These reduced species can not only lead to the EPR response, but also work as color centers and lead to obvious light absorption change. This situation can be found in WO 3, 59 ZnO 60 , TiO 2, 42 ZrO 2 , 29 etc. Moreover, these reduced species can also serve as recombination centers and lead to the obvious photoluminescence (PL) intensity change.…”

“…The density functional theory (DFT) investigation suggests that the V O causes the extend of the O 2p orbital into the forbidden band, therefore narrowing the bandgap 65 . Besides TiO 2 , the V O induced bandgap decrease is also observed in ZnO, 60 In 2 O 3 , 39 and ZrO 2 29 . Therefore, when investigate the role of V O on PEC process, the contribution of extended light harvest should be addressed.…”

Scaling reducibility of metal oxides

“…The band gap and Evac values are rather small compared to the previous irreducible oxides, but it forms F-centers upon creation of an O-vacancy (observed experimentally, see for instance [92][93][94][95][96]), with the corresponding localization of an electron pair in the lattice, together with some delocalization on neighboring Zn sites. The state in the gap only appears when using B3LYP, PBE gives a delocalized picture.…”

Analysis of Urbach-like absorption tails in thermally treated ZnO:Al thin films

“…4-6) as well as a thorough description of the infrared free carrier absorption of the films as a function of N e , mobility l, and carrier scattering mechanisms. 7-10 However, the appearance of absorption tails below the bandgap in ZnO is well known for decades [11][12][13][14][15] but still lacks a detailed theory of its origin. These tails are of great technological interest as they can account for significant absorption of photons with energies less than the bandgap.…”