Effect of heat treatment on photoluminescence behavior of Zn2SiO4 :Mn phosphors

Thermal treatment in reducing atmospheres gives rise to an increase both in emission intensity and 10% decay time in Zn2SiO4:Mn phosphors. In this study, Zn2SiO4:Mn phosphors were fired in air and then thermally treated in two different reducing atmospheres (hydrogen or carbon). The photoluminescent (PL) behaviour was closely related to the X-ray absorption data. XANES and EXAFS indicated that the oxidation state (+2) remains identical regardless of whether or not the samples are treated, but that the Mn-O distance is reduced by the heat treatment. In order to give a plausible interpretation to the change in PL results, two possible suggestions are presented. Firstly, it is conceivable that the thermally activated diffusion process of manganese ions splits the Mn-Mn pair during the heat treatment. Another possibility is that the annealing produces quenching sites, which are related with defects and impurities. Such hypotheses can be rationalised systematically by considering the results from lifetime measurements, Debye-Waller factor calculations, and XANES pre-edge peaks. 26 refs.