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

The thermal treatment in reducing atmospheres gives rise to the increase both in emission intensity and 10% decay time in Zn2SiO4:Mn phosphors. The present investigation aims to take account of such changes in association with the structural change. For this sake, X-ray absorption spectroscopy techniques such as XANES and EXAFS were conducted to the Zn2SiO4:Mn phosphors. The Zn2SiO4:Mn phosphors were fired in the air and then thermally treated in two different reducing atmospheres (hydrogen or carbon). The photoluminescent (PL) behavior was closely related to the X-ray absorption data. The XANES and EXAFS prove that the oxidation state (+2) remains identical regardless of whether or not the samples are treated, but that the Mn–O distance was 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 Mn–Mn pair during the heat treatment. Another possibility is that the thermal treatment annealed out some quenching site, which is related with defects and impurities. Such hypotheses can be rationalized systematically by considering the results from lifetime measurement, Debye–Waller factor calculation, and XANES pre-edge peaks.