The effect of site occupation and valence state of Bi on the luminescence properties of Bi-activated oxysulfide MZnOS (M = Ca, Ba) with layer structure

A novel blue-green-emitting and red-emitting phosphor MZnOS: Bi, Li (M = Ca, Ba) have been prepared, and the correlation between site occupation, valence state of Bi in MZnOS and their luminescence properties was investigated. In MZnOS, M sites are the most suitable and stable sites for Bi to occupy according to the Rietveld refinement and first principle calculation. Bi is found to be in trivalent state in CaZnOS, but is a mixture of divalent and trivalent states in BaZnOS. Under 366 nm excitation, Bi - doped CaZnOS and BaZnOS show strongly broad emission bands with the peak at about 485 and 507 nm, respectively, attributing to the 3P1,0 → 1S0 transition of Bi3+. However, another broad band emission with the peak at 627 nm is observed for BaZnOS: Bi, Li upon 297 nm excitation. The X-ray excited luminescence (XEL) of Bi in MZnOS exhibit the similar properties as observed under UV excitation. The thermal stability of MZnOS: Bi, Li is relatively good enough for practical application. MZnOS: Bi, Li show potential applications as blue-green and red emission phosphor for LED devices considering the suitable absorption and emission wavelength range, high stability, as well as low cost.