Controlled synthesis and photoluminescence behaviors of Lu2O2SO4:Eu3+ and Lu2O2S:Eu3+ phosphors

Abstract

A “general” amorphous precursor that can synthesize Eu3+ doped Lu2O2SO4 and Lu2O2S phosphors was prepared from commercially available Lu2O3 (AR), HNO3 (99.95% purity), (NH4)2SO4 (AR) and NH3·H2O (99.95% purity) as raw materials via a facile co-precipitation method. Based on this, block-like Lu2O2SO4:Eu3+ phosphors were synthesized by calcination in air, and mixed structures of near-spherical and rod-like Lu2O2S:Eu3+ phosphors were synthesized by calcination in a confined sulfuration atmosphere created using a solid-state method. Studies have shown that the molar ratio of SO42−:Lu3+ and the aqueous ammonia titration volume is very important in the co-precipitation process, the optimal ratio was selected as 25:1, and the optimal 1.5 M NH3·H2O solution volume was selected as 22 mL in this study. In the subsequent calcination process, the effect of calcination temperature on the target product was studied. The optimal calcination conditions are a calcination temperature of 800 °C for 2 h in air and 500 °C for 2 h in a closed sulfuration atmosphere, respectively, for the oxysulfate and oxysulfide phosphors. The photoluminescence (PL) behavior of the two phosphors was systematically investigated. The oxysulfate and oxysulfide phosphors show the characteristic red-light emission of the Eu3+ ion at about 620 and 628 nm, respectively, which originates from the 5D0-7FJ (J = 0,1,2,4) transition of the Eu3+ ion. The luminescence quenching types of both phosphors were dominated by exchange interactions and the optimum Eu3+ molar concentrations were found to be 3.0% for Lu2O2SO4:Eu3+ and 6.0% for Lu2O2S:Eu3+. The oxysulfide phosphor had a PL intensity ∼2.15 times stronger than the oxysulfate phosphor. The CIE color coordinates of the Lu2O2SO4:Eu3+ and Lu2O2S:Eu3+ phosphors are (0.6551, 0.3444) and (0.5842, 0.413), which belong to the categories of reddish-orange and orange colors, respectively. A shorter fluorescence lifetime (∼12.650 μs) and CCT (1738 K) was observed for the oxysulfide phosphor relative to those of the oxysulfate phosphor (∼377.956 μs and 2787 K).