Direct Crystallization of Sulfate-Type Layered Hydroxide, Derivation of (Gd,Tb)2O3 Green Phosphor, and Photoluminescence.

The sulfate-type layered hydroxides of (Gd1− xTb x)2( OH)5( SO4)0.5· nH2O ( x = 0.06-0.10) have been directly crystallized via hydrothermal reaction at 120°C and pH ~10.0, without the need of conventional anion exchange. The primary crystallites were found to be thin platelets having lateral sizes of ~450-1000 nm and thicknesses of ~65-85 nm. Combined analysis by DTA/ TG, FTIR, and XRD revealed that the layered compounds convert into cubic (Gd1− xTb x)2O3 solid-solutions through dehydration, dehydroxylation, and desulfuration up to ~1200°C and via a (Gd1− xTb x)2O2.5( SO4)0.5 intermediate phase. Optical spectroscopies found that the layered compounds and the derived oxides have their strongest 4 f8→4 f75 d1 transition excitations at ~248 and 305 nm and optimal Tb3+ contents of 9 at.% ( x = 0.09) and 8 at.%, respectively. Both the types of materials exhibit the strongest emission at ~544 nm (the 5D4→7F5 transition of Tb3+), but the oxide has an emission intensity ~3 times that of the hydroxide. Fluorescence lifetime of the 544 nm green emission was found to decrease from 2.45 to 2.15 ms along with increasing Tb3+ content for the oxide, and smaller values of ~1.55 ms were derived for the layered hydroxides. [ABSTRACT FROM AUTHOR]