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

The sulfate-type layered hydroxides of (Gd1-xTbx)(2)(OH)(5)(SO4)(0.5<bold>)nH(</bold>2)O (x=0.06-0.10) have been directly crystallized via hydrothermal reaction at 120 degrees C and pH similar to 10.0, without the need of conventional anion exchange. The primary crystallites were found to be thin platelets having lateral sizes of similar to 450-1000nm and thicknesses of similar to 65-85nm. Combined analysis by DTA/TG, FTIR, and XRD revealed that the layered compounds convert into cubic (Gd1-xTbx)(2)O-3 solid-solutions through dehydration, dehydroxylation, and desulfuration up to similar to 1200 degrees C and via a (Gd1-xTbx)(2)O-2.5(SO4)(0.5) intermediate phase. Optical spectroscopies found that the layered compounds and the derived oxides have their strongest 4f(8)4f(7)5d(1) transition excitations at similar to 248 and 305nm and optimal Tb3+ contents of 9at.% (x=0.09) and 8at.%, respectively. Both the types of materials exhibit the strongest emission at similar to 544nm (the (D4F5)-D-5-F-7 transition of Tb3+), but the oxide has an emission intensity similar to 3 times that of the hydroxide. Fluorescence lifetime of the 544nm green emission was found to decrease from 2.45 to 2.15ms along with increasing Tb3+ content for the oxide, and smaller values of similar to 1.55ms were derived for the layered hydroxides.