Effects of tungsten source and tartrate additive on the microstructure and photoluminescence of hydrothermally crystallized ZnWO4

Abstract

Tungstate source and tartrate (Tar2−) additive were examined for their influences on the hydrothermal formation and characteristics of ZnWO4 nanocrystals. It was clearly shown that quasi-equiaxed nanocrystallites of ~ 50–100 nm in diameter and nanorods of ~ 40–50 nm in diameter and up to ~ 700 nm in length can be generated with (NH4)10W12O41·5H2O and K2WO4·2H2O as tungsten sources, respectively. Introducing Tar2− into the K2WO4·2H2O reaction system effectively transformed the primary crystallites of ZnWO4 from nanorods into quasi-equiaxed nanocrystals (~ 20–50 nm) and then nanoplates (thickness of ~ 20 nm, lateral size of ~ 200 nm) and, meanwhile, aggregated the crystallites into spheroidal clusters (~ 2–3 µm in diameter) with the increasing Tar2−/Zn2+ molar ratio up to ~ 2. Optical spectroscopy revealed that the ZnWO4 products exhibit broad-band photoluminescence (~ 425–700 nm) through 3T1u → 1A1g transition of the [WO6]6− ligand under short ultraviolet excitation and the nanorods show the best luminescence among all tested samples. Calcination at 500 °C may effectively remove the adsorbed Tar2− species and greatly improve luminescence of the samples synthesized in the presence of Tar2−.