Photo- and radioluminescent properties of undoped and Bi-doped Lu2WO6 powders at 10–300 K

Abstract

Undoped and Bi3+-doped lutetium oxytungstate (Lu2WO6) powder materials were prepared by a solid state reaction method at selected temperatures between 1000 and 1400°C. The structural, radio- and photoluminescent properties of these materials were investigated. Upon Bi activation, red-shifts of both emission and excitation bands are observed. While a broad emission band characteristic of undoped Lu2WO6 and resulting from a charge transfer transition of the tungstate group WO6 peaks at 450nm, the Bi3+-activated Lu2WO6 shows a broad band emission peaking at about 510nm. This emission can be related to the transition between excited and ground states of a deep Bi donor. The ground state of this donor corresponds to an electron-occupied Bi-level at about 0.45eV above the top of the valence band. Both compositions generate bright radioluminescence upon X-ray excitation at low temperatures. For Lu2WO6:Bi the radioluminescence efficiency is roughly stable in the range between 10 and 250K, while undoped Lu2WO6 suffers from moderate thermal quenching above 10K. The fraction of total radioluminescence due to Bi contribution in Lu2WO6:Bi increases from 0.19 at 10K to 0.53 at room temperature. A simple configuration coordinate diagram is introduced in order to illustrate and describe the charge carrier recombination and light generation mechanism in these materials.