LUMINESCENCE OF ALKALI OXYFLUOROMOLYBDATES AND OXYFLUOROTUNGSTATES

The luminescence of various sodium or potassium oxyfluorotungstates ha s been investigated. All show at 4K a broad structureless emission ban d whose maximum lies in the 495-570 run range. Like for alkali tungsta tes, quenching of the luminescence of Na3WO3F3, Na5W3O9F5, K2WO2F4 and K2WO2F4.H2O occurs at low temperature. In contrast despite the low en ergy of the emitting state and a weak radiative rate, the emission of Na2WO2F4, like that Of Cs2WO2F4 recently reported, is nearly unaffecte d by non radiative transitions at 300 K, confirming that a fluorine-ri ch environment can lead to a high stability of the tungsten-oxygen cha rge transfer emission. The luminescence of a few oxyfluoromolybdates, NaMoO3F, K2MoO2F4 and K2MoO2F4.H2O, has been examined. The emission li es at longer wavelengths. in the red, and is quenched at low temperatu re.