X-ray and ultraviolet luminescence of Li3Ta1-xNbxO4 prepared by flux synthesis and characterization of a new high efficiency X-ray phosphor

The phase development and luminescence properties, under both X-ray and ult raviolet excitation, of the lithium orthotantalate-lithium orthoniobate sys tem, Li3Ta1-xNbxO4 for x = 0 to 1, mere examined. Using a flux synthesis te chnique, it was found that the levels of Nb-doping in monoclinic Li3TaO4 an d of Ta-doping in cubic Li3NbO4 are higher than previously reported. Under 30 kVp molybdenum X-ray excitation, Li3Ta1-xNb4O4 is an efficient blue-emit ting phosphor with broadband emission, peaking in the range of 390 to 435 n m. For x = 0 to 0.1, the overall luminescence efficiency is comparable to, or better than, a commercial calcium tungstate, CaWO4, Hi-Plus material. Th e composition Li3Ta0.995Nb0.005O4 demonstrates an overall luminescence effi ciency that makes this phosphor 45% brighter than CaWO4 Hi-Plus, thereby ma king it a potentially attractive candidate for use in medical diagnostic im aging systems. Under ultraviolet excitation, broadband blue emission is als o observed. For all the Li3Ta1-xNbxO4 (x > 0) solid solutions, the emission peak maximums agree well with those seen under X-ray excitation and are th e result of Nb5+ emission. (C) 1999 Academic Press.