The effect of doping on luminescent properties of cadmium tungstate

Cadmium Tungstate is a common scintillator crystal used in a variety of commercial and scientific applications. Its relative high density allows for adequate radiation hardness and its low hygroscopicity permits its use at room temperature in harsh environments without the need of moisture protection. The ideal scintillator material is NaI:Tl which is referred as a standard at 100% Charge Collection Efficiency (CCE), but its relative low density and susceptibility to moisture makes its application limited. Cadmium Tungstate efficiency is 30% of NaI:Tl and its radiation damage inhibits peak light output of an additional 40%. The purpose of this study was to understand the characteristics of this reduced efficiency and determine the crystal behaviors under doping conditions of metal ions to increase its peak light output and its resistance to radiation. The use of Combinatorial Materials research was instrumental in segregating thousands of compositions to obtain a stoichiometric balance, which permitted for growth of single crystals. The first step was the preparation of sintered compositions which underwent measurements in a dual system of X-Ray Diffraction and X-Ray Fluorescence to determine the best compositions for increased light output. The second step was to irradiate the corresponding sintered samples under a strong X-Ray flux to determine its radiation damage. Ideally, the best results are determined by a combination of high light output and increased resistance to irradiation damage. The optimized compositions were grown into single crystals according to the Czochralski method and their peak light output measured. Single crystals were irradiated with X-Rays and their radiation resistance was compared to pure and doped sintered CdW04 samples. This study has determined the doping elements and amounts, while maintaining a stoichiometric balance, when added to Cadmium Tungstate achieved a non-precedent doubling of light output and reduced X-Ray damage at room temperatures