Effects of Annealing on Calcium Tungstate Crystals

The influence of annealing in different atmospheres on absorption and luminescent properties of high-quality undoped CaWO₄ single crystals is presented. The decreasing of green emission intensity after annealing in oxygen and air have been revealed, while two well-defined maxima near 25,000 and 32,000cm^-1 can be observed in the induced absorption spectra. These maxima are attributed to the interstitial oxygen, possibly in the form of the O⁻-centre. The increase of the blue/green luminescence ratio has been revealed after annealing in nitrogen while the crystal transparency remains unaffected. The possible ways to reduce slow green emission component without changing crystal absorption are shown. Structure of colour centres and the models of revealed processes are discussed.

 

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