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Up-conversion luminescence of ytterbium and thulium codoped potassium yttrium double tungstate crystalThulium and ytterbium co-doped double tungstate Yb 3+ ,Tm 3+ : NaY(WO 4 ) 2 single crystals were prepared by using RF-heating Czochralski (CZ) pulling method. Its polarized transmittance spectra have been recorded in the region of 290-2000nm at room temperature. The energy levels transitions were assigned to the corresponding absorption line. The up-conversion luminescences at 793nm and 475nm w ere measured when the sample were pumped by 972nm LD and the energy transfer mechanism between Yb 3+ and Tm 3+ ions was analyzed.

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