Fluorescence properties of divalent and trivalent europium ions in CdWO4 single crystals grown by the Bridgman method

Optical absorption,excitation,and fluorescence were investigated in Eu ion-doped CdWO4 single crystal grown by a modified Bridgman method.The results indicate that Eu2+ and Eu3+ ions coexist in CdWO4 crystal and an energy transfer occurs between these Eu2+ and Eu3+ ions.When the crystal is excited by 266-nm light,the energy corresponding to the 4f65d to 8S7/2 transition of Eu2+ ions results in the excitation of the Eu3+ ions to the 5DJ level.The effect on fluorescence of annealing in oxygen at various temperatures was investigated.The excitation intensity of Eu2+ ions at 266 nm decreases as annealing temperature increases from 300 K to 1073 K,but it remains at a certain equilibrium level when the annealing temperature is further increased.