Growth And Optical Properties Of Tm, Eu Doped CdWO₄Single Crystals

It is well known that CdWO₄single crystals are largely studied as competitive host materialsin the optical field due to their promising applications for laser, scintillators and other opticalmaterials. Previous studies showed that W6+site in the CdWO₄easily replaced by cation with highvalence state and Cd²⁺site is readily replaced by cation with low valence state. The opticalproperties of CdWO₄can be largely improved when it was doped with different rare earth ions.This paper was used Bridgman method to get two different single crystals, and their opticalproperties have been measured. The detailed results as following.Firstly, the high quality of Tm³⁺:CdWO₄single crystal in the size of～Φ25×90mmhas been grown by Bridgman method under the technical condition of choosing CdO:WO3:Tm2O3raw chemical composition in molar ratio of1:1:0.005, the gradient temperature of solid-liquid interface is～50°C and growth rate of0.5mm/h. The X-ray diffraction （XRD）, absorption,excitation and emission spectra of different part of the Tm³⁺:CdWO₄crystals wereinvestigated unannealed and annealed. The results suggest that Tm³⁺can replaced Cd²⁺and getTm³⁺:CdWO₄single crystal. It is obvious that the absorption spectrum is characterized by twobroad and strong optical absorption bands at wavelengths of about472nm and708nm, Twosmall sharp absorption peaks at684and805nm were observed, which are corresponding to thetransitions3H6â†'3F3and3H6â†'3H4. The emission spectra of single crystal were also investigatedunder excited by808nm at room temperature. A strong emission band at1.47and1.50μm, and aweak band at1800nm were observed, which they are corresponding to the3H4â†'3F4and3F4â†'3H6transitions of Tm+3, respectively.The Eu²⁺/Eu³⁺:CdWO₄single crystal with good optical quality in the size of25×100mm has been grown by Bridgman method under the technical condition of choosingCdO:WO3:Eu2O3raw chemical composition in molar ratio of1:1:0.005, temperature gradient ofsolid-liquid interface controlling～40°C and10mm/d growth rate. Optical absorption, excitationand fluorescence were investigated. The results indicated that Eu²⁺and Eu³⁺ions coexisted inCdWO₄crystal and the energy transfer occurred between Eu²⁺and Eu³⁺ions. When the crystal wasexcited by266nm light, the energy corresponding to the4f65d to8S7/2transition of Eu²⁺ions resulted in the excitation of the Eu³⁺ions to the5DJlevel. The effect on the fluorescence fromannealing in oxygen at various temperatures was investigated. The excitation intensity of Eu²⁺ionat266nm decreased as annealing temperature increased from300to1073K due to the reductionof the oxygen vacancies, but remained at a certain equilibrium level when the annealingtemperature was further increased.