Study On Growth And Spectrum Of ZnWO₄:Ho³⁺ Crystal

A series of different Ho3+ ion-doped and Ho3+,Yb3+ ion-doped concentrationsZnWO4 single crystals were grown with Czochralski method after carefully designingtemperature field and choosing technique parameters:?G≥30℃/cm,the rotation rateof 25~40r/m and pulling rate of 3~4mm/h. The concentrations of Ho3+ and Yb3+inZnWO4 single crystals were measured by ICP-AES method. The distributioncoefficients of Ho3+ and Yb3+ in ZnWO4 crystals were 0.26 and 0.372, respectively. Both energy level schemes of Ho3+ and Yb3+ in ZnWO4 crystal were confirmedafter the absorption spectra of ZnWO4: Ho and ZnWO4: Ho3+,Yb3+ had been observed..The absorption cross sections of Ho3+ at 488nm and 640nm were calculated to be1.2×10-21cm2 and 2.1×10-21cm2, respectively. The emission spectra of ZnWO4:Ho3+crystals were observed on 488nm and 514nm excitation. In ZnWO4: Ho3+, theupconversion spectrum around 550nm was observed upon being excited by 632.8nmlaser. The polarized emission spectra measurements of ZnWO4:Ho3+,Yb3+crystalpumped by 943nm were performed. The Judd-Ofelt theory was applied to calculate intensity parameters(?2=3.732×10-20cm2,?4=2.29×10-20cm2,?6=4.731×10-20cm2) of Ho3+ in ZnWO4crystal. The spontaneous emission transition rate, radiative lifetime, fluorescencebranching ratio and integrated emission cross section were obtained. Throughcarefully analysing the results, 5I7→5I8(2μm fluorescence ) was estimated as being themost effective transition which could cause laser emission.