Studies On Growth And Spectral Properties Of Doped ZnWO₄ Laser Crystals

Laser crystal materials are more and more used in military affairs, industry, medical treatment and scientific research, and so on. With the development of scientific techonology, higher qualities of laser crystals, such as broad absorption line and long fluorescence lifetime, are required. High quality ZnWO₄ crystals are easily grown, and properly studied as laser host crystals because of good chemical stability and radiation resistance.In this paper, the suitable temperature field, growth rate and rotation rate of the crystals were decided by a mount of experiments and theory analysis. A series of doped ZnWO₄ laser crystals were grown by Czochralski method, containing series of Eu:ZnWO₄, Nd:ZnWO₄ and Tm:ZnWO₄ laser crystals. And then, all the crystals were oriented, cut and polished into samples.The crystal structures of doped ZnWO₄ crystals were characterized. According to the results of X-ray diffraction spectrum, crystal structures of doped ZnWO₄ crystals didn't change. The defection system of {2[RZn]+―[VZn]2-} formed by doping Ce³⁺, Nd³⁺ and Eu³⁺ into crystal lattices, in which Ce³⁺, Nd³⁺ and Eu³⁺ ions can replace the Zn2+ and vacant defects of Zn2+ can keep the balance of charge.According to the absorption spectrum of Ce:ZnWO₄, we can draw the conclusion that the absorption peak, which is correlative with the transitions of 5d→4f of Ce³⁺, was strong and broad, and the absorption cross section is large. For example, the absorption cross section of Ce:Eu:ZnWO₄ can achieve 1.34×10-18cm2. So Ce³⁺ ions can absorb pump power effectively, which meat requirement of sensitive ions.The Judd-Oflet theory was described detailed. According by Judd-Oflet theory and absorption spectrum measurement results of Nd:ZnWO₄, the intensity parameters of Nd³⁺ ions in Nd:ZnWO₄ crystal were calculated to be ?2=6.8202×10-20cm2, ?4=0.4633×10-20cm2 and ?6=0.4435×10-20cm2, which are very important for calculating other spectral properties of Nd³⁺.The sensitive action of Ce³⁺ on Nd³⁺ and Eu³⁺ were studied by fluroresence spectrum. The energy transfer existing between Ce³⁺ ions and Nd³⁺ ions as well as Eu³⁺ ions obviously, enhance the intensities of the up-conversion fluorescence (locate at 474nm and 572 nm) of Nd³⁺ ions and the fluorescence (locate at 613nm) of Eu³⁺ ions. The sensitization mechanism and the energy transfer processes are presented. But we found that the sensitilization in Ce:Nd:ZnWO₄ was more obvious than in Ce:Eu:ZnWO₄, and the possible reason is that the energy transfer efficiency existing between Ce³⁺ ions and Eu³⁺ ions is low because of the large energy level difference between 5d of Ce³⁺ ions and 5D0 of Eu³⁺ ions.