Effects of trivalent rare-earth ions on spectral properties of PbWO4 crystals

The pure and trivalent rare-earth ions doped lead tungstate crystals have been grown using Czochralski method. Optical absorption measurements in the wavelength range of 200-800 nm have been carried out on the doped PbWO4 crystals. Trivalent rare-earth ions doping have a threshold effects on the optical absorption band gap of PbWO4 crystals. Compared to that of pure PbWO4, the optical absorption edge of La3+-doped samples at lower in low concentration (50 and 150 ppm), show the shift of to high energy region (short wavelength), while with increasing of La3+ doping, the optical absorption edge shift fast to low energy region (long wavelength). Raman spectra have been investigated in a series of lead tungstate crystals doped with La3+ ions. The data were compared with the results in undoped PbWO4 and a (Mo, F)-doped sample. The dependence of frequency shift on doping was employed to deduce and approve the doping mechanism of rare-earth ions in PbWO4 lattice. The effects of La3+ doping on the photoluminescence spectra were also investigated.