Gorobets I. Dielectric, optic parameters and point defects in lasing molybdate and tungstate single crystals doped by neodymium ions

The work is devoted to determination of affection of dopant composition on formation of compensating charge defects and properties of PbMoO4:Nd3+ and PbWO4:Nd3+ laser single crystals. Types and concentrations of point defects are determined in PbMoO4:Nd3+ and PbWO4:Nd3+ single crystals in depending on activator composition and Nd concentration by means of X-ray diffraction, dielectric and optic spectroscopy. Taking into account a mechanism of charge compensation, the models of activator centers are proposed. It was established, that in the grown by Czochralski method PbMoO4:Nd3+ single crystals: Nd3+ ions occupied the Pb crystallographic site, oxygen vacancies were not determined; the concentrations of molybdenum vacancies were determined for the crystals grown from PbMoO4-Nd2O3, PbMoO4-Nd2(MoO4)3, PbMoO4-NaNd(MoO4)2 melts; molybdenum vacancies were not determined for the crystal grown from PbMoO4-NdNbO4 melt; local surrounding of Nd in the crystal lattice depends on composition of Nd2O3, NdNbO4, Nd2(MoO4)3, NaNd(MoO4)2 dopants. The PbMoO4:Nd3+ crystal growth from PbMoO4-Nd2O3 and PbMoO4-NdNbO4 melts leads to one type activator center formation, from PbMoO4-Nd2(MoO4)3 and PbMoO4-NaNd(MoO4)2 – more than one. For PbWO4:Nd3+, crystal grown from PbWO4-Nd2(WO4)3 melt the transformation of activator center was determined under the change of Nd concentration from 0.48 to 0.55 аt.%. PbMoO4:Nd3+ crystals doped by Nd2O3 contain one type of activator center and demonstrate the highest value of damage threshold of 90 J/cm2. Damage threshold of the crystals containing two and more activator center and co-dopants lays in the interval of 25-60 J/cm2 (NdNbO4, Nd2(MoO4)3, NaNd(MoO4)2 dopants). On the base of determined activator center models in depending on Nd concentration and dopant composition, optimum dopant compositions and crystal growth conditions for production of improved SRS laser elements were chosen.