Nanooptics and photonics
The influence of the impurities on the photoinduced effects in PbMoO4 and Pb2MoO5 single crystals
Bondar D.S., Bochkova T.M., Trubitsyn M.P., Volnyanskii M.D.
Laboratory of Active Dielectric Crystals, Dept. of experimental physics, Oles Honchar Dnipro National University, prosp. Gagarina 72, Dnipro, 49010, Ukraine 
E-mail: dima_bondar@ua.fm

	PbMoO4 and Pb2MoO5 crystals attract attention owing to outstanding acousto-optical properties. The disadvantages of both crystals are the yellow coloration of the as-grown crystals and the photochromic effect. There are many theories regarding intrinsic and photoinduced centers in PbMoO4. One of the most justified is the hypothesis about the formation of the Pb3+- (MoO4)3- nanoclusters as a result of UV irradiation exciting the luminescence in PbMoO4 [1].
In this work we analyze UV induced photochromic and photodielectric effects in doped PbMoO4 and Pb2MoO5 crystals. Earlier [2], we discussed photochromic effect in PbMoO4 as a result of recharging centers according to the scheme: Mo6+ + Pb2+  Mo5+ + Pb3+. The photodielectric effect causes the appearance of a relaxation maximum on the temperature dependence of the dielectric constant. We associate it with the arising of the dipole moment in anionic groups (MoO3)-, which are formed by capture of a photoelectron by molybdenum ions in tetrahedra distorted by the presence of an oxygen vacancy [3]. To clarify these hypotheses we studied the influence of the impurities replacing lead ions on some optical and electrical properties of PbMoO4 and Pb2MoO5 crystals.
PbMoO4 and Pb2MoO5 single crystals were grown by the Czochralski technique using high-purity raw materials and platinum crucibles. The crystals were doped with both elements with a stable electronic configuration (Ga3+, Bi3+, Mg2+, Ba2+) and elements of transition groups (Gd3+ and Cu2+). The grown single crystals were studied using methods of dielectric, optical, and EPR spectroscopy. The results are discussed in the framework of the presented models. 

1.	Van Loo W. Luminescence of Lead Molybdate and Lead Tungstate // Phys. Stat. sol. (a).-1975.-27.-P. 565-674.
2.	Bochkova T. M., Volnyanski M. D., Volnyanski D. M., Shchetinkin V. S. Color centers in lead molybdate crystals // Physics of the Solid State.-2003.-45.-P. 244–247.
3.	Bochkova T. M., Trubitsyn M. P., Volnyanskii M. D., Bondar D. S., Volnyanskii D. M.. Phenomena induced by UV irradiation in PbMoO4 single crystal // Journal: Molecular Crystals and Liquid Crystals.-2020 (in press).