Influence of Ultrahigh Dilution Treatment of the Charge on the Growth and Spectroscopic Properties of Nd:MgMoO4 Potential Laser Crystal

Abstract

The influence of the charge treatment by ultrahigh dilution (UHD) technology on oxide single crystals grown by the Czochralski technique was studied for monoclinic MgMoO4 crystals doped by 1 at. % of Nd3+ ions. The series of 10 Nd:MgMoO4 crystals was grown from the charges that were subjected to UHD treatment, as well as from the charges treated with two types of control or with no special treatment at all. The grown crystals were studied by X-ray powder diffraction analysis, inductively coupled plasma atomic emission spectroscopy, mass-spectrometry, optical absorption, emission spectroscopy and luminescence kinetic analysis. We found that: (i) wetting of MgO + MoO3 mixture by a water-ethanol solution before calcining leads to some enrichment of the mixture with MoO3, whereas the wetting of the charge after the calcining leads to some enrichment of it with MgO; (ii) congruent melting composition of MgMoO4 crystal is in the field of some MoO3 excess; (iii) the solid-phase solubility of the excess MoO3 in MgMoO4 probably does not depend on temperature, whereas the solid-phase solubility of the excess MgO in MgMoO4 crystal depends on temperature. We suggest that the corresponding solidus line passes through the range of retrograde solubility; (iv) the crystals grown within this range are characterized by the enhanced Nd3+ segregation coefficient between the crystal and the melt (approximately 0.006 versus 0.004); (v) unit cell parameters of MgMoO4 crystal with the excess of MoO3 are larger than those of the crystal of the stoichiometric composition and of the crystal with the excess of MgO; (vi) the shapes of the optical absorption and luminescence spectra of Nd:MgMoO4 crystal do not depend on the charge treatment; (vii) luminescence decay kinetics are single-exponential for all the studied crystals, the luminescence decay time being different for the crystals grown from the charges that underwent different types of treatment; (viii) the luminescence intensity of Nd:MgMoO4 crystal grown from the charge that underwent UHD treatment before calcining (solid-phase synthesis) is reduced by an order of magnitude in comparison with the other studied crystals.