New structural effects in SrMoO4:Tm³⁺/Ho³⁺ crystals

Rare-earth doping of strontium molybdate, SrMoO4, allows the combination of laser generation of light and its SRS conversion. The RE3+ introduction into the Sr2+Mo6+O4 matrix must inevitably lead to the appearance of point defects that will affect the possibility of the effective use of the material. In this work, we report comprehensive structural research of SrMoO4 single crystals both nominally pure and doped with different Tm3+ and Ho3+ concentrations, undertaken for the first time, using X-ray single crystal and powder diffraction (crystal structure), EXAFS/XANES (local structure), and optical spectroscopy. The compositions of the grown crystals are established for the first time. Introduction of RE3+ ions in the form of RE3+Nb5+O4 leads to partial substitution of Mo6+ ions by Nb5+ along with the main location of Nb5+ ions in the interstitial sites near the defect Mo6+ sites with the formation of their own distorted tetrahedra. Dopant ions either replace partially the Sr2+ ions (Ho3+ ions) or are located in the interstitial sites near the defect Sr2+ sites (Tm3+ ions). The effective distribution coefficients of the dopants are determined.