Centrosymmetric to noncentrosymmetric structure transition of the RbREP2Se6 (RE = La–Nd, Sm, Ho–Yb) series: crystal growth, magnetic and optical properties

Abstract

Rare-earth (RE) chalcophosphates have attracted considerable attention as infrared nonlinear optical (NLO) materials. Herein, nine single crystals of quaternary rare-earth containing selenophosphates, RbREP₂Se₆ (RE = La–Nd, Sm, Ho–Yb) were synthesized using the RbI flux assisted boron chalcogen mixture (BCM) method. The compounds RbREP₂Se₆ (RE = La–Pr) crystallize in the monoclinic crystal system with the P2₁/c space group, whereas RbREP₂Se₆ (RE = Nd, Sm, Ho–Yb) crystallize in the orthorhombic crystal system with the P2₁2₁2₁ space group. In the RbREP₂Se₆ (RE = La–Pr) series, the structure is composed of [REP₂Se₆]⁻ layers formed by interconnected RESe₉ distorted capped square antiprism and P₂Se₆ dimers, while in the RbREP₂Se₆ (RE = Nd, Sm, Ho–Yb) series, [REP₂Se₆]⁻ layers consist of RESe₈ bicapped trigonal prisms and P₂Se₆ dimers. Polycrystalline powders of all the title compounds were also obtained for property measurements. Magnetic property measurements of RbREP₂Se₆ (RE = Nd, Er, and Yb), were collected over the 2–300 K temperature range, which revealed paramagnetic behavior with small negative Weiss constants. The bandgaps of RbREP₂Se₆ (RE = Nd, and Sm) were determined from UV-vis diffuse reflectance measurements. Second Harmonic Generation (SHG) measurements of RbREP₂Se₆ (RE = Nd, and Sm) polycrystalline samples exhibited an efficiency of ∼0.67 × AgGaS₂, and ∼3.65 × AgGaS₂ respectively.