Centrosymmetric to Noncentrosymmetric Structure Transition of the RbREP 2 Se 6 (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 P2 1 /c space group, whereas RbREP2S 6 (RE = Nd, Sm, Ho -Yb) crystallize in the orthorhombic crystal system with the P2 1 2 1 2 1 space group.In the RbREP2Se6 (RE = La -Pr) series, the structure is composed of [REP 2 Se 6 ] -layers formed by interconnected RESe 9 distorted capped square antiprism and P 2 Se 6 dimers, while in the RbREP2Se6 (RE = Nd, Sm, Ho -Yb) series, [REP2Se6 ] -layers consist of RESe 8 bicapped trigonal prisms and P 2 Se 6 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 x AgGaS 2 , and ~3.65 x AgGaS 2 respectively.