“…With a recent focus on photonic technologies, a great interest has arisen in noncentrosymmetric tetrahedral chalcogenide materials, which may have superior properties compared to well-known oxide analogues in the field of NLO. In the structures of BaRECuCh 3 , a tetrahedral structural motif is clearly visible, namely, one-dimensional [CuCh 3 ] 5– chains consisting of distorted tetrahedra connected by common vertices. ,− ,− The chains are separated from each other by rare earth and barium atoms . In addition, BaRECuCh 3 are semiconductors with a wide band gap , and can be used for deep-sea solar cells. , While sulfides BaRECuS 3 have been fully studied, ,,, the selenide derivatives are known only for RE = La, , Ce, Sm, Gd, Er, Sc and Y …”