From BPS4 to AB3P2S10 (A = Na, K): cations inducing dimension reduction and bandgap enlargement

Abstract

Regulating the crystal structure by cations is one of the most effective methods to adjust the performances of optical materials and enrich the structural chemistry of solid-state inorganic crystals. In this work, only boron-thiophosphate BPS₄ (BPS) was used as the template. By introducing alkali metal ions, Na⁺ and K⁺, the synthesis, structural revolution, and bandgap adjustment were studied. Namely, the first quaternary boron-thiophosphates, AB₃P₂S₁₀ (A = Na, K) (ABPS) were obtained, whose anion skeleton decreased to zero dimension from one dimension (1D) in BPS. In addition, the bandgap showed obvious improvement from 3.30 (BPS) to 3.42 and 3.49 eV (ABPS). Structural studies and theoretical analyses indicated that the insert of cations separates the infinite chains to [B₃P₂S₁₀] clusters, localizes the electrons around the S²⁻ in [BS₄] and [PS₄] groups, and widens the bandgaps. This work could enrich the structural chemistry of boron-thiophosphates and reveal that ionic bonds can modulate the covalent skeleton and show the effect on the optical properties.