Electronic structure analysis, a large Stokes shift of Bi3+ in BiSr3(YO)3(BO3)4 and color-tunable emissions by energy transfer to Eu3+ dopants

Abstract

A series of BiSr₃(Y_1−xEu_xO)₃(BO₃)₄ (0 ≤ x ≤ 0.4) phosphors with color-tunable emissions were synthesized, and their photoluminescence properties were systematically investigated. Powder X-ray diffraction confirmed the phase purity and successful cationic substitution, as evidenced by the linear expansion of the unit cell parameters resulting from the replacement of Y³⁺ with larger Eu³⁺ ions. Density functional theory calculations indicate that the VBM of the host is mainly composed of non-bonding O 2p orbitals, and the CBM is primarily composed of anti-bonding orbitals resulting from the interaction of Bi sp_z hybrid orbitals and O 2p orbitals. Upon excitation at 244 nm, BiSr₃(YO)₃(BO₃)₄ (BSYB) exhibits a broad green emission, involving the Bi–Y metal–metal charge transfer transition. Notably, BSYB displays a large Stokes shift of 22 116 cm⁻¹, which is uncommon among Bi³⁺-phosphors. Once doped with Eu³⁺, the Bi³⁺ to Eu³⁺ energy transfer was confirmed by the decreased lifetime of Bi³⁺ emission, and this energy transfer occurs via electric dipole–dipole interactions. By increasing the Eu³⁺ content, the emission color changes from green to red, and the temperature-dependent photoluminescence emission spectrum of BSYB:0.05Eu³⁺ exhibits high thermal stability with a T₅₀ of 207 °C.