Chemical bond parameters, bond energy and the local crystal sites of Eu3+ in Ca5(BO3)3F:1% Eu3+ phosphor

Abstract

The local crystal sites occupied by Eu³⁺ in Ca₅(BO₃)₃F:1% Eu³⁺ phosphor were investigated experimentally and theoretically. Ca₅(BO₃)₃F:1% Eu³⁺ was synthesized by high-temperature solid-state method in air. The crystal structure and optical properties of the phosphor were studied by X-ray powder diffraction and photoluminescence, respectively. Two different O²⁻ → Eu³⁺ CT broad bands with the peaks at 266 and 283 nm in Ca₅(BO₃)₃F:1% Eu³⁺ were detected, indicating the Eu³⁺ sites occupied Ca2 and Ca1, respectively. The different sharp f–f emission spectra under the excitation of 283 and 266 nm proved that there are two different local lattice environments around Eu³⁺ existing in Ca₅(BO₃)₃F:1% Eu³⁺. Environmental factor h_e, the standard deviation of environmental factor (EFSD) and the bond energy were used to illustrate and explain the site occupancy mechanism of Eu³⁺ into the host lattice. By comparing the intensity ratios of ⁵D₀ → ⁷F₂ transition to the ⁵D₀ → ⁷F₁ transition, I(⁵D₀/⁷F₂)/I(⁵D₀/⁷F₁) of Eu³⁺ at Ca2 (7.381) was found to be 2.5 times stronger than that of Eu³⁺ at Ca1 site (2.933). was calculated to analyze the I(⁵D₀/⁷F₂)/I(⁵D₀/⁷F₁) value. On the basis of the bond valence model, a bond-energy method was used to study the occupancy of the Eu ion, which indicated that the preferential sites of Eu ion occupancy in the Ca₅(BO₃)₃F are the Ca2 and Ca1 sites. All three theoretical calculation results are consistent with each other.