High Light Yield of Sr₈(Si₄O₁₂)Cl₈:Eu²⁺ under X‑ray Excitation and Its Temperature-Dependent Luminescence Characteristics

In this work, we first investigate the relationship between temperature and lattice parameters by means of Rietveld refinement and then demonstrate its impact on the luminescence peak position of Eu²⁺ in Sr₈(Si₄O₁₂)­Cl₈. It is found that with increases in temperature, lattice expansion takes place without significant distortion of the coordination around Eu²⁺. As a result, the crystal field splitting of the Eu²⁺ 5d state decreases. At the same time, with the experimental data of the full width at half-maximum of Eu²⁺ emission at different temperatures and the infrared spectrum, the effective phonon frequency is evaluated and the main vibration motions are determined using first-principles calculation. Due to the high light yield under X-ray excitation and the excellent thermal stability of luminescence intensity and decay, a further optimized sample Sr_7.7Eu_0.3(Si₄O₁₂)­Cl₈ could be a potential scintillation material