Investigation of optical properties of Ce³⁺-activated phosphors is not only of practical importance for various applications but also of fundamental importance for providing a basis to understand relevant properties of other lanthanide ions in the same host. We report herein a combined experimental and theoretical study of optical properties of Ce³⁺ in Li₄SrCa(SiO₄)₂. Photoluminescence properties of the material prepared by a solid-state reaction method are investigated with excitation energies in the vacuum-ultraviolet (VUV) to ultraviolet (UV) range at low temperatures. The band maxima in the excitation spectra are assigned with respect to 4f → 5d transitions of Ce³⁺ at the Sr and Ca sites, from comparison between experimental and ab initio predicted transition energies. As a result of the two-site occupation, the material displays luminescence at 300–500 nm with a high thermal quenching temperature (>500 K), consistent with the calculated large gaps (∼1.40 eV) between the emitting 5d levels and the bottom of the host conduction band. On the basis of experimental and calculated results for Ce³⁺ in Li₄SrCa(SiO₄)₂, the energy-level diagram for the 4f ground states and the lowest 5d states of all trivalent and divalent lanthanide ions at the Sr and Ca sites of the same host is constructed and discussed in association with experimental findings.

中文翻译：

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Ce掺杂的Li ₄ SrCa（SiO ₄）_2的光学性质：实验和理论相结合的研究

Ce ³⁺活化的磷光体的光学性质的研究不仅对于各种应用具有实际意义，而且对于提供基础以理解同一主体中其他镧系离子的相关性质也具有根本的重要性。我们在此报告了在Li ₄ SrCa（SiO ₄）₂中Ce ³⁺光学性质的组合实验和理论研究。通过固态反应方法制备的材料的光致发光特性在低温下在真空紫外（VUV）到紫外（UV）范围内的激发能下进行了研究。相对于Ce ^3+的4f→5d跃迁指定了激发光谱中的能带最大值通过比较实验和从头算预测的跃迁能，可以确定Sr和Ca的位置。由于存在两个位点，该材料在300-500 nm处显示出具有高的热淬灭温度（> 500 K）的发光，这与计算得出的5d发射能级与底部之间的大间隙（〜1.40 eV）一致主机导带 根据Li ₄ SrCa（SiO ₄）_2中Ce ³⁺的实验和计算结果，在Sr和Ca位置上所有三价和二价镧系离子的4f基态和最低5d状态的能级图结合实验结果构建和讨论了同一宿主的宿主。