Luminescence of Ce³⁺-Doped MB₂Si₂O₈ (M = Sr, Ba): A Deeper Insight into the Effects of Electronic Structure and Stokes Shift

A series of Sr_1-2xCe_xNa_xB₂Si₂O₈ and Ba_1-2xCe_xK_xB₂Si₂O₈ (x = 0.005, 0.01, 0.02, 0.04, 0.06, 0.08) samples were synthesized by a high-temperature solid-state reaction. The low temperature excitation, emission, and fluorescence decay spectra together demonstrated that all spectral bands arise from the Ce³⁺ ions located at only one kind of lattice site. The first-principles calculations of the structural and electronic properties of pure and Ce³⁺-doped MB₂Si₂O₈ (M = Sr, Ba) were performed, and the obtained results were used for understanding the structural changes after doping and identification of the observed position of the host absorption bands. The measured 4f-5d excitation and emission spectra of Ce³⁺ ions doped in MB₂Si₂O₈ were analyzed and simulated in the framework of the crystal-field (CF) theory. The electron-phonon coupling effect generally ignored in most studies published so far was also taken into account by applying the configurational coordinate model. The validity of such a combined insight into the 5d CF energy level positions and the Stokes shift has been confirmed by analyzing the dependence of the Ce³⁺ spectroscopic properties on the dopant concentration. In addition, the influence of temperature on the luminescent properties of the studied samples was also explored and is discussed.