Substitution priority of Eu²⁺ in multi-cation compound Sr_0.8Ca_0.2Al₂Si₂O₈ and energy transfer

A blue phosphor was obtained by doping Eu²⁺ into a multi-cation host Sr_0.8Ca_0.2Al₂Si₂O₈ through high temperature solid state reaction. The emission spectra show a continuous red-shift behavior from 413 nm to 435 nm with Eu²⁺ concentration increasing. The substitution priority of Eu²⁺ in Sr_0.8Ca_0.2Al₂Si₂O₈ was investigated via x-ray diffraction (XRD) and temperature properties in detail: the Ca²⁺ ions are preferentially substituted by Eu²⁺at lower doping, and with the Eu²⁺ concentration increasing, the probability of substitution for Sr²⁺ is greater than that of replacing Ca²⁺. Accordingly, we propose the underlying method of thermal property to determine the substitution of Eu²⁺ in the multi-cation hosts. Moreover, the abnormal increase of emission intensity with increasing temperature was studied by the thermoluminescence spectra. The energy transfer mechanism between the Eu²⁺ ions occupying different cation sites was studied by the lifetime decay curves. A series of warm white light emitting diodes were successfully fabricated using the blue phosphors Sr_0.8Ca_0.2Al₂Si₂O₈: Eu²⁺ with commercial red phosphor (Ca Sr)SiAlN₃: Eu²⁺ and green phosphor (Y Lu)₃Al₅O₁₂: Ce³⁺, and the luminescent efficiency can reach 45 lm/W. (paper)