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Revealing the cluster-structure-dependent red-to-green ratio transformation in Er:CaF2 crystals
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The evolution of Er3+ clusters in CaF2 crystals has not been fully understood, making the underlying mechanism for regulating the upconversion luminescence color of Er:CaF2 crystals remains unclear. In this work, the first-principles calculation is combined with the synchrotron X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), as well as the dielectric spectra and absorption spectra to study the Er-doped CaF2 crystals. The spectral analysis reveals the potential mechanism underlying the red-to-green (R/G) ratio transformation; specifically, the cross-relaxation rates of different clusters differed significantly. Based on this result, a strategy of cluster-controlled Er3+ R/G ratio has been proposed and verified by Er3+ and Y3+ co-doped CaF2 crystals. Our findings provide valuable insights for further design and precise control of Er3+ ion luminescence.
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