Effect of the local environment on the luminescence of Er3+/Yb3+-doped aluminate upconversion phosphors

Abstract

In recent years, trivalent rare-earth ion (RE3+) doped upconversion luminescent (UCL) materials have been studied extensively owing to their potential applications. The structure of the material is the main factor affecting the UCL performance. In this study, three structurally identical Er3+/Yb3+ co-doped aluminates CaYAlO4, CaGdAlO4, and CaLaAlO4 (CYA, CGA, and CLA) phosphors were synthesized, and the effects of the local environment on the UCL performance of Er3+ ions were investigated. The morphology and phonon energy of the samples were not the main factors affecting the luminescence performance in the same structural material. The difference in the crystal field strength was the main reason for the difference in the UCL of the three phosphors, which was attributed mainly to the difference in the crystal field strength and the difference in the degree of distortion of the Al–O octahedra that changes the transition probabilities of the parity forbidden intra-4fN–4fN electronic transitions of Er3+. A comparison of the distances between the RE3+ and the lifetimes of the 4I11/2 and 4I13/2 energy levels in the three materials showed that the red–green ratio of the materials was affected by the energy transfer. Finally, an analysis of the changes in the energy band structure and density of states (DOS) distribution before and after Er3+/Yb3+ doping of CYA, CGA, and CLA found that the effect of the bandgap on the UCL can be neglected when the bandgap of the matrix is larger than the energy difference from the 4I15/2 energy level to the 2H11/2 energy level of the Er3+ ion.