Lattice distortion induced enhanced up-conversion luminescence from Er³⁺, Yb³⁺ codoped MgAl₂O₄ nanocrystals through...

Recently, rare earth activated nanomaterials have gained much attention due to their up-conversion emission-based lighting applications. In this research, we report on the significant increase in red/green emission intensity with Er³⁺, Yb³⁺, Cr³⁺ tridoping than Er³⁺, Yb³⁺ codoping in the MgAl₂O₄ nanocrystals. Four samples with different compositions Mg_0.94Er_0.01Yb_0.05Al₂O₄, Mg_0.9Er_0.05Yb_0.05Al₂O₄, Mg_0.89Er_0.01Yb_0.1Al₂O₄, and Mg_0.93Er_0.01Yb_0.05Cr_0.01Al₂O₄ were synthesized through the solution combustion method. Rietveld refinement confirmed a single-phase cubic spinel structure with the presence of lattice defects and octahedron distortion. Diffuse reflectance spectra showed broad absorption bands ascribed to host defects (such as oxygen vacancies and cation antisite defects), sharp emission peaks characteristic of Er³⁺ and Yb³⁺ ions, and broad absorption bands characteristic of Cr³⁺ ions. Codoped samples exhibited green and red emissions characteristic of Er³⁺, while 1 mol% Cr³⁺ incorporation led to enhanced red-green intensities and additional near-infrared emission from Cr³⁺ overlapping with Er³⁺ emission. This enhancement suggests the contribution of local lattice distortions in the tridoped sample toward strengthening the Yb³⁺ → Er³⁺ energy transfer. Consequently, the strong up-conversion photoluminescence exhibited by Er, Yb, and Cr tridoped MgAl₂O₄ nanocrystals highlights their potential for application in display technologies and solid-state lighting.