Local symmetry engineering and Judd–Ofelt decoupling in SrLaInO4:Eu3+ for high-purity red emission toward advanced solid-state lighting

Abstract

A highly efficient red phosphor, SrLaInO₄:Eu³⁺ (SLIO:Eu³⁺), was synthesized via a high-temperature solid-solution route for applications in near-ultraviolet (NUV) excited warm white light-emitting diodes (w-LEDs). Rietveld refinement verified that SLIO crystallizes in an orthorhombic Pca2₁ structure, where Eu³⁺ preferentially accommodates the low-symmetry La³⁺ site with a nine-coordinated [EuO₉] environment, effectively promoting the electric-dipole governed ⁵D₀ → ⁷F₂ transition. Upon 395 nm excitation, the optimized composition (x = 0.20, in mol) delivers intense red emission centered at 615 nm, exhibiting a high color purity of 95%. The optimized phosphor had (0.659, 0.340) Commission Internationale de l'Eclairage chromaticity coordinates, approaching the National Television System Committee red standard. Concentration quenching is governed by a dipole–dipole interaction mechanism, with a calculated critical energy transfer distance of 12.89 Å. Judd–Ofelt spectral analysis yields a notably enhanced Ω₂ value, suggesting increased local structural asymmetry and a stronger covalent character around Eu³⁺. The phosphor also featured a moderate luminescence decay time of 752 μs and a reduced optical band gap from 4.21 to 3.74 eV after Eu³⁺ incorporation with 2 mol. A warm w-LED fabricated using an NUV chip combined with SLIO:0.2Eu³⁺ and commercial blue/green phosphors achieved a correlated color temperature below 3100 K, demonstrating its strong promise as a high-performance red component for next-generation solid-state lighting based on phosphor-converted w-LEDs.