A green light emissive LaSr2AlO5:Er3+ nanocrystalline material for solid state lighting: crystal phase refinement and down-conversion photoluminescence with high thermal stability

Abstract

The present study reveals the structural and optoelectronic characteristics of a down-converted (DC) green luminous Er³⁺ doped LaSr₂AlO₅ phosphor that was produced by employing an efficient and reliable gel-combustion process assisted with urea as a fuel. Using Rietveld refinement of diffraction data, the crystal structure and phase formation were examined. The surface morphology and elemental configuration of the phosphor were analyzed via TEM and EDX spectroscopy, respectively. The band gap of LaSr₂AlO₅ (5.97 eV) and optimized La_0.96Sr₂AlO₅:4 mol% Er³⁺ (5.51 eV) classify the optimized sample as a direct band-gap material. The PL peaks located in the visible range corresponding to transitions ²H_9/2 → ⁴I_15/2 (406 nm), ²H_11/2 → ⁴I_15/2 (520 nm), ⁴S_3/2 → ⁴I_15/2 (550 nm), and ⁴F_{9/ 2} → ⁴I_15/2 (665 nm) were revealed by photoluminescence spectroscopy under 377 nm excitation. Above 4 mol% Er³⁺ doping, concentration quenching was observed, which was controlled by the quadrupole–quadrupole interaction. Based on the findings of the double exponential fitting of lifetime curves acquired from the emission spectra at λ_ex = 377 nm and λ_em = 550 nm, the average lifetime of the excited levels of considered nanomaterials was estimated. The temperature-dependent emission spectra of the La_0.96Sr₂AlO₅:4 mol% Er³⁺ sample were collected in the range 298–498 K. The considered phosphor was found to have a high thermal stability as evidenced by the luminous intensity being sustained at 74.29% at 498 K compared to the intensity at ambient temperature (298 K) with an activation energy of 0.1453 eV. The calculated color purity and superb chromaticity coordinates indicates that the phosphors have a high degree of color purity, which further supports its applicability as a green component in solid-state lighting.