Red-emitting Eu3+ activated LaSr2AlO5 phosphor for wLEDs: Crystal structure, photoluminescence, thermal stability, Judd-Ofelt calculation and band-gap analyses

Red-emitting La1-xSr2AlO5:xEu3+ (x = 0.01-0.06) phosphors have been synthesized via gel combustion (GC) approach and their structure and luminescent characteristics were analyzed in detail. The tetragonal crystal structure (I4/mcm space group) of all generated La1-xSr2AlO5:xEu3+ (x = 0.01-0.06) phosphors have been established by X-ray diffraction and rietveld analysis. The shape and size of the phosphor has been examined using transmission electron microscopy (TEM) and the estimated crystallite size was found to be 32-65 nm. Energy Dispersive X-ray (EDX) analysis confirmed the chemical composition of the synthesized materials. The diffuse reflectance spectra (DRS) were used to compute the band gap energies (Eg) of the samples which emerged to be in region of 5.373-6.009 eV. The Eu3+ activated LaSr2AlO5 phosphors produce red emissions at 579, 592, 614, 656 and 708 nm, when excited at 395 nm. These emission bands are caused by 5D0 -> 7FJ (J = 0, 1, 2, 3, 4) electronic transitions of Eu3+ ion. The Judd-Ofelt theory further supports the performance of LaSr2AlO5:Eu3+ phosphors as a red emitting substance with high branching ratio corresponding to 5D0 -> 7F2 transition from Eu3+ center present in the low symmetry site. Computed chromaticity coordinates (x, y) indicate a high degree of color purity in the phosphors, providing additional evidence for the presence of red emission. Temperature dependent emission (PL) spectra revealed good thermal stability of the synthesized nanophosphors with activation energy (Ea) of 0.1384 eV.