Crystal structure and photophysical features of greenish perovskite type SrLa₂Al₂O₇:Er³⁺ nanocrystals for down conversion white LEDs

Tetragonal phase perovskite type SrLa_2(1−x)Er_2xAl₂O₇ (x = 1.0–5.0 mol%) nanocrystals emitting green light were prepared by a facile, economical and efficient solution combustion route. Detailed analysis of their crystal structure and lattice refinement was carried out by x-ray Diffraction and Rietveld refinement, which confirmed their tetragonal phase along with 14/mmm (139) space group. Morphological investigation was done by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) which disclosed the spherical shape of nanoparticles with their average size in the range of 40-50 nm. Elemental composition of the nanophosphors was detected by Energy Dispersive x-ray Analysis (EDAX). Utilizing Diffused Reflectance Spectra (DRS), band gap value of the optimized sample i.e., SrLa_1.96Er_0.04Al₂O₇ was calculated as 5.01 eV. Photoluminescence studies indicated the green color emission of the synthesized nanophosphors with a prominent peak in the emission spectra at 548 nm due to ⁴S_3/2 → ⁴I_15/2 electric-dipole transition. Optimum concentration of the Er³⁺ was observed as 2.0 mol% above which concentration quenching process occurred via dipole-dipole non-radiative energy migration. Radiative lifetime value and quantum efficiency for optimized sample was determined as 0.546 ms and 68.33%, respectively. Moreover, color coordinates of the nanophosphors (0.2657, 0.6031) confirmed their emission in green region which enabled them to be a promising candidate in the phosphorescent sensors and tricolor (RedGreen-Blue) based white light emitting diodes (WLEDs). (paper)