Crystal chemistry and optical analysis of a novel perovskite type SrLa2Al2O7:Sm3+ nanophosphor for white LEDs

Abstract Perovskite orange-red SrLa2(1-x)Al2O7:2xSm3+ (x = 0.01–0.07) nanocrystalline phosphor series were successfully synthesized by means of solution combustion route for the first time. X-ray diffraction (XRD) measurements were performed to analyze the structural framework and it was concluded that the resulted nanophosphors were well-crystallized in tetragonal lattice with the space group I4/mmm (139). The lattice constants and refinement factors for SrLa2Al2O7 and SrLa1.92Sm0.08Al2O7 compositions were obtained by performing Rietveld refinement technique. From transmission electron micrographs, the spherical or semi-spherical nature of highly agglomerated particles (20–30 nm range) was noticed. Further, the diffuse reflectance (DR) studies yielded the band-gaps for SrLa2Al2O7 (5.03 eV) and SrLa1.92Sm0.08Al2O7 (4.88 eV) powder samples. The photoluminescence investigation of nanophosphors revealed the strong orange-red luminescence at 600 nm (most prominent) attributed to 4G5/2 → 6H7/2 emission of Sm3+ ions under near-ultraviolet (NUV) excitation (λex = 407 nm). The optimum composition of Sm3+ in SrLa2Al2O7 lattice was found to be 4 mol%. However, the double exponential decay behaviour confirmed the simultaneous occupancy of two crystallographic sites by activator ions in the host matrix. In addition, the critical distance for non-radiative energy migration amid adjacent activator centres was calculated to be 15.07 A, using Blasse's relation. A detailed analysis of non-radiative relaxation rates (131.9531 s−1), radiative life time (1.79 ms) and quantum efficiencies (81%) was carried out using Auzel's modal. Finally, the results highlight the importance of SrLa2Al2O7:Sm3+ orange-red nanophosphors in white LEDs under NUV excitation.