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

Perovskite orange-red SrLa2Al2O7:2xSm(3+) (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 14/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 (4)G(5/2) -> H-6(7/2) emission of Sm3+ ions under near-ultraviolet (NUV) excitation (lambda(ex) = 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 angstrom, 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.