Spectroscopic studies of strong red emitting Sr2SiO4:Eu3+ nanophosphors with high color purity for application in WLED using Judd-Ofelt theory and TL glow curve analysis

Un-doped and Eu3+ doped Sr2SiO4 nanophosphors were synthesized by self-propagating solution combustion synthesis and are characterised with different material and optical characterisations. X-ray diffraction (XRD) confirmed orthorhombic phase, transmission electron microscopy (TEM) revealed the nanophosphors with irregular shape but crystalline in nature. The photoluminescence (PL) excitation, emission spectra and lifetime are thoroughly discussed. The emission spectra due to the excitation under 393 nm showed better asymmetric ratios than the 260 nm excitation ensuring better color purity of 97%. The comparative investigations using commission international del'Eclirage (CIE) diagram also established that the color purity of 393 nm excitation is superior with CIE co-ordinates (0.66, 0.34) and is close to NTSC standards. The Judd Ofelt (JO) intensity parameters (Omega(2) and Omega(4)) were obtained from PL emission spectrum and the JO parameters followed the trend Omega(2) > Omega(4) for all Eu3+ concentration. Asymmetric ratios and JO analysis both indicated that the crystal field is non-centrosymmetric in nature. The radiative properties such as branching ratios, emission cross section, optical gain and gain bandwidth of optimised concentration are calculated. Photoluminescence lifetimes exhibited biexponential nature and showed higher lifetime for 393 nm excitation. Furthermore, the quenching due to non radiative energy transfer mechanism is dominated by multipole-multipole interaction. All these optical characterisations supported the fact that the nanophosphors excited at 393 nm have better pertinence towards display, laser and lighting application. Thermoluminescence (TL) studies of the nanophosphors were carried out. The kinetic parameters are calculated using general order kinetics and are verified by computerised glow curve de-convolution (CGCD). TL emission spectra and contour plots were analysed that further confirmed that the emission resembled the same as PL emission spectra.