Structural, thermal, and luminescence kinetics of Sr4Nb2O9 phosphor doped with Dy3+ ions for cool w-LED applications

In this study, a series of white-light-emitting strontium niobium oxide {Sr4Nb2O9: xDy3+ (x = 0.01, 0.03, 0.05, 0.07, and 0.10 mol)} phosphors were synthesized via solid-state reaction approach and analyzed by using XRD, SEM, diffuse reflectance, photoluminescence (PL), and temperature-dependent PL (TDPL) spectroscopy. The cubic structure of Sr4Nb2O9 microparticles was identified by inspecting the diffraction pattern of the freshly generated phosphor. The formation of heterogeneous microstructures, including some aggregation, was seen in the SEM image of Sr4Nb2O9 phosphor. Diffuse reflectance and PL were examined for varying dopant ions concentration to explore the optical luminescence characteristics of Sr4Nb2O9 phosphor materials. Further, absorption spectra were obtained by using the diffuse reflectance spectra. The PL spectra of as-prepared phosphor exhibit two peaks at 483 nm and 580 nm, corresponding to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions, respectively. By correlating absorption and PL spectra, Judd oflet parameters were evaluated. The intensity of PL spectra of as-prepared phosphors increases up to 7 mol% and beyond that, it decreases. It is also affirmed that the PL intensity is maximum for the 7 mol% Dy3+ ions-doped Sr4Nb2O9 sample. The PL lifetime of the level 4F9/2 was evaluated by exciting the Dy3+ ions at 350 nm. By applying the Inokuti-Hirayama model to decay curves, the energy transfer process was explored. The CIE chromaticity coordinates of all the as-prepared phosphors lie in the white zone of the chromaticity diagram. The PL intensity remains 71% at 200 °C that of at room temperature, indicating the phosphor's exceptional thermal stability. From the aforesaid findings, it is observed that Sr4Nb2O9: Dy3+ phosphor is a promising choice for lighting and luminescent devices.