Optical characteristics and Judd-Ofelt analysis of novel Ba3Sr(1-x)Nb2O9: xEu3+ phosphors for luminescent applications

Abstract

Phosphor converted white light emitting diodes (pc-WLEDs) offer a highly promising solution for the development of efficient and sustainable solid state lighting technologies. In this work, UV/NUV/blue LED excitable red emitting triply perovskite type Ba₃Sr_(1-x)Nb₂O₉: xEu³⁺ (x = 0.02,0.04,0.06,0.08,0.10, and 0.12) phosphors were prepared using the conventional high temperature solid state reaction method. Structural and morphological studies were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS), and fourier transform infrared spectroscopy (FTIR). XRD analysis confirmed the formation of a hexagonal structure with high purity, and the successful incorporation of Eu³⁺ ions was demonstrated. FESEM and TEM analysis revealed an agglomerated block like morphology. The calculated d-spacing values from HRTEM were consistent with the XRD results. EDS confirmed the elemental composition of the prepared sample. The optical properties were studied using diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) spectroscopy. From DRS and PLE spectra confirmed that the prepared phosphors could be efficiently excited at 280, 393, and 466 nm, corresponding to the dominant emission wavelengths of UV, NUV, and blue LED chips. Under these excitations, the characteristic peaks of Eu³⁺ ions corresponds to ⁵D₀ to ⁷F_J (J = 1,2,3 and 4) transitions were observed, in which most intense emission recorded at 609 nm. The optimum Eu³⁺ concentration was found to be x = 0.08 based on the concentration dependant PL spectra and the concentration quenching mechanism was ascribed to dipole-dipole interactions. PL emission decay curves show a double exponential nature, with shorter lifetimes in the millisecond range. The PL emission studies exhibited the generation of orange red light with CIE color coordinates (0.61,0.38), (0.62,0.37) and (0.63,0.36), achieving color purity of 100 % in warm light region. The internal quantum efficiency was determined to be 31.38 % under 393 nm exciation and 35.9 % under 466 nm exciation. JO theory was used to calculate the spectroscopic parameters (Ω₂ and Ω₄) with the trend following Ω₂ > Ω₄ and the radiative parameters such as branching ratio, total transition probability, stimulated cross-section were evaluated. The better stimulated crossection and excellent orange red emission properties suggest the potential of Eu³⁺ doped Ba₃SrNb₂O₉ phosphors are a promising candidate for red emitting lasers and next generation solid state lighting applications.