Structural, thermal, and optical properties of Dy3+/K+ Co-Doped SmCa4O(BO3)3 phosphors synthesized by Sol-Gel method

Abstract

This study investigates the structural, thermal, and optical properties of Dy³⁺/K⁺ co-doped SmCa₄O(BO₃) ₃ (SmCOB) phosphors synthesized using a sol–gel method. X-ray diffraction (XRD) analysis confirmed the high crystallinity and phase purity of the SmCOB lattice. Rietveld refinement further detailed slight lattice parameter modifications induced by Dy³⁺ and K⁺ doping. Fourier-transform infrared (FTIR) spectroscopy identified characteristic vibrational modes of the SmCOB matrix, including symmetric and asymmetric B–O stretching vibrations. These modes remained largely unaltered after doping, indicating the structural stability of the host lattice. Photoluminescence (PL) studies excited at 369 nm identified Dy³⁺ emission peaks at 468 nm (blue), 574 nm (yellow), and a dominant 657 nm (⁴F_9/2 → ⁶H_11/2). Co-doping with K⁺ increased the PL intensity by 26 %, attributed to charge compensation, reducing non-radiative losses and optimizing the local crystal field around Dy³⁺ ions. Luminescence decay analysis revealed that the Dy³⁺-doped sample exhibited a longer lifetime component (456.6 μs) compared to the undoped sample. Furthermore, K⁺ co-doping led to a significant increase in the average lifetime (752.8 μs), suggesting a further reduction in non-radiative decay pathways. Temperature-dependent PL analysis demonstrated excellent thermal resistance, with a high activation energy ($E_a$ = 0.258 eV) for K⁺ co-doped samples, highlighting their suitability for high-power lighting applications. Chromaticity measurements positioned the phosphors in the cold white light region, demonstrating their potential for energy-efficient lighting and advanced display technologies.