Investigation of luminescence properties and ratiometric thermometry through yellow-to-blue Dy3+ emission in Ca3La7(SiO4)5(PO4)O2 apatite

Identifier:  imarina:9462749

Handle: https://hdl.handle.net/20.500.11797/imarina9462749

Authors:  Douzi, Abir; Slimi, Sami; Madirov, Eduard; Serres, Josep Maria; Sole, Rosa Maria; Ben Salem, Ezzedine; Turshatov, Andrey; Richards, Bryce S; Mateos, Xavier

Abstract:
Dy3+-doped Ca3La7(SiO4)5(PO4)O2 (CLSPO) phosphors were synthesized via a solid-state reaction method and characterized for their structural, optical, and thermometric properties. X-ray diffraction (XRD) and Rietveld refinement confirmed a hexagonal apatite-type structure (P63/m) with refined lattice parameters of a = b = 9.604(3) & Aring;, c = 7.103(1) & Aring;. First-principles calculations for the undoped crystal revealed a direct bandgap of 4.08 eV, confirming CLSPO as a suitable host material for luminescent applications. Photoluminescence spectra exhibited characteristic Dy3+ emissions, with two blue bands (B1: 468 nm, B2: 479 nm) and two yellow bands (Y1: 543 nm, Y2: 575 nm). The yellow-to-blue (Y/B) intensity ratio displayed a strong temperature dependence, establishing CLSPO:Dy3+ as a promising candidate for luminescence-based thermometry. The optimal Dy3+ doping concentration was determined to be 3 at%, beyond which concentration quenching effects were observed. Photoluminescence studies further demonstrated that electric dipole-dipole interactions govern the dominant energy transfer mechanism, as evidenced by concentration-dependent quenching behavior. The absolute photoluminescence quantum yield (PLQY) was 5.7%, and Arrhenius analysis determined an activation energy of 0.11 eV. The decay time decreases with increasing Dy3+ concentration (from 658 mu s at 0.5 at% Dy3+ to 252 mu s at 10 at%). The fluorescence intensity ratio (FIR) method for optical thermometry revealed an absolute sensitivity (Sa) of 3.27 10-4 K-1 at 298 K, while the repeatability (R) of the Y/B ratio exhibited a reproducibility of 95.88% at 298 K, ensuring consistent and reliable temperature sensing performance. Furthermore, the luminescence remained stable over three hours of multiple heating-cooling cycles (298-523 K), confirming excellent photostability and reversibility. These results establish CLSPO:Dy3+ phosphors as highly efficient, thermally stable, and optically robust materials for next-generation temperature sensors, solid-state lighting, and advanced photonic applications.