Tunable emissions via the white region from Sr2Gd8(SiO4)6O2:RE3+ (RE3+: Dy3+, Tm3+, Eu3+) phosphors

Abstract

Single, double and triple trivalent rare-earth (RE³⁺ = Dy³⁺, Tm³⁺, Tm³⁺/Dy³⁺ and Tm³⁺/Dy³⁺/Eu³⁺) ions activated Sr₂Gd₈(SiO₄)₆O₂ (SGSO) phosphors were synthesized by a sol–gel process. X-ray diffraction profiles confirmed their oxyapatite structure after annealing at 1450 °C for 12 h. Morphological studies were performed by taking scanning and transmission electron microscopy images, which displayed rod-like shapes. SGSO phosphors exhibited good photoluminescence (PL) properties in the respective regions when doped with Dy³⁺ and Tm³⁺ ions. Dy³⁺ co-activated SGSO:Tm³⁺ phosphors revealed tunable emissions from cool white light to warm white light towards the yellow region based on the co-activator concentration. However, Eu³⁺ ions co-doped SGSO:Tm³⁺/Dy³⁺ phosphors tuned the emissions towards the red region. The energy transfers from Tm³⁺ to Dy³⁺ ions and Tm³⁺/Dy³⁺ to Eu³⁺ ions were established based on the energy level diagram. The cathodoluminescence properties of these phosphors showed excellent emission behavior when the single, double or triple trivalent RE ions were doped into the SGSO host lattice. Unlike the case of the PL, the energy transfer process was observed to take place. The calculated Commission Internationale de l'Eclairage chromaticity coordinates of Tm³⁺ and Dy³⁺ individual ion doped SGSO phosphors confirmed the blue and white emissions, while the co-doped samples exhibited tunable emissions.