Strontium Phosphate Composite Designed to Red-Emission at Different Temperatures

Eu³⁺-doped Sr₁₀(PO₄)₆(OH)₂-Sr₃(PO₄)₂ (SrHAp-TSP) composites were obtained via the microwave-stimulated hydrothermal method and post-heat-treated from 750 to 950 °C. Concentration of the Eu³⁺ ions was set to be 0.5, 1, 2, 3, 5 mol% in a ratio of the strontium ions molar content. The structural and morphological properties were investigated by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FT-IR) techniques. The average particle size of the studied materials annealed at 750, 850 and 950 °C were counted about 100, 131 and 173 nm, respectively. The luminescence properties depending on the dopant ion concentration, heat-treatment temperature, excitation wavelength and temperature were investigated. In the emission spectra, a broad peak corresponding to the 4f⁶5d¹ → 4f⁷ (⁸S_7/2) emission of Eu²⁺ ions as well as narrow 4f-4f transitions typical for Eu³⁺ ions can be observed. The luminescence intensity of the 1 mol% Eu³⁺:Sr₁₀(PO₄)₆(OH)₂-Sr₃(PO₄)₂ was measured depending on the ambient temperature in the range of 80-550 K. The CIE 1931 (International Commission on Illumination) chromaticity diagram was determined from emission spectra measured in 80, 300 and 550 K. The reduction mechanism of the Eu³⁺ to the Eu²⁺ was explained by the charge compensation mechanism based on the Kröger-Vink-notation. The decay times were measured and the Judd-Ofelt (J-O) theory was applied to analyze the observed structural and spectroscopic features.