Upconversion luminescence of Er³⁺/Yb³⁺ doped Sr₅(PO₄)₃OH phosphor powders

Sr₅(PO₄)₃OH co-doped with Er³⁺and Yb³⁺ powder phosphors were synthesized by urea combustion method. The crystal structure was analyzed using X-ray diffraction (XRD). Particle morphology was analyzed using a Jeol JSM 7800F thermal field emission scanning electron microscope (FE-SEM) and the chemical composition analysis was carried out using an Oxford Instruments AzTEC energy dispersive spectrometer (EDS) attached to the FE-SEM. Upconversion emission was measured by using a FLS980 Spectrometer equipped with a 980 nm NIR laser as the excitation source, and a photomultiplier (PMT) detector. The XRD data of the Sr₅(PO₄)₃OH powder exhibited characteristic diffraction patterns of the hexagonal structure referenced in the standard JCPDS card number 00-033-1348. The sharp peaks revealed the formation of crystalline Sr₅(PO₄)₃OH. The powders were made up of hexagonal nanospheres. The enhanced red emission due to the ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺ was observed and was attributed to up conversion (UC) energy transfer from Yb³⁺. The upconversion energy transfer mechanism from Yb³⁺ to Er³⁺ is discussed.