Upconversion photoluminescence of sub-micron lanthanum oxysulfide particles co-doped with Yb3+/Ho3+ and Yb3+/Tm3+ synthesized by optimized combustion technique

Upconversion sub-micron particles are one of the most perspective materials due to their wide application range, the most important being in the bio-medicinal field where they can be used for labeling, sensing, treatment or drug delivery. Chemically stable upconversion sub-micron particles of La2O2S co-doped with Yb3+/Ho3+ and Yb3+/Tm3+ were synthesized and characterized. Different concentrations of Yb3+/Ho3+ and Yb3+/Tm3+ were successfully incorporated into the hexagonal crystal structure of lanthanum oxysulfide using the optimized solution combustion synthesis method with urea as a fuel. Sub-micron particles of less than 50 nm in diameter showed the typical upconversion photoluminescence when exited by 980 nm laser. The highest PL intensities were obtained in La(2)O(2)5 co-doped with 8 wt% Yb and 1.5 wt% Ho, or in case of La2O2S:Yb3+/Tm3+ with 4 wt% Yb and 0.5 wt% Tm. The CIE 1976 chromaticity coordinates of Ho(3+ )photoluminescence emission are (0.119, 0.581), with color purity of 98.7 %. The chromaticity of upconversion emission was invariant to doping concentrations.