Effect of Cr3+ and alkaline-earth metal ions co-doping on the enhancement of upconversion luminescence in β-NaYF4:Yb3+/Er3+ microparticles

To investigate the optical properties of rare earth upconversion particle, the Cr 3+ and alkaline-earth ions (Mg 2+ or Ca 2+ ) co-doped β-NaYF 4 :Yb 3+ /Er 3+ upconversion microparticles (UCMPs) were synthesized via a facile hydrothermal method . The influences of co-doping ions and their concentrations on crystal structure, particle morphology and optical properties were thoroughly investigated by XRD , SEM , FT-IR spectra, UV–VIS-NIR absorption spectra and photoluminescence spectra. And the effects of the two kinds of impurity ions co-doping on the UC particle growth were studied. We found that luminescence quenching could be inhibited by using Cr 3+ and Mg 2+ co-doping due to the asymmetrical ion arrangement around activator. However, the Cr 3+ and Ca 2+ co-doping was found to quench the upconversion luminescence (UCL), and the possible mechanism was suggested. These discoveries lead to new insights into the quenching effect and new strategy to design UCMPs for better luminescence performance.