Upconversion luminescence enhancement in NaYF4: Yb3+, Er3+ nanoparticles induced by Cd2+ tridoping

A series of Cd 2+ doped hexagonal-phase NaYF 4 : Yb 3+ , Er 3+ upconversion nanoparticles (UCNPs) were synthesized via solvothermal method, and the effect of Cd 2+ on the upconversion luminescence (UCL) properties was investigated in detail. It was found that the introduction of Cd 2+ could enhance the UCL intensities of NaYF 4 : Yb 3+ , Er 3+ UCNPs significantly. The maximum enhancement occurred when the doping concentration of Cd 2+ was 7   mol%. Compared with the UCNPs without Cd 2+ doping, the total integral emission intensity was enhanced by ∼38 times. It was related to the unit cell expansion and the generated F − vacancies, which could decrease the crystal symmetry around the Er 3+ ions. The results shall facilitate the improvement of UCL properties and the potential applications of UCNPs in lighting, solar cells, optics encoding and so on.