[Upconversion luminescence properties of ZBLAN : Nd3+, Tm3+, Yb3+]

The ZBLAN : Nd3+, Tm3+, Yb3+ upconversion materials were prepared by high-temperature solid method. The concentrations of Tm3+ and Yb3+ were 0.01% and 0.3% respectively. The concentration of Nd3+ changed in the range from 0.1% to 2%. The absorption spectrum of ZBLAN : Nd3+, Tm3+, Yb3 in all samples from 300 to 1 000 nm was measured at room temperature. The upconversion emission was observed when excited by 798 nm infrared light. The material samples emitted relatively strong multi-band (the red, blue and green color) visible light. Based on the experiment, the multi-band visible spectral lines were analyzed, and the energy level transition mechanism was given. The blue light results from the transition of 1G4 --> 3 H6 of Tm3+, the green light is from the transition of 2 H7/2 --> 4 I9/2 of Nd3+, and the red light originates from the transition of 2 H11/2 --> I9/2 of Nd3+. The results show that the upconversion mechanism includes excited state absorption, energy transfer, cross relaxation and so on. The energy transfer processes between Nd3+, Tm3+ and Yb3+ ions both forward and backward prove to be the origin of upconversion emissions. The effect of rare earth doping concentration on the energy upconversion efficiency was analyzed, according to the different upconversion light emitting intensity from samples with different Tm3+ mol concentrations. The upconversion luminescence increased with the Nd3+ concentration and got its peak at 1.5%.