Study On Temperature Property And Luminescence Increasement Of Li⁺ And Rare Earth Ions Co-doped ZrO₂ Nanocrystalline Powders

Up-conversion luminescence nano-materials of doping rare earth irons have been applied in many fields such as short wavelength lasers, color displays, high density optical data reading and storage, biological fluorescent labels, phosphors, submarine communications etc. There were lots of reports about the up-conversion luminescence nano-materials of doping rare earth irons, among these reports, a careful choice of the host matrix, rare earth irons doping concentration and excitation pathways were critical on enhancing luminescence quantum efficiency. However, the up-conversion luminescence efficiency has been low; improving the up-conversion luminescence intensity is an important research direction. Recently, our group found that the up conversion luminescence intensity of ZrO₂ nano-powders is enhanced greatly by inducing Li⁺ and rare earth ions.In this paper, Erbium and ytterbium co-doped ZrO₂ nanocrystals with and without Li⁺ ions were synthesized by the Sol-gel method at the different sintering temperature. We found that the structure of the sample with Li⁺ ions is the same as that of the sample without Li⁺ ions by XRD spectra. By choosing the ratio of doping Li⁺ and rare earth irons carefully, the nano-powders of excellent luminescence properties were obtained. Up-conversion photoluminescence spectra of the different sintering temperature's samples were studied with 980 nm diode laser at room temperature. The luminescence intensity of single green and red band was found to be both greatly enhanced by introducing different Li⁺ ions concentration. The dependence of the fluorescence intensity with excitation power was studied as well. We found that the green light comes from the contribution of the two-photon process under the excitation power in the region from 40mW to 3535mW. While the red light mainly derives from the two-photon process under the low excitation power, and the collective contribution of the energy transfer process and two-photon process to the red light under high excitation power. Furthermore, the energy transfer process plays the dominant role to the red light at high excitation power. The simplified energy level model was constructed, the mechanism of the luminescence was analyzed through the model, and the results were well explained.With the FIR theory for temperature measurement, the sensitivity of the sample (ZrO₂: 0.5mol%Er3+/5mol%Yb3+/2mol%Li⁺) was obtained successfully, the influence factor including different peak, different Li⁺ doped concentrations, different exciting power and different sintering temperature of the sample were discussed in details. Additionally, with the experimental data researched, the expression of the sensitivity was obtained. At last, we found that the sensitivity was maximum using fluorescence intensity ratio of 525 nm and 562 nm, and the doped Li+ irons only affected the luminescence intensity of the sample not affected the sensitivity of the sample. With the increasing of the excited power, the working temperature decreased correspondence to the maximal sensitivity; the sintering temperature of the sample also affected the sensitivity, the higher sintering temperature, the smaller sensitivity.