In this work, the up-conversion phosphor NaYF 4 :Yb 3+ , Er 3+ nanocrystalline mixed with P 25 and TiO 2 hollow microspheres with high light scattering ability were fabricated as electrode for dye-sensitized solar cells (DSSCs). Meanwhile, we take advantage of the low cost feature of the carbon counter electrode to replace the precious metal Platinum (Pt) of DSSCs. SEM results show that the well-dispersed TiO 2 hollow microspheres size is 1.5 μm with surface consisting of a large number of rice-like nanorods. The particle size of the as-prepared NaYF 4 :Yb 3+ , Er 3+ nanoparticles is about 80 nm. The Photocurrent-Voltage curve of P 25 /NaYF 4 :Yb 3+ , Er 3+ cell under 980 nm infrared light has an obvious infrared photoresponse. The fabricated DSSCs using NaYF 4 :Yb 3+ , Er 3+ achieves power conversion efficiency (PCE) of 5.27% under one sun illumination, which shows an increase of 16% when compared with the benchmark P 25 cell (4.55%). In addition, the optimized DSSC using TiO 2 hollow microspheres as the top scattering layers with NaYF 4 :Yb 3+ , Er 3+ /P 25 exhibits a prominent PCE of 6.23%, which shows a 37% increase in conversion efficiency when compared with the commercial P 25 cell (4.55%). The increase in conversion efficiency should be contributed to the dual effects of the enhanced light harvesting of up-conversion NaYF 4 :Yb 3+ , Er 3+ and light utilization of the top light scattering TiO 2 hollow microsphere.
A series of NaYF4:Yb3+/Tm3+@NaYF4:Yb3+/Er3+ nanoparticles doped with Tm3+ and Er3+ were successfully prepared by the solvothermal method. Under 980 nm laser excitation, intense upconversion emission peaks of Tm3+ and Er3+ were observed for all samples. By doping Tm3+ and Er3+ with core–shell partitioning, not only a significant increase in fluorescence intensity could be achieved, but also simultaneous temperature measurements on multiple thermocouple energy levels could be realised. In addition, the temperature sensing performance of different thermocouple energy levels was also investigated, and it was found that the 3F3 → 3H6 and 1G4 → 3F4 thermocouple energy level pairs of Tm3+ were the best, with maximum absolute sensitivity and maximum relative sensitivity of up to 0.0250 K−1 and 2.155% K−1 respectively, higher than the sensitivity of other thermocouple energy levels. It has a temperature resolution of less than 0.0139 K, which is lower than that of most materials available today. By using this material as a probe to build a fiber optic temperature sensor platform, it was found to have reliable temperature measurement performance.
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