This method is grounded in the concept of UC luminescence, a procedure where low-energy photons (in the near-infrared, NIR spectrum) are transformed into high-energy photons (in the visible spectrum) through the anti-Stokes mechanism.Firstly, the Yb3+ ions absorb low energy photon with wavelength about 980 nm, then Yb3+ ions might effectively transfer energy to Ho3+ ions due to the energy levels matching in between Yb3+ ions and Ho3+ ions, while the Ho3+ ion accepts the energy from 2 different Yb3+ ions, it is able to give off one photon with wavelength of 550 or 650 nm, and the strength ratio of these 2 emission bands is called luminescence strength ratio (LIR). This method, the temperature can be deduced by specific LIR.Advancements in Optical ThermometryResearchers led by Prof. Shoujun Ding at Anhui University of Technology (AHUT), China, are interested in optical thermometry with single crystal, the standard LIR technique relies on detecting the thermally paired two energy levels such as Er3+ (2H11/2, 3S3/2) and Tm3+ (3F2,3, 3H4) which are limited by the energy gaps between these sets of levels, but in Ho3+ ions, the non-thermally combined energy levels (5F4/5S2 and 5F5) with energy space of 3000 cm– 1 allow greater sensitivity.The non-contact thermometry method based on LIR makes it possible for the realization of temperature level measurement in particular harsh conditions such as intracellular, coalmines and power stations. The single crystal Gd0.74 Y0.2 TaO4 is selected to hold Yb3+ ions and Ho3+ ions instead of traditional phosphors, this crystal owns low symmetry and strong crystal field, which is conducive to improving the photoluminescence performance of Re ions.
