The Study Of Thermal Effects And Sensing Characteristics Induced By Infrared Laser In The Rare-earth Upconversion Nanocrystal

Upconversion luminescence,converting near infrared light into visible emission,has been studied extensively for its potential applications in information processing,solid-state lasers,3-D display,fiber communications,temperature sensing,biological therapy,and so on.But unfortunately these applications are mostly restricted by the low efficiency of the upconversion processes.One effective method of improving upconversion efficiency is to increase incident light power.However,with the improvement of the incident light power,thermal effect produced by the incident laser and the heating effect of the sample surface or the surrounding environments will influence on the temperature measurement.This paper mainly studied the thermal effects and sensing characteristics induced by infrared laser in the rare-earth upconversion nanocrystals.First of all,we prepared Er³⁺:NaYF₄,Yb³⁺:NaYF₄ and Er³⁺/Yb³⁺:NaYF₄ nanacrystals with different concentrations in the research process.The powder samples were tested by X-ray diffractometer,which was used to analyze and confirm the samples'crystal phase.After tableting process,the samples'upconversion fluorescence spectrum were measured under different pump power by using the spectrum test system.We analyzed the variation of samples'integrated intensity?including green radiation band,red radiation band and total?and the integrated intensity ratio of red and green?R/G?under different ion doping concentration,and studied the samples'emission spectrum color through the CIE coordinate graphs.The samples'upconversion mechanisms were analyzed by means of energy level diagram,and we got the variation of intensity of peak wavelength with different ion doping concentration,and analyzed and studied the double logarithmic power relations.Secondly,the upconversion fluorescence spectrum of Er³⁺:NaYF₄ and Er³⁺/Yb³⁺:NaYF₄nanacrystals with different concentrations were measured under different temperatures.We analyzed the variation of samples'integrated intensity?green and red?under different temperatures.In addition,we studied the variation of the fluorescence intensity ratio?FIR?under different temperatures at the center wavelength?520 nm and 539 nm?,and drew the samples'graph of temperature sensitivity?S?under different temperatures by calculation.By comparing the maximum sensitivity and the corresponding temperature between different samples,we discussed the applications of temperature sensor of Er³⁺:NaYF₄ and Er³⁺/Yb³⁺:NaYF₄ nanacrystals according to the theory of FIR.Thirdly,the surface temperature distribution of rare earth doping O₂Y₃ ceramics was calculated by using COMSOL Multiphysics.Furthermore,we simulated the variation of peak temperature of sample's surface center under different laser powers,and got the change rule between peak temperature and laser power,and compared with experiment results.Then we studied the influence of thermal effect of infrared laser on the fluorescence process of rare eatth ion doping upconversion materials.We studied the influence of the surface temperature distribution of sample on FIR by using COMSOL Multiphysics under higher laser power,and got the revised FIR equation,and proposed the modified temperature sensing technology.On the basis of parameter calibration,we chose one sample to do experiments,and made comparison between the modified method and conventional method.The result indicates that the new-type temperature sensing technique has higher SNR.Finally,we found that FIR is not only related to ambient temperature,but also related to the laser power incident through the revised FIR equation,and proposed new-type laser power sensing technology.After measured the fluorescence spectrum of samples with different concentrations under different powers,we studied the variation of FIR at 520 nm and 539 nm under different powers,and calibrated the parameters.In the simulation experiments we considerd the influence of some factors on experiments including the size of laser spot,the wavelength of incident laser and varied materials,and found the technique has high accuracy,which independent on the complicated environments of materials,thus is suitable for applications in biological systems.