Luminescence Properties And Temperature Sensing Behavior Of Rare Earth Doped AB₂O₄?A=Sr,Ba B=Lu,Sc? Upconversion Materials

The rare earth doped up-conversion material has become a research hotspot in the recent years,because of the absorbing low-energy pumped photons to radiate high-energy photons.Up-conversion luminescence has many advantages,such as good monochromatic emission,tunability of luminescence and reducing material degradation caused by photoionization.In the application,its temperature sensing characteristic has the advantages of non-contact temperature measurement,high accuracy and strong anti-electromagnetic interference ability.Therefore,it is significant to find out the up-conversion materials with good luminescence performance and explore its temperature sensing characteristic.SrLu₂O₄ and BaSc₂O₄ are few reported as matrices for up-conversion materials.Here,we do some research on Er³⁺,Yb³⁺,Ho³⁺,La³⁺and non-rare earth ion of Zn²⁺doped SrLu₂O₄ and BaSc₂O₄.They are investigated including lattice occupancy of the doped ions,luminescence influence,pump power dependence analysis,energy transfer mechanism of up-conversion,and temperature sensing characteristics.The introduction of La³⁺and Zn²⁺improved the luminescence intensity successfully and temperature sensing parameters of these two up-conversion materials are got.The main works are as follows:?1?SrLu₂O₄:Er³⁺/Yb³⁺were obtained.From the analysis of crystal structure and coordination environment,the rare earth ions could entered the host lattice and replace the Lu³⁺.The doping amount of Er³⁺and Yb³⁺would affect the fluorescence intensity,and the optimized concentration is x=0.05,y=0.4 for red emission and x=0.05 and y=0.15 for green emission.The pump power dependence suggests that the radiative transition is a two-photon process.Using the fluorescence intensity ratio technology,the temperature sensing function is FIR=4.53?exp?-1090.6/T?.The maximum absolute temperature sensitivity is 0.0022 K^-1 and the maximum relative sensitivity is 0.012 K^-1.?2?The incorporation of La³⁺improves the fluorescence intensity and temperature sensing of SrLu₂O₄:Er³⁺/Yb³⁺.The XRD characterization showed that the La³⁺ions caused the diffraction peaks along the?320?and?121?crystal plane to shift to a small angle,indicating that the introduced La³⁺occupied the Lu³⁺lattice position.The La³⁺ions enhanced the green and red emission intensity by 19 and 30 times,respectively.Also,the reason for the enhancement was that La³⁺adjusted the local crystal field symmetry to break the parity forbidden of 4f electric dipole internally for the rare earth ions.And the maximal absolute sensitivity is 0.0023 K^-1 at 553 K after La³⁺doping,higher than without La³⁺was doped.It indicates that La³⁺doping can improve the temperature sensing.?3?The pure phase of BaSc₂O₄:Er³⁺/Yb³⁺were obtained.The analysis of the crystal structure,coordination environment and substitution principle proved that rare earth ions occupy the lattice positions of Sc³⁺.The optimized doping concentration is x=0.07(Er³⁺),y=0.5(Yb³⁺).The pump power dependence proves that the material's radiative transition is a two-photon process.According to the fluorescence intensity ratio,the temperature sensing function is FIR=8.09?exp?-1050/T?.When the temperature is 513 K,the absolute sensitivity value reaches the maximum,which is 0.0042 K^-1.Also the maximal relative sensitivity is 0.011 K^-1 at 303 K.?4?Zn²⁺ions can improve the fluorescence intensity and temperature sensing of BaSc₂O₄:Er³⁺/Yb³⁺.The XRD pattern showed that the incorporation of Zn²⁺increased the doping concentration of Yb³⁺into the host lattice.The incorporation of Zn²⁺changed the local crystal phase.Zn²⁺occupied the lattice sites of Sc³⁺in the host.Optimizing the doping concentration?y=0.08?of Zn²⁺increase the green and red emission intensity by 4and 10 times,respectively.There are three reasons for improving the emission intensity:?a?increasing the Yb³⁺'s concentration;?b?changing the local crystal phase;?c?the incorporation of Zn²⁺adjusts the local crystal field around the luminescence centers and reduces the crystal field symmetry.The introduction of Zn²⁺improves the absolute sensitivity by 0.0003 K^-1.?5?For BaSc₂O₄:Ho³⁺/Yb³⁺materials,the optimized doping concentrations of Ho³⁺and Yb³⁺were x=0.02 and y=0.5.The overall emission of the sample is green.Its radiative transition is a two-photon process.Using fluorescence intensity ratio technology based on the non-thermal coupling levels,the temperature sensing function is FIR=16.7-0.08T+(1.37?10^-4)T²-(8.27?10^-8)T³ and its maximum absolute sensitivity is-0.0198 K^-1.