Fluorescence And Temperature Sensing Properties Of Ho³⁺doped NaYF₄ Nanoparticles

In this paper,the luminescence properties of Ho³⁺doped Na YF₄ nanoparticles(NPs)and their temperature sensing properties are investigated.The influence of Ho³⁺doping concentration on the emission intensities is studied and the concentration quenching mechanism of this material is analyzed.Fluorescence intensity ratios(FIR)of multi-emissions are used for investigating the temperature sensing performance of Na YF₄:3%Ho³⁺NPs in both visible(VIS)and near-infrared(NIR)ranges.Then,the near-infrared emissions are enhanced by co-doping Yb³⁺ions into the material.Based on that,the energy transfer process between Ho³⁺-Yb³⁺is demonstrated and the temperature sensing performance of the sample with the strongest NIR emission intensities is analyzed.The results of this paper have reference value for further research on the luminescence properties of rare earths and the development of optical temperature sensing materials.The contents of this paper are as follows:Firstly,Na YF₄:Ho³⁺NPs are prepared by the co-precipitation method,and the fluorescence concentration quenching phenomenon of Ho³⁺is analyzed.In this material,447 nm is the most efficient excitation according to the excitation and emission spectra.Under the excitation of 447 nm,the influence of different Ho³⁺doping concentration on luminescence performance is explored.Based on that,the energy transition of each emissions and the cross-relaxation process which affects the concentration quenching are analyzed.Secondly,Na YF₄:3%Ho³⁺NPs exhibiting strong emissions in both VIS and NIR ranges are selected to study the effect of temperature on emission intensities.The temperature-dependent emission spectra are measured from 113 K to 473 K and the physical mechanism of emission intensities changing with temperature is analyzed.Combining the comparison of the emission performance of Na YF₄:3%Ho³⁺NPs and Na YF₄:3%Ho³⁺@Na YF₄ NPs,non-radiative transition is regarded as the main reason for thermal quenching.The experimental results show that Na YF₄:3%Ho³⁺NPs present good temperature sensing performance in both visible and NIR ranges.The best absolute temperature sensitivity and relative temperature sensitivity can reach 0.0995 K^-1 and0.93%K^-1,respectively,which show excellent performance in Ho³⁺doping optical temperature sensing materials.Lastly,Ho³⁺-Yb³⁺doped Na YF₄ nanoparticles are prepared by co-precipitation method.The effects of different Yb³⁺doping concentrations on the emission properties of Na YF₄:3%Ho³⁺,x%Yb³⁺(x=0,1,3,5,7,10)are analyzed.The energy transfer process of Na YF₄:Ho³⁺,Yb³⁺NPs is analyzed by combining emission spectra and luminescence decay curves.The experimental results indicate that the emission enhancement in the NIR band is mainly caused by the efficient energy transfer process between Ho³⁺-Yb³⁺.The results show that the co-doped of Yb³⁺can improve the NIR emission intensities of this material and the best NIR emission intensities are achieved in the Na YF₄:3%Ho³⁺,3%Yb³⁺NPs with an enhancement factor of 18.However,since the energy transfer process between Ho³⁺and Yb³⁺is not sensitive to temperature changes,which means the incorporation of Yb³⁺ions weaken the temperature sensitivity,and resulting in weaker temperature sensing performance of Na YF₄:3%Ho³⁺,3%Yb³⁺.