Optical Transition Characteristics And Luminescence Thermal Stability Of Rare Earth Doped NaYF₄ Luminescent Materials

With the rapid development of the national economy,people have put forward higher requirements for materials used in lighting,metallurgy,transportation,shipping and biomedicine.Rare earth doped NaYF4 nanoparticles have excellent optical properties and stable chemical properties,low toxicity and large Stokes displacement,which makes them have rapid development and wide applications in temperature probes,photoelectric displays,biological imaging,fluorescent probes and biosensors.Therefore,using NaYF4 doped with different rare earth elements as the matrix material,biomedical probe materials and lighting materials were synthesized by different synthetic methods.Their photo thermal conversion performance,temperature sensing characteristics and optical transition characteristics were explored as follows:(1)The NaYF4:Dy3+/Yb3+@NaYF4:Er3+/Yb3+core-shell nanostructures were synthesized by high-temperature pyrolysis.The temperature sensing,fluorescence temperature quenching and photothermal conversion performance were studied.The measurement of fluorescence intensity ratio(FIR)shows that the NaYF4:Er3+/Yb3+shell structure has good performance in temperature detection and readout.At the same time,it was also confirmed that the main reason for the temperature quenching of the green fluorescence of Er3+is that the probability of non-radiative transition of the 4S3/2 state increases with temperature.In addition,based on the experimentally determined temperature sensing of the shell structure,the photothermal conversion was further studied.It is proved that the core-shell nanoparticles can effectively convert the excitation light energy into thermal energy.(2)Sm3+doped NaYF4 crystals doped with different concentrations were synthesized by self-combustion assisted fluorination.The crystal,structure of the phosphor was detected by X-ray diffraction(XRD),and it was confirmed that NaYF4:Sm3+was a pure phase.The spectrum shows the dependence of the excitation wavelength on the Sm3+ doping concentration.The electric dipole to electric dipole interaction(D-D)has been proved to be the main mechanism of energy transfer between Sm3+,and is confirmed again on the basis of the Van Uitert model.The optical transition characteristics of NaYF4:Sm3+were studied within the framework of Judd-Ofelt(J-O)theory.The radiative transition rate and intrinsic lifetime of the transition energy level of interest were obtained.The fluorescence emission with temperature was further studied in detail.It was found that the Crossover process based on the Arrhenius model can well explain the fluorescence temperature quenching behavior of the 4G5/2.2 energy level.(3)The self-combustion assisted fluorination method was used to successfully synthesize NaYF4:Dy3+crystals doped with different concentrations.The pure phase of ?-NaYF4 was determined by XRD and scanning electron microscopy(SEM),Further observation of the excitation spectrum and emission spectrum revealed the effect of Dy3+doping concentration on light intensity,and based on the Van Uitert model,it was confirmed that D-D is the mechanism of Dy3+ energy transfer.By calculating the yellow-to-blue ratio(Y/B)of NaYF4:Dy3+fluorescent particles and further exploration of the color coordinates,the choice of materials for white light LED provides opportunities and new development.