Upconversion Spectroscopy Properties And Photo-thermal Mechanism Of Rare Earth Doped Sodium Yttrium Tungstate Phosphors

In recent years, the upconversion luminescence (UCL) properties of inorganic materials doped with rare earth (RE) ions have been investigated extensively due to their immense potential applications in many fields such as 3-dimentional displays, imaging of biological systems, temperature senators, etc. Many researchers’effects have mainly devoted to the synthetic method, control of particle sizes, and host matrix and so on by far. However, less attention has been paid to the rare earth ions’population at high temperature and photothermal conversion behavior. This is because the energy transfer rate is sensitively affected by temperature during the process of UCL, and the dynamic process varied very complex. Base on the above mentioned, the studies of this dissertation are focused on the UCL properties and photothermal behaviors in temperature-sensitive Tm3+/Yb3+ and Sm3+/Nd3+doped NaY(WO4)2 microstructures when excited by fiber laser. The main results gotten by the author are listed as follows:1. Under excitation at 980 nm, the optimum doping concentration of Tm3+ for the highest blue and NIR UCL was investigated, and the temperature effect on blue and NIR upconversion luminescence was studied. It was found that the optimal concentration for blue and NIR emission was 0.5 mol% and 1.5 mol%, respectively, and the sample with lower Tm3+concentration displayed more obvious effect on the thermal quenching of 1G4 level.2. The laser induced photothermal behavior in NaY(WO4)2:Tm3+/Yb3+ micostructures were firstly investigated by NaY(WO4)2:Er3+/Yb3+temperature probe. It was found that higher laser excitation density resulted in higher sample temperature, and the sample with higher Tm3+doping concentration exhibited more obvious heating effect when excited by 980 nm fiber laser. Moreover, the time scanning upconversion spectra displayed that the upconversion luminescence intensities for both the samples with low and high Tm3+concentrations almost unchanged with 980 nm laser irradiation time when the excitation power density was lower, but decreased greatly when the excitation power density was higher, and the sample with low Tm3+concentration displayed larger luminescence intensity change rate. This phenomenon was explained by Arrhenius’s model for the thermal quenching process.3. The laser induced photothermal behavior in NaY(WO4)2:Tm3+/Yb3+ micostructures was investigated by using NaYF4:Er3+/Yb3+ temperature probe. It was found that the energy transfer can achieved between the Sm3+ ions and Nd3+ ions under the excitation at 808 nm. And the non-radiative transition results in the heating effect of Sm3+ ions depends on the pump power and Sm3+ doping concentration. The higher pump power and doping concentration, the more obvious for photothermal conversion behavior.