Laser Induced Thermal Effect On Upconversion Luminescence Of Rare Earth Doped Gd₂（WO₄）₃ Phosphors

As well known, phosphors are used in many fields of peoples’daily lives, such as light-converted LEDs, fluorescent lamps, CRT monitors and so on. In recent years, the upconversion luminescence phosphors become a hot spot in the scope of solid state luminescence materials owing to the practical applications in various fields. In order to obtain highly efficient and practically applicable rare earth ions doped upconversion luminescence phosphors, effects have mainly devoted to the preparative routes, control of particle sizes, doping design, concentration quenching and host matrix and so on. However, the influence of temperature on the upconversion luminescence properties is an interesting and impracticable topic and has rarely noticed due to the fact that the real temperature of phosphor surface is difficult to be detected; meanwhile, the upconversion behaviors of rare earth ions doped materials may be affected by many factors, one of which is the sample temperature which is hardly be investigated individually. Taking above-mentioned facts into account, this dissertation focuses on the upconversion luminescence in temperature-sensitive Ho3+ Tm3+ and Er3+ doped Gd2(WO4)3 phosphors when excited at 980 nm. The main results are listed as follows.1. Gd2(WO4)3:Yb3+/Ho3+ phosphors were synthesized by use of a co-precipitation methord. Under near-infrared 980 nm excitation, the red and green upconversion luminescence of Ho3+ions were observed. The laser induced thermal effect on the upconversion luminescence of Gd2(WO4)3:Yb3+/Ho3+ phosphors were analyzed for the first time by means of time scan spectra. The UC luminescence of Gd2(WO4)3:Yb3+/Ho3+ phosphor at different powers of excitation source and sample temperatures was studied. It was found that under high excitation power the thermal quenching phenomena occurred for the red and green UC emissions, and at room temperature the red and green UC emissions were 1.5- and 2- photon process, respectively. With increasing sample temperature the 2-photon process for the red UC emission and 3-photon process for green UC emission occurred.2. Gd2(WO4)3:Yb3+/Er3+ and Gd2(WO4)3:Yb3+/Tm3+ phosphors were also prepared by use of the co-precipitation method. The laser induced thermal effect on upconversion luminescence were again observed firstly in Gd2(WO4)3:Yb3+/Tm3+ phosphors. In Gd2(WO4)3:Yb3+/Er3+ phosphor, two green UC emission coming from 2H11/2 and 4S3/2 states of Er3+ were observed, and the ratio of their luminescent intensities present temperature dependence, and the relationship between the ratio and temperature was obtained. The Gd2(WO4)3:Yb3+/Er3+ phosphors used as thermal probe were mixed with Gd2(WO4)3:Yb3+/Tm3+ phosphors, and the temperature variation of Gd2(WO4)3:Yb3+/Tm3+ phosphors under 980nm excitation were measured and discussed.