Preparation And Luminescent Properties Of Rare Earth Doped GdPO₄Glass Ceramics

The research content of this dissertation is consisted of three chapters. The first chapter is a general introduction to the relevant knowledge and research advances. Chapter2describes the preparation methods, characterization techniques and cautions during the controllable crystallization of glass ceramics (GC). In chapter3, we report the fabrication, structural and transmittance characterization of novel Yb3+/Er3+co-doped transparent glass ceramics containing GdPO4nanocrystals as well as their luminescent properties. We also analyze the potential applications in the field of luminescent thermometry for Yb3+/Er3+co-doped GdPO4transparent GCThe relevant knowledge and basic concept of luminescence materials have been presented in the introduction firstly. Then, a brief introduction to upconversion materials, quantum cutting materials, phosphors for white LED as well as GC was given in the following paragraph. Finally, we also indicate that the purpose of our research is to fabricate a novel Yb3+/Er3+co-doped GdPO4transparent GC which combines the advantages of GdPO4:Yb3+, Er3+multifunctional fluorescent magnetic nanocrystalline and GC materials, and investigate its properties.In chapter2, we introduce three main processes related to the preparation of GC including selection of raw materials, melt and controllable crystallization. In addition, cautions related to the preparation process of GC were discussed in detail. Our analyses suggest that the appropriate selection of raw materials and design of component are precondition for the formation of PG. The homogeneity and distribution of nanocrystals in GC were directly determined by the heat treatment process. A brief introduction to the relevant characterization methods was given at the end of chapter2.The main research works of this dissertation are described and discussed in chapter three. The luminescent properties of Yb3+/Er3+co-doped GdPO4transparent GC were investigated under different conditions. The specific research content and results can be summarized as follows:1. Yb3+/Er3+co-doped transparent GCs containing GdPO4nanocrystals have been successfully fabricated using a melt-quenching method with subsequent heat treatment. Their structure and morphology were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). A large quantity of GdPO4nanocrystals emerge for GC after a heat treatment process and the crystallinity of GC increased with the rise of temperature. Based on the XRD patterns and HRTEM image, the average size of GdPO4nanocrystals was estimated to be23nm. According to the transmittance spectra of PG and GC, GC still maintains a perfect transparency due to the smaller size of precipitated GdPO4nanocrystals compared to the wavelength of visible and near-infrared light.2. The luminescent properties of Yb3+/Er3+co-doped GdPO4transparent GC heat-treated at640℃(GC640) and670℃(GC670) as well as PG were analyzed in detail. Under the ultraviolet excitation (378nm), the total luminescent intensity of the samples reduced in order of PG, GC640, GC670, indicating that rare earth ions have entered into GdPO4nanocrystals whose phonon energy is higher than that of base glass during crystallization. Under the excitation of a980nm diode laser, the average Yb-Er distances reduced because of the concentration of rare earth ions in GaPO4nanocrystals, leading to the improved energy transfer from Yb3+to Er3+and thus a stronger unconverted emission. The intensity of upconverted emission will also increase with an improved crystallinity. In addition, we found that the Green/Red emission intensity ratio in the GC670sample was enhanced compared to that in the PG and GC640. Contrasting with the non-radiative transition (corresponding to red emission), the efficiency of cross-relaxation, energy transfer and excited state absorption process (corresponding to green emission) will be more strongly dependent on the population number of4I11/2state. Therefore, the main reason for the above phenomenon is that the population of4I11/2state of Er3+is larger due to higher upconvertion efficiency for GC670sample with better crystallization and the intensity of green emission increased faster when the population of4I11/2state increased. Under the excitation of a980nm diode laser, the intensity of infrared emission of GC is weaker than that of PG on account of the complementation relationship between infrared emission and upconverted emission. We also find that the optimum doping concentration for the strongest intensity of upconversion emission is25%Yb3+,2%Er3+.3. The upconverted emission of GaPO4:25%Yb3+,2%Er3+GC sample heat-treated at670℃was investigated under different pump power densities and temperatures in the rage of295-535K. As a result of the variation of the population number of4I11/2state with pump power density, the Green/Red emission intensity ratio of the samples also changed with the increase of pump power density. On the other hand, the measured intensities of the green emission of2H11/2â†'4I15/2transition at523nm and green emission of4S3/2â†'4I15/2transition at545nm of Er3+vary diffenertly with temperature as the populations of the two well-known thermal-coupled2H11/2and4S3/2multiplets are determined by the Boltzmann distribution. The fluorescence intensity ratio (FIR) of the emission bands centered at523nm and545nm were recorded at different temperatures, the dependence of FIR on absolute temperature for GaPO4:25%Yb3+,2%Er3+GC can be well-fitted with an exponential function, and the effective energy difference obtained from the fitting is713cm-1. The relative sensitivity of the sample is1.18%K-1at295K. This result provides potential applications in the field of luminescent thermometry for Yb3+/Er3+co-doped GdPO4transparent GC.