Preparation And Luminescence Of Rare Earth Doped NaY（Gd）F₄ Oxyfluoride Glass Ceramics

With the continued development and the wide application of new materials, glass ceramics have attracted great attention. Especially, oxyfluoride glass ceramics does not only have low phonon energy environment of fluoride crystals, but also have the high thermal and chemical stability of oxide glass network. Oxyfluoride glass ceramics rapidly become a research focus in rare earth doped glass ceramics.Base on the research of aluminosilicate glass, after heat-treatment, rare earth doped Na YF4, Na Re F4(Re=Y/Gd), Na Gd F4 oxyfluoride glass ceramics were synthesized. Samples were investigated by DT A, XRD, CT E, TEM, STEM, FTIR and PL. For the structure, the glass framework, thermal stability, mechanism of crystallization, crystal p hase, and morphology were analyzed. For the properties of luminescence, the intensities and life time of luminescence was measured. T he mechanisms of radiation were analyzed.Dy3 + doped, Dy3 +/T b3 + co-doped transparent aluminosilicate glass and glass ceramics were prepared by conventional the melt quenching method and following heat-treatment. The crystal phase: α-Na YF4 was confir med by XRD results. T he nanocrystals were distributed homogeneously in residual glass phase. Dy3 + doped samples showed the blue and yellow emission under the excitation of 350 nm. After heat-treatment, the value of Y/B ratio changed, obviously. The Dy3 + and T b3 + concentrations were regulated to control the intensities of different emissions. Consequently, the white-light emission was obtained under 386 nm excitation.The crystal phase evolution from α-Na YF4 to β-Na YF4 was successfully achieved by modifying oxyfluoride glass composition and impurity doping in the glass ceramics. T he mechanism of transition was analyzed by FT IR, XRD and TEM results. Eu3 + ions were introduced to analyze the influence of phase transformation on luminescence and were proved incorporated into Na Y(Gd)F 4 nanocrystals. T he emission intensites of Er3 +/Yb3 + co-doped glass ceramics were measured. Compared with the α-Na YF4 glass ceramic, the intensities of the emissions in β-Na YF4 glass ceramic increased for 200 times.Dy3 + doped, Dy3 +/Ce3 + co-doped, Dy3 +/T m3 + co-doped aluminosilicate glass and glass ceramics were obtained by melt quenching method and following heat-treatment at 600, 650, 700, 750 and 800 oC, respectively. T he crystallite size, crystal phases and structrue were confirmed by XRD, TEM and ST EM results. T he glass ceramic heat-treated at 700 oC was analyzed by EDS. T he result indicated that the nanocrystals were surrounded by the Si-riched shells after heat-treatment. T he peak ascribed to Si O 2 was detected in the XRD pattern of glass ceramic heat-treated at 750 oC. In addition, the FTIR results also confirmed the existence of the shells. T he glass transition temperatures(T g) and softening temperature(T f) are obtained in the CTE curves. By VFT equation, the viscosity-temperature relation was calculated. The viscosity of residual glass phase improved during the c rystallization of modifier ions. Concentration dependent emission spectra of glass ceramics were measured. T he quenching concentration of Dy3 + was 0.5mol%. Owing to the energy transfer process: Ce3 +â†'Dy3 +, white-light emission was obtained with the CIE(0.315, 0.334) by varying the ratio of Dy3+/Ce3 + concentration in co-doped glass ceramic. Owing to the energy transfer process: Dy3 +â†'Tm3 +,white light emission was obtained with the CIE(0.320, 0.332) by varying the ratio of Dy3 +/T m3 + concentration in co-doped glass ceramic. T hese co-doped glass ceramics exhibited great potential application on W-LEDs under UV-excitation.