Fabrication And Luminescent Properties Of Rare Earth Doped Glass Ceramics Containing Sr₂YF₇Nano-Crystals

In recent years, rare earth ions (REI) doped luminescent materials have been attracting extensive attention due to their potential applications in three dimensional displays, solar cells, temperature sensors, white light-emitting diodes, scintillating and upconversion materials. Among the most glass ceramics, oxyfluoride glass ceramics may be an ideal bulk hosts for REI doping because they combine the advantages of low phonon energy environment of fluoride nano-cyrystals and excellent chemical and mechanical stability of oxide glasses. The main contents of this paper are focused on the fabrication and luminescent properties of rare-earth doped self-crystallized glass ceramics containing Sr2YF7 nano-crystals. Compared with conditional glass ceramics, self-crystallized glass ceramics have the advantages of easy fabrication, time-saving and realization of desirable nano-crystal size and activator partition. The main contains are listed as follows:1. Luminescence and energy transfer (ET) in self-crystallized Ce3+/Tb3+ co-doped glass ceramics containing Sr2YF7 nano-crystals:A series self-crystallized Ce3+/Tb3+ co-doped Sr2YF7 GC were successfully elaborated via melt-quenching method. Sr2YF7 nano-crystals precipitated directly without further heat-treatment. All GC samples possess highly transparent, which favors their practical applications. Effective ET from Ce3+ to Tb3+ was observed through fluorescence spectrum and ET mechanism from Ce3+ to Tb3+ was proved to be dipole-dipole interaction. Tunable emissions from blue to white and eventually to yellowish green were achieved by changing Tb3+ content. In addition, white light was obtained in GCCeT0.4 under the excitation of 312 nm light. Our results reveal that this new kind of inorganic material may serve as a potential photo-converter for white LEDs under UV LED excitation.2. The upconversion properties of self-crystallized Sr2Y(1-x)YbxF7:Er3+:Er3+-doped Sr2Y(1-x)YbxF7 glass ceramics were successfully elaborated via melt-quenching method. The content of Yb3+has a strong influence on the properties of Er3+. Some intense diffraction peaks are obviously observed in all GC samples without further heat-treatment, it indicated nano-crystals had been formatted during melt-quenching process. TEM bright-field image clearly shows that spherical nano-crystals, visible as dark spots, are homogeneously dispersed in amorphous glassy phase. As the absorption cross section of Yb3+ around 980 nm is larger than Er3+, the upconversion intensity of Er3+ was enhanced drastically after doping Yb3+. What is more, the green intensity of Er3+ is enhanced stronger than red with the increase content of Yb3+. Tunable emissions from green to yellow and finally into red could be achieved by appropriately changing Yb3+ concentration.