Crystallization kinetics and spectroscopic investigations on Tb3+ and Yb3+ codoped glass ceramics containing CaF2 nanocrystals

Abstract

Transparent Tb 3+ and Yb 3+ codoped oxyfluoride glass ceramics containing CaF 2 nanocrystals were prepared by melt quenching and subsequent heat treatment. Crystallization kinetics of CaF 2 nanocrystals was investigated by differential scanning calorimetric method. The average apparent activation energy E a of the crystallization was ϳ498 kJ/ mol. Moreover, the value of the Avrami exponent n was 1.01. These results suggest that the crystallization mechanism of CaF 2 is a diffusion controlled growth process of needles and plates of finite long dimensions. X-ray diffraction patterns and transmission electron microscopy image confirmed the CaF 2 nanocrystals in the glass ceramic. Ultraviolet ͑UV͒ and visible emission spectra of the as-made glass and the glass ceramic with an excitation of a 974 nm laser diode were recorded at room temperature. An intense UV emission at 381 nm was observed in the glass ceramic. The origin of the enhancement of the emission at 381 nm was investigated using spectroscopic technique and Judd-Ofelt analysis. The enhancement of the emission at 381 nm could be attributed to the change of the ligand field of Tb 3+ ions due to the incorporation of some Tb 3+ and Yb 3+ ions into CaF 2 nanocrystals in the glass ceramic.

Highly matched spectrum needed for photosynthesis in Ce3+/Er3+/Yb3+ tri-doped oxyfluoride glass ceramics

“…The mean particle size calculated by Scherrer formula is about 25 nm. The lattice constant of the nano-crystals in the present glass ceramics was about 5.505 A˚, larger than that of the pure CaF 2 crystal (a=5.462A˚ [24]). Therefore, the Yb 3+ ions are considered to be incorporated into the CaF 2 to form Ca 0.8 Yb 0.2 F 2.2 solid-solution crystals containing trivalent lanthanide ions.…”

Luminescence behavior of Tb3+ ions in transparent glass and glass-ceramics containing CaF2 nanocrystals

“…The as-made glass has the highest transparency, the transparency of glass-ceramics gets slightly lower with the increase of heat-treatment temperature. The faster nucleation and growth rate of CaF 2 nanocrystals in glass-ceramics can be confirmed with the elevated heat-treatment temperature, resulting in the larger size and higher crystallization fraction, but these glass-ceramics still retains good transparency, since the nanosize of CaF 2 is much smaller than the wavelength of the visible light [11,12].…”

“…The volume fraction of the crystalline phase (crystallinity) in the glass ceramic was estimated by the ratio of integrating the area of the peaks and the total area of the XRD pattern from 101 to 601 [6,11]. The crystal size and the volume fraction of CaF 2 nanocrystals in glass-ceramics were plotted as a function of heat-treatment temperature in Fig.…”

“…However, the cost of LaF 3 materials is an obstacle for its practical application, some relative nanocrystals such as NaYF 4 and Sr 2 GdF 7 have been precipitated in transparent glass-ceramics [9,10]. The transparent glass-ceramics containing MF 2 (M ¼ Ca, Sr and Ba) nanocrystals recently have been aroused more interest owing to both the lower cost and less poison of MF 2 raw materials [11][12][13][14][15][16][17]. Furthermore, crystalline CaF 2 is highly transparent from 0.13 to 9.5 mm and gives a better matching of refractive index with the aluminosilicate glassy host [15].…”

Enhanced green upconversion luminescence in Yb–Tb co-doped sintered silica nanoporous glass

“…-doped silicate fibers [4,5]. Upconversion luminescence (UCL) in rare-earth (RE)-doped materials can be an efficient mechanism to overcome the above problems and obtain visible (VIS) and near-infrared (NIR) laser [6][7][8]. Usually, there are two kinds of rare-earth ions in UCL materials: one kind of ions act as donor, and another kind of ions act as acceptor; upon pumping with lower-energy photons, the donors will be excited to excited states, and then they will transfer their absorbed energy to acceptors by energy transfer mechanisms [9].…”