Zaijin Fang

Efficient spectral conversion from visible to near-infrared in transparent glass ceramics containing Ce3+–Yb3+ codoped Y3Al5O12 nanocrystals

Transparent glass ceramics containing Ce3+–Yb3+ codoped Y3Al5O12 nanocrystals were prepared, and their microstructures were characterized by X-ray diffraction and transmission electron microscopy. Intense near-infrared emission at around 1000 nm, attributed to the 2F5/2 → 2F7/2 transition of Yb3+, was observed upon excitation at 452 nm. Efficient energy transfer from Ce3+ ions to Yb3+ ions was confirmed by the luminescence spectrum and fluorescent lifetime measurements; the mechanism was investigated and demonstrated to be a single-photon process rather than a two-photon process. Greatly enhanced near-infrared emission was achieved from the glass ceramics excited by simulated sunlight from 400 to 800 nm compared with that from as-prepared glass. These results demonstrate that the glass ceramics are promising materials for spectral conversion from visible sunlight to near-infrared emission and may have potential applications as spectral convertors to enhance the photoelectric conversion efficiency of c-Si solar cells.

Ni(2+) doped glass ceramic fiber fabricated by melt-in-tube method and successive heat treatment.

Glass ceramic fibers containing Ni(2+) doped LiGa(5)O(8) nanocrystals were fabricated by a melt-in-tube method and successive heat treatment. Fiber precursors were prepared by drawing at high temperature where fiber core glass was melted while fiber clad glass was softened. After heat treatment, LiGa(5)O(8) nanocrystals were precipitated in the fiber core. Excited by 980 nm laser, efficient broadband near-infrared emission was observed in the glass ceramic fiber compared to that of precursor fiber. The melt-in-tube method can realize controllable crystallization and is suitable for fabrication of novel glass ceramic fibers. The Ni(2+)-doped glass ceramic fiber is promising for broadband optical amplification.

Precisely controllable fabrication of Er3+-doped glass ceramic fibers: novel mid-infrared fiber laser materials

We demonstrated remarkably enhanced 2.7 μm emission in glass-ceramic (GC) fibers containing NaYF4:Er3+ nanocrystals with 980 nm excitation for the first time. The melt-in-tube technique is of scientific and technical significance for the fabrication of GC fibers in comparison to the conventional rod-in-tube technique. The obtained precursor fibers, in which the structure can be maintained well, exhibit no obvious element diffusion or crystallization during the fiber-drawing process. After a careful heat treatment, NaYF4 nanocrystals were controllably precipitated in the glass fiber core. Owing to the incorporation of Er3+ ions into the low phonon energy NaYF4 nanocrystals, enhanced 2.7 μm emission was achieved from the Er3+-doped GC fibers, which was almost undetectable in precursor fibers due to the high phonon energy of the borosilicate glass fiber matrix. Moreover, the 2.7 μm emission lifetime was obtained due to the excellent emission properties of Er3+ in the GC fibers. The transmission loss values of precursor fibers and GC fibers at 1310 nm were measured to be 7.44 dB m−1 and 11.81 dB m−1, respectively. In addition, a theoretical simulation based on the rate equations and propagation equations was performed to evaluate the possibility of 2.7 μm laser output. The excellent optical properties endow the GC fibers with potential applications for mid-infrared fiber lasers.

Enhanced upconversion emission in crystallization-controllable glass-ceramic fiber containing Yb3+-Er3+ codoped CaF2 nanocrystals

Functional nanocrystal-containing materials have been a hot topic in recent years. However, few researches have focused on functional nanocrystals contained in optical glass fibers. In this research, transparent CaF2 glass-ceramic was prepared by a melt-quenching method. Greatly enhanced upconversion luminescence was observed after heat treatment. By applying a novel method called melt-in-tube, precursor fiber free of crystals was fabricated at the drawing temperature where the clad was softened while the core was melted. Glass-ceramic fiber with fiber core containing Yb(3+)-Er(3+) codoped CaF2 nanocrystals was obtained after heat treatment at a relatively low temperature. Electron probe micro-analyzer measurement shows no obvious element diffusion between the core and clad. Greatly enhanced upconversion emission was detected in the glass-ceramic fiber excited by a 980 nm laser, suggesting the developed glass-ceramic fiber is a promising material for upconversion laser.

Formation, element-migration and broadband luminescence in quantum dot-doped glass fibers

All solid-state PbS quantum dot (QD)-doped glass precursor fibers avoiding crystallization during fiber-drawing process are successfully fabricated by melt-in-tube technique. By subsequent heat treatment schedule, controllable crystallization of PbS QDs can be obtained in the glass precursor fibers, contributing to broad near-infrared emissions from PbS QD-doped glass fibers. Nevertheless, we find that element-migration and volatilization of sulfur simultaneously happen during the whole fiber-drawing process, because of the huge difference between the melting temperature of core glass and the fiber-drawing temperature. Element-migration pathways along the fiber length were revealed. Such PbS QD-doped glass fiber with broadband emissions will be a potential application as gain medium of broadband fiber amplifiers and fiber lasers.

Controllable fabrication of novel all solid-state PbS quantum dot-doped glass fibers with tunable broadband near-infrared emission

All solid-state PbS quantum dot (QD)-doped glass fibers with tunable near-infrared (NIR) emission were successfully fabricated by using the “melt-in-tube” method for the first time. The precursor fibers were first prepared without any obvious element diffusion or crystallization by drawing the fiber preform at a heating temperature at which the fiber core was already melted while the fiber cladding was softened. Then the PbS QDs were precipitated evenly in the matrix of the glass fiber core after a careful heat treatment at low temperature. From the PbS QD-doped glass fibers, intense wavelength-tunable broad NIR emission bands were observed upon excitation with an 808 nm laser. The transmission loss of the fibers can be reduced by further matching the thermal expansion of the fiber core and cladding glass. Therefore, after further optimizing the composition and optical properties of the PbS QD-doped glass fiber, it is expected to be a potential gain medium for the development of wavelength-tunable lasers and broadband fiber amplifiers. More importantly, the melt-in-tube method exhibits a feature of completely controllable crystallization in the fiber formation process, which would open a new route for fabricating novel functional QD-doped glass fibers.