ransparent glass-ceramics are still on the top in the field of functional photonic materials used in optical fiber technology. Generally, the glass-ceramic (GC) material consists of glass and suspended in amorphous volume nanocrystals doped with lanthanide ions. The controlled degree of crystallization is carried out in the process of heating materials at a specified temperature and at the right time of the experiment. Due to this, the glass-ceramic optical waveguide structures thus get better emission parameters (high quantum efficiency) compared to analogous amorphous structures, while maintaining the high optical quality. Nowadays, the GC optical fibers technology is complicated and consist many steps, wherein each stage of the experiment the material is thermal treated (melting → bulk annealing → drawing fibers → heat-treatment). As a result, this process is very complex and controlling the size and density of nanocrystals is difficult.
In our work we focused on the possibility to develop glass-ceramic optical fibers by one-step fabrication process. This is an innovative approach to the issue of nucleation, as well as to the growth of nanocrystals during the cooling of the vitreous mass. In fact, the crystallization process control through selecting the rate of cooling from the supercooled liquid zone during optical fibre drawing has not yet been investigated systematically. The influence of selected crystallization mechanism (nucleation and growth rates) on luminescent properties of GC is a kind of alternative approach to the currently used multi-step methods. Our experiment opens new possibilities for obtaining transparent glass-ceramic optical fibers with a high-density of nanocrystals embedded in their structure.
In the paper, 1.4 – 2.2 μm broadband emission under 796, 808, 980 nm laser diode excitation in low phonon energy germanate glass system co-doped with 0.7Er2O3/0.35Tmo2O3 (1st core) and 0.7Tm2O3/0.15Ho2O3 (2nd core) were investigated. Next, double-core, double-clad optical fiber has been developed by the modified rod-in-tube technique. Amplified spontaneous emission (ASE) in double-clad optical fiber with 3dB bandwidth was measured to be 346 nm and 677 nm for - 10 dB. ASE spectrum is a result of the partial donor-acceptor energy transfer and superposition of Er3+: 4I13/2 → 4I13/2, Tm3+: 3F4 → 3H6, 1.8 μm and (Ho3+:5I7 → 5I8) 2 μm emission bands. Excellent spectroscopic properties indicate that the developed germanate optical fiber is a promising active element for construction compact, broadband ASE sources.
In this work, thermal and luminescent properties of lithium-borate glass and glass-ceramics co-doped with Eu3+/Dy3+ and Eu3+/Tb3+ ions have been investigated. The parent borate glasses were synthesized by the standard melt-quenching method. The amount of crystallites grown in the glass was controlled by the appropriate choice of annealing time and temperature. Stronger luminescence has been observed for glass-ceramics than for glass in each case. Zinc lithium borate (LiBZnF) glass-ceramics co-doped with 0.25Eu and 0.5Tb had the strongest luminescence under 388 nm laser excitation. The energy transfer mechanisms between Tb3+ and Eu3+ ions and Dy3+ and Eu3+ ions were discussed. Also, the influence of the molar ratio of active ions on the colour coordinates (CIE-1931) have been investigated.
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