Luminescent glass-ceramics

Other Aluminosilicates, Transparent mullite glass-ceramics can be produced from modified binary Al C —Si02 glasses (21). In these materials, the bulk glass phase separates into tiny alumina-rich droplets in a siliceous matrix. Further heat treatment causes these droplets to crystallize to mullite spherulites less than 0.1 Jim in size. When doped with ions such as Cr3+, transparent mullite glass-ceramics can be made to absorb broadly in the visible while fluorescing in the near-ii (22,23), thereby making them potentially useful for luminescent solar collectors. 

The importance of transparent glass-ceramics doped by Cr as potential new materials for luminescent solar concentrators and tunable lasers is considerable It has been shown that Cr(III) exhibits exceptionally high quantum efficiency of luminescence in these materials as compared to glasses of the same compositions . Cr is also used as a probe for nucleation of and crystallization of cordierite into glass-ceramics . ... 

Reisfeld, R. Potential uses of Cr(III) doped transparent glass-ceramics in luminescent solar eoncentrators. Report Series Swedish Academy of Engineering Seienees in Finland (Helsinki) 40, part I (Proc. Advaneed Summer School on the Eleetronie Strueture of New Materials, Loviisa, August 1984) pp. 7-34, Helsinki 1985... 

Reisfeld, R., J0rgensen, C. K. Cr(III) broad-band quartet-quartet luminescence in glass-ceramics with higher yield than in complexes. King, E. L., Busch, D. H., Sievers, R. E. (eds.). Abstracts of 23. Int. Conf. Coordination Chemistry, Boulder CO 1984, p. 162... 

Use Ceramics and porcelain glazes, pharmaceuticals, catalyst, other lithium compounds, coating of arc-welding electrodes, nucleonics, luminescent paints, varnishes and dyes, glass ceramics, aluminum production. 

We think that MCD studies on glass ceramics, where the lanthanides are imbedded in a cubic structure, could provide useful supplementary information on the luminescence properties. 

Confocal micro-luminescent has been developed to analyze the optical changes produced by exciting the sample with an argon laser. The emission of the Er I11/2 -> and I13/2 -> I15/2 transitions are reported and shown structural differences after the femtosecond irradiation. The lifetimes of the levels involved in these transitions are measured inside and outside the damaged area. These measurements are compared with the bulk glass ceramic sample to estimate the optimal condition to produce nanocrystals in a localized area. 

Fujita S, Sakamoto A, Tanabe S (2008) Luminescence characteristics of YAG glass-ceramic phosphor for white LED. Selected topics in quantum electronics. IEEE J Sel Top Quantum Electron 14(5) 1387... 

Tanabe S, Fujita S, Yoshihara S, Sakamoto A, Yamamoto S (2005) YAG glass-ceramic phosphor for white LED (II) luminescence characteristics. In Proceedings SPIE fifth international conference on solid state lighting 5941 594112... 

Furthermore, Andrews et al. (1986) were able to incorporate Cr ions into these very small mullite crystals to produce luminescent properties. Reisfeld et al. (1984) and Kiselev et al. (1984) have reported about the luminescent properties produced by Cr. Section 4.3.3 describes why luminescent mullite glass-ceramics, for example, are preferred in solar and laser technology. Selected properties of these glass-ceramics are listed in Table 2-6. 

It must be noted at this point that transparent PbTiO glass-ceramics are of interest for electro-optic and electro-luminescent applications (Kokubo and Tashiro, 1976). Non-transparent, opaque PbTi03 glass-ceramics, however, can be used for thick-film capacitors with a dielectric constant of 94 and tan 6 of 0.0130 (at 10 c/s) on alumina substrates that have been heated to temperatures up to approximately 600°C. The dielectric constant of the capacitor as a function of temperature is almost linear from room temperature to 270 C, with a temperature coefficient of 0.00083 K Therefore, it was found that glass powders were suitable for preparing capacitors with a high dielectric constant (Kokubo and Tashiro, 1976). 

In solar engineering, sunlight is transformed into other useful forms of energy, such as electricity. For this purpose transparent materials may be desired. At the same time, these materials must enable the transfer of energy. Glass-ceramics can exhibit both high transmission and luminescent optical properties. 

For applications of this kind, mullite, 3Al203 2Si02, glass-ceramics with chromium ions as luminescent centers were developed (Beall 1992,1993). The composition of this glass-ceramic is described in Section 2.2.1 and the formation of its microstructure in Section 3.2.5. The special features of this material were developed on the basis of the applications described in this section. 

Apart from using this mullite glass-ceramic for luminescent solar concentrators, it was also intended for laser applications, such as gain media of high-power lasers. Both applications of the glass-ceramic require the development of similar properties. These properties are ... 

Silicon photovoltaic strips must be effectively bonded to the edges of the glass-ceramic sheet (window) to efficiently convert the near-infrared luminescence to electric energy. 

Tick et al. (1995) modified this system by adding Znp2 and YF and doping solely with the rare-earth ion Pr (Table 4-12) at the low level of 0.1 mol%. The luminescent quantum efficiency of Pr emission at the 1300 nm telecommunication band was measured at 7%, an improvement over similar Pr emission from the well-known fluoride glass, ZBLAN , measured at 4%. These glass-ceramics... 

In recent yeors, there has been an increasing interest in glass-ceramic applications where optical properties are key. A parallel but unrelated trend involves the use of glass-ceramics as dental and surgical prostheses. In the optical area, the most significant properties are in the near infrared range in combination with excellent transparency. Efficient broadband luminescence in crystallites is the basis of applications such as tunable lasers and optical amplifiers, both of which can be made in both bulk and fiber form as glass-ceramics. 

Dejneka M.J., "The Luminescence and Structure of Novel Transparent Oxyfluoride Glass-Ceramics,"/. Non-Cryst. Solids, 239, 149—55 (1998a). 

---