Optical Properties of Glass-Ceramics

We know that, in the best cases, Ln + ions are segregated in the crystallites. In this section we will discuss and compare the optical properties (absorption, emission, lifetime) of glass-ceramics, glasses and single-crystals. Throughout the section, we will see the con- 

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Thermal, Mechanical, and Optical Properties. The unusual and in some cases unique thermal, mechanical, and optical properties of glass-ceramics have contributed much to their commercial success. Almost all of these properties relate to the characteristics of the crystalline phases, and to their microstructural arrangement. 

In this chapter, we describe different transparent oxyfluoride systems doped with lanthanide ions. We examine the conditions that can lead to a perfectly controlled crystallization process and also the conditions that insure an efficient segregation of the rare-earth ions inside crystallites. Finally, we discuss the optical properties of glass-ceramics, in terms of absorption, emission and lifetimes. We establish a comparison between their optical properties and those of glasses and single-crystals. 

In addition, the segregation of Ln into the fluoride crystallites induces a strong local Ln " " concentration inside the crystallites, which also affects the optical properties of glass-ceramics as it is discussed hereafter. 

Comparison of the Optical Properties of Glass-Ceramics and Single-Crystals... 

As previously described, the optical properties of glass-ceramics are rather different from those of the precursor glasses. In this paragraph, a comparison is made between the spectroscopic characteristics of glass-ceramics and those of single-crystals. 

As part of powder beneficiation, compositional modification may also be performed by the addition of second phases, dopants, etc. These changes may be required to influence the sintering behavior of the ceramic powders or to tailor the structural, thermal, electrical, and optical properties of the ceramic products. The source of these additives may be from powders such as oxides, glasses, or salts. To remove unwanted impurities, second phases, surface contaminants, or other by-products, powders may beneficiated by washing, sedimentation, filtration, and magnetic separation. 

E. J. Friebele, in Optical Properties of Glass, Ed. D. R. Uhlmann and N. J. Kreidl, American Ceramic Society, Westerville, OH, 1991, Chapter 7. 

An experiment with a dilute ceramic suspension was made as follows A very small quantity of silicon carbide particles (d 6 /xm) was dissolved in silicon oil ( 350mPas). The suspension was pumped at high pressure through a glass capillary (d = 0.6 mm). The experimental setup is shown in Fig. 3. The velocities of the silicon carbide particles in the capillary are detected by an optical sensor. From these data, the statistics of the particles velocities is calculated. Due to the optical properties of the sensor, the particles are only detected in a wedge-like sector of the cross-section of the capillary. The measured velocity distribution of the particles (Fig. 4) depends on the shape of this sector and, additionally, on the measuring tolerances of the sensor. 

T. Suzuki, K. Floribuchi, Y. Ohishi, Structurl and optical properties of Zn0-Al203-Si02 system glass-ceramics containing Ni -doped nanoceystal, J. Non-Crys. Soilds, 351, 2304 (2005). 

The mechanical, optical, and electrical properties of glasses are discussed in detail, along with other ceramics, in those topical chapters. 

The optical properties of ceramics result in some of their most important applications. In their pure form, most dielectric single crystals and glasses are transparent to visible light. This behavior is very different from that of metals and semiconductors, which, unless they are very thin (<1 pm), are opaque. Many ceramics and glasses also show good transparency to infrared (IR) radiation. This property has led to the use of glasses for optical fibers for high-speed communications. 

Kingery, W.D., Bowen, H.K., and Uhlmann, D.R. (1976) Introduction to Ceramics, 2nd edition, Wiley, New York. Chapter 13 covers the optical properties of ceramics and glasses. 

Combining polymers with inorganic glass formers has recently been used to form ceramers [27]. These hybrid materials show many desirable properties for example, the optical properties of polymers, and the hardness/wear of glass. 

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