Optical properties of ceramics

The optical properties of ceramics are useful in the ultraviolet, visible, and infrared ranges of the electromagnetic spectrum, and one key quantity used to describe the optical property of a material is the refractive index, which is a function of the frequency of the electromagnetic radiation. Other quantities used to characterize optical performance are absorption, transmission, and reflection these three properties sum to unity and are also frequency dependent. The last three properties govern many aspects of how light interacts with materials in windows, lenses, mirrors, and filters. In many consumer, decorative, and ornamental applications, the esthetic qualities of the ceramic, such as color, surface texture, gloss, opacity, and translucency, depend critically on how light interacts with the material. 

To understand some of the optical properties of ceramics and why certain materials may be favored for solar cell or laser applications, we need to know whether the band gap is direct or indirect. The two situations are illustrated in Figure 4.25. The electrons in a band have both energy and momentum (they are not bound) expressed as a wave vector, k, with units of reciprocal length (usually cm ). Energy diagrams can be plotted for different wave vectors. 

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. 

Furuse H, Yasuhara R, Hiraga K (2014) Thermo-optic properties of ceramic YAG at high temperatures. Opt Mater Expr 4 1794-1799... 

The optical properties of ceramics are naturally affected either directly or indirectly by factors such as the constituent elements constituting the ceramic, the crystalline symmetry, the microstructure of the ceramic, and changes in the external field. Table 7.1.2 lists some of the typical factors that affect the optical properties of ceramics. Even in single crystals—which are the simplest form of ceramics under the broad definition—these factors rarely act individually on the optical properties. And in a polycrystalline material, the situation is obviously much more complicated. 

TABLE 7.1.2 Some Factors Reacting on the Optical Properties of Ceramics... 

A discussion of the optical properties of ceramics would be incomplete... 

Commercial instruments, such as the Lambda 19 (Perkin-Elmer Corp.), can be used for the measurement of the ultraviolet (UV), visible (VIS), and near-infrared (NIR) optical properties of ceramics. Such an instrument, when used in conjunction with the RSA PE 90 (Labsphere, Inc.) integrating sphere, can be used to measure the spectral reflectance of opaque ceramics. Commercial instruments are excellent for quality control and industrial and analytical analyses of ceramics. 

Electrooptic Properties, The electrooptic properties of the PLZT materials are intimately related to their ferroelectric properties. Consequently, varying the ferroelectric polarization with an electric field such as in a hysteresis loop, produces a change in the optical properties of the ceramic. In addition, the magnitude of the observed electrooptic effect is dependent on both the strength and direction of the electric field,... 

R. H. French, H. Mtlllejans, and D.J. Jones, "Optical properties of aluminum oxide Determined from vacuum ultraviolet and electron energy loss spectroscopies," J. Am. Ceram. Soc., 81, 2549-57 (1998). 

Material science can also benefit from oligomeric state of proteins. New retinal nano-ceramic materials with pillared hybrid micro-structures were fabricated for potential applications in optical holographic data storage. It was observed that the Schiff bases in retinal have substantial effect on optical properties of nano-ceramic films as well as diffraction efficiency for holographic storage. This study indicates feasibility of optimizing optical properties of nano-ceramic clay systems using Schiff bases for a variety of photonic applications.40... 

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. 

Suresh K. S. and James F. C., Optical properties of zinc aluminate, zinc gallate and zinc aluminogallate spinels, J. Am. Ceram. Soc. 81 (1998) pp. 649-654. 

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. 

Rare earth aluminates are also important commercially as ceramics and ceramic composites for scintillation applications. The importance of the optical properties of rare earth aluminates is underscored by the used of Nd-doped YAG as a laser host. 

A. Ikesue, T. Kinoshita, K. Kamata and K. Yoshida, Fabrication and Optical Properties of High-Performance Polycrystalline Nd YAG Ceramics for Solid-State Lasers, J. Am. Ceram. Soc., 78, 1033-40(1995). 

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