Optical properties of pigments

This section will discuss some important concepts from coloristic practice and the optical properties of pigmented systems. Space considerations permit a treatment of only the most vital concepts. The reader must consult the literature for further details and accounts of special problems [1], A review on the effect of crystal structure on color application properties was published [2],... 

The effect of particle size on optical properties of pigments is described in Section 1.3. 

Figure 4. The relationships between the optical properties of pigments and their theoretical basis...

These coefficients have the dimension of reciprocal length (Mills, 1988), in this context, cm Kubelka and Munk (1931) described the optical properties of pigments by employing the parameters a and r. The Kubelka-Munk theory is the basis of diffuse reflection spectroscopy (Sec. 6.4). We have extended the Kubelka-Munk approach in order to describe the Raman scattering of crystal powders (Schrader and Bergmann, 1967). The results can also be applied to liquids and transparent solids. The procedure is as follows ... 

Garcia-Uribe, A., et al. In-vivo characterization of optical properties of pigmented skin lesions including melanoma using oblique incidence diffuse reflectance spectrometry. Journal of Biomedical Optics 16(2), 020501 (2011)... 

Because of their insolubility, pigments are used in the form of dispersed submicron particles. Interfacial and scattering properties of the pigment particles determine their in-use and optical properties. As a consequence, the optical properties of pigments can be controlled by the size and the shape of their particles. 

The optical properties of pigments in the near infrared were studied by Taylor Di Bernardo reported anomalous spectrophotometric behavior of copper phthalocyanine—benzidine yellow mixtures. Brode and Wyman presented the absorption spectra of ten thio-indigo dyes in benzene and chloroform and discussed the effect of irradiation upon their cis-trans equilibria they also presented the spectra of nine of these dyes in H2SO4 in the range 210-800 m/i. 

Design of structure—property functions for single particles and particle ensembles. Both gradually become accessible if their structure is not too complex. Promising examples are the shape design of pharmaceutical crystals or optical properties of pigment particles (see Example 3 in Section 5.3 (Taylor et al, 2011)). 

The value of pigments results from their physical—optical properties. These ate primarily deterrniaed by the pigments physical characteristics (crystal stmcture, particle size and distribution, particle shape, agglomeration, etc) and chemical properties (chemical composition, purity, stabiUty, etc). The two most important physical—optical assets of pigments are the abiUty to color the environment in which they ate dispersed and to make it opaque. 

The chapters cover the following areas (i) use of coordination complexes in all types of catalysis (Chapters 1-11) (ii) applications related to the optical properties of coordination complexes, which covers fields as diverse as solar cells, nonlinear optics, display devices, pigments and dyes, and optical data storage (Chapters 12-16) (iii) hydrometallurgical extraction (Chapter 17) (iv) medicinal and biomedical applications of coordination complexes, including both imaging and therapy (Chapters 18-22) and (v) use of coordination complexes as precursors to semiconductor films and nanoparticles (Chapter 23). As such, the material in this volume ranges from solid-state physics to biochemistry. 

Gorton, H.L. and Vogelmann, T.C., Effects of epidermal cell shape and pigmentation on optical properties of Antirrhinum petals at visible and ultraviolet wavelengths, Plant Physiol, 112, 879, 1996. 

Eller, B.M., Glattli, R., and Elach, B., Optical properties and pigments of sun and shade leaves of the beech (Fagus silvatica L.) and the copper-beech (Fagus silvatica cv. Atropunicea), Flora, 171, 170, 1981. 

Mie s Theory. Mie applied the Maxwell equations to a model in which a plane wave front meets an optically isotropic sphere with refractive index n and absorption index k [1.26]. Integration gives the values of the absorption cross section QA and the scattering cross section Qs these dimensionless numbers relate the proportion of absorption and scattering to the geometric diameter of the particle. The theory has provided useful insights into the effect of particle size on the color properties of pigments. 

Figure 15.2. Optical properties of conventional pigments, metallic pigments, pearl pigments and pearls.

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