Infrared Ray Absorbents

Phthalocyanines typically exhibit absorption in the red region of the spectrum. It is therefore relatively easy to make phthalocyanine compounds absorb near infrared radiation by molecular modification. For example, the introduction of elec- 

Such soluble phthalocyanine compounds can be dissolved in polymer films, and used as a near infrared ray absorbent of sunlight. Two interesting appUcation fields have been proposed, as a shield of heat rays [7] and as a controller of plant growth in agriculture [8]. 

Heat radiation can be absorbed by films containing phthalocyanine compounds and transformed into an excited state. When the excitation energy can be relaxed by nonradiative transitions, in a vibration-relaxation process, the excitation energy is used to raise the temperature of the phthalocyanine compounds, which is then diffused into the surrounding air through the films. Such materials can be applied to the windows of buildings and automobiles. About 90% of the heat in the automobile is estimated to come in from its windows. These materials are believed to cut about 50% of heat radiation. 

The most successful application of near infrared radiation absorbing phthalocyanine compounds is in material for recordable compact discs (CD-R). According to the international standard specification, recording materials for CD-R must have an absorption maximum around 780 nm, which wavelength permits both recording and read out. The thickness, refractive index, and extinction coefficient of the recording material are all optimized to increase the reflectance of the recording layer. 

Mitsui Chemicals and Ricoh employ such phthalocyanine compounds for their CD-R products. Compared with cyanine dyes, usually pentacyanine dyes, phthalocyanine compounds are excellent in light fastness and in performance for high rate recording, but are much more expensive. Evaluation results of commercially available CD-Rs by consumers are available from Internet websites. In order to increase the demand for phthalocyanine compounds in the recording materials of CD-R, cost reduction appears the most significant hurdle to overcome. 

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Diiminium compounds can be synthesized from the corresponding amine, silver nitrate, and (1). These are near-infrared ray-absorbing compounds, which are free from antimony and arsenic, and show excellent stability, particularly with regard to heat resistance, light stability, and moist heat resistance. 

A bolometer is essentially a thin blackened platinum strip in an evacuated glass vessel with a window transparent to the infrared rays it is connected as one arm of a Wheatstone bridge, and any radiation absorbed raises the temperature of the strip and changes its resistance. Two identical elements are usually placed in the opposite arms of a bridge one of the elements is in the path of the infrared beam and the other compensates for variations in ambient temperature. Both the above receptors give a very small direct current, which may be amplified by special methods to drive a recorder. 

Direct absorptiometry is subject to several uncertainties the seriousness of which is greatly mitigated if x-ray absorbance of the unknown (sample) can be properly established relative to that of a standard.21 The advantages of comparative absorptiometry at longer. wavelengths (e.g., infrared) are well known they are, if anything, greater when x-rays are used. 

The energy band diagram in the range of n-type region 15, p-type layer 12, p-type layer 11 and p-type layer 12 is shown above. Carriers excited by the infrared ray of 3-5 microns wavelength band absorbed below the electrode 19 are detected at between the electrode 19 and the common electrode 17. 

Amorphous plastics, such as acrylics, are transparent to infrared rays. Some semiciystalline polymers, such as PFA, have surprisingly high levels of infrared transmission. PFA can be welded by infrared under certain circumstances. For example, a transparent tube of PFA was welded to a black sheet of PFA that absorbed the infrared light generated by aNd YAG laser (1,064 nm).P8] a tube composed of natural PFA (6.4 mm outer diameter and 3.2 mm inner diameter) was pressed into a 6.4 mm diameter hole in an aluminum sheet. The aluminum sheet was used to shield the black PFA sheet from stray radiation. The IR light was defocused to a diameter of 6.4 mm and aimed at the end of the tube in the aluminum. A laser power of 30 W with a tube length of 50 mm produced a strong weld in a few seconds. 

Infrared spectroscopy is a technique based on the vibrations of atoms of a molecule. In order to get a spectrum, the sample is placed in a sample holder and then an infrared ray is passed through the sample. The signals or peaks that can be appreciated in an IR spectmm correspond to the energy absorbed by the sample at specific frequencies that depend on the molecule s structure. To detect a signal, molecules must change their electric dipole during irradiation, which implies the generation of specific movements between atoms and chemical bonds [4]. 

PM-IRRAS exploits the different attenuation of s- and p-polarized light by adsorbed species at a reflective (electrode) surface to annul the unchanging contributions to the infrared signal at the detector from the solvent, window, and so on, and produces an absolute rather than difference spectrum at a particular potential. In this approach, a photo-elastic modulator is employed to modulate the polarization state of the incident infrared ray between s- and p-states. On the basis of Greenler s theory [81, 82], this polarization modulation gives rise to an AC signal at the detector, which is proportional (/p —7s)-the difference in intensity of the two polarizations. Since, in principle, /p is absorbed... 

Figure 1.6 shows the specular reflectance spectra of A1 coated and uncoated surfaces of the film 1. A1 coated surface reflected 100% of the infrared rays since the absorbance values were very close to zero. Uncoated surface had the characteristic spectrum of polypropylene. However, there were other peaks observed called fringes due to reflection of light from both surfaces of the thin film. 

Climate change CO2, CH4 and other GHG released into the environment allow sunlight to pass through the Earth s atmosphere, but absorb the infrared rays that reflect off land and water. This inhibits their escape and therefore heats up the atmosphere... 

Colorimetry, in which a sample absorbs visible light, is one example of a spectroscopic method of analysis. At the end of the nineteenth century, spectroscopy was limited to the absorption, emission, and scattering of visible, ultraviolet, and infrared electromagnetic radiation. During the twentieth century, spectroscopy has been extended to include other forms of electromagnetic radiation (photon spectroscopy), such as X-rays, microwaves, and radio waves, as well as energetic particles (particle spectroscopy), such as electrons and ions. ... 

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