VISIBLE-REGION DEVICES

For Reflectance-mode operation, the simple expedient of inserting a mirror behind the entire apparatus may be used, or a more complex and unique structure with the working electrode facing the incident light may be used, as described in many issued patents and patent applications [892-896], 

It is noted that for both Transmittance- and Reflectance-mode operation, the performance of CP devices is not affected by viewing angle, an important advantage over their closest competitors, liquid crystal devices. 

Liquid electrolytes used may be aqueous, for example aqueous acidic (e.g. 0.2 M HCl or H2SO4) electrolytes used typically for P(ANi), or they may be nonaqueous, for example propylene carbonate (PC) or acetonitrile (ACN) (e.g. 0.2 M LiC104 in PC, with C104 the dopant) used typically for P(Py) or P(3MT). 

In addition to the possible provision of a non-electrochromic counter electrode reaction, several studies have incorporated an electrochromic counter electrode to supplement the electrochromism of the CP. These have a complementary color change (they darken when the CP lightens, etc.). Examples of this include prussian blue and WO3 glasses the latter use the cation of the dopant/electrolyte, e.g. Li of LiC104, in the electrochromic reaction. 

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The He-Ne laser described above is basically a single-frequency device and therefore its resolution is useful primarily as a frequency or dimensional standard. Tunable dye lasers have been devised, however, which operate in the visible region and have linewidths approaching 100 Hz. More common lasers, readily available commercially, have resolution (frequency/linewidth) in the range of 10 to 10°. 

In these polymeric species, the M,AT2-1,2,4-triazole linkage is rigid, and allows an efficient transmission of cooperative effects. Consequently, abrupt ST with broad thermal hysteresis loops have been observed [26, 32-34]. The absorption spectra of these compounds show a broad band at 520 nm corresponding to the Aig Trg d-d transition in the LS state whereas no band is found in the visible region in the HS state, the 5T2g-5Eg transition being located around 850 nm [7a]. The ST is thus accompanied by a thermochromic effect, purple (LS) and white (HS). These characteristics make these compounds potential candidates for practical applications, e.g. thermal display devices [7, 8, 17]. Such behaviour has been observed, for example, in the compound [Fe(4-amino-l,2,4-triazole)3](NC>3)2 [32] whose SCO is associated with a hysteresis loop of width 35 K, centred above room temperature [8]. 

This UV radiation is converted into visible radiation by means of the fluorescence of the phosphor powder coating. The phosphor material uses the UV radiation as an excitation source and produces fluorescent emission in the visible region, with a broad spectrum to give off the white light that we can see. A good variety of combinations of phosphors are used (Shionoya and Yen, 1999). The principal field of application of fluorescent lamps is general lighting, for which they constitute efficient devices. 

Triarylmethane Dyes with Near-Infrared Absorption. The long wavelength absorption bands of triarylmethane dyes can be shifted into the near-infrared region, but the dyes still remain colored because other absorption bands are shifted to or stay in the visible region. These types of triarylmediane dyes and their derivatives have been claimed as infrared absorbers for optical information recording media and security devices, and as organic photoconductors for nse in lithographic plate production. 

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