IR emitter

The highest efficiency red emitters belong to the class of phosphorescent materials and are based on iridium organometallic complexes. The best performance achieved in guest-host systems, for example using a carbazole host and an Ir emitter (Ir(piq-F)2acac, has a maximum power efficiency and luminescent efficiency up to 4.73 lm/W and 13.7 cd/A, respectively. An EQE of 6.7% at 20 mA/cm2 with CIE (0.61, 0.36) has been demonstrated (Scheme 3.96) [361]. 

Fig. 4 Steady-state excitation and emission spectra for live distinct ssDNA encapsulated Ag clusters, (a) Blue emitters created in 5 -CCCTTTAACCCC-3, (b) green emitters created in 5 -CCCTCTTAACCC-3, (c) yellow emitters created in 5 -CCCTTAATCCCC-3, (d) red emitters created in 5 -CCTCCTTCCTCC-3, and (e) near-IR emitters created in 5 -CCCTAACTCCCC-3. (f) Pictures of emissive solutions in (a)-(d) [46]...

Furthermore, grains are efficient infrared (IR) emitters and provide a cooling agent which, in the process of gravitational collapse of interstellar clouds into stars, very much facilitates star formation. 

Figure 13.11 PA-IR emittance spectra of a polystyrene film recorded at 120°C with acquisition times ranging from 870 to 17.4ms. Reproduced with permission from Ref [37].

Infrared radiation is another wave band of non-ionising radiation. The IR region is divided into IR-A (A 760-1440 nm), IR-B (A 1440-3000 nm) and IR-C (A 3000 nm-1 mm). The main source of IR radiation is the sun, but artificial IR emitters are constantly gaining importance. They are used for therapeutic as well as for lifestyle purposes, e.g. as a wellness source. 

Coumarin 2 has been paired as a donor with a diamino-substituted per-ylene near-IR emitter to produce a FRET-based UV to NIR frequency converter (Scheme 31) [92]. Excitation at the coumarin 2 A,max ( ex = 345 nm) resulted in FRET to the higher excited state (S ) of the perylene core. This state imdergoes rapid internal conversion to the first excited singlet state (Si, Kasha s rule), from which emission is observed. Comparison of the integrated donor emission in the absence of the core and in the target dendrimer indicated a 99% energy transfer efficiency, accompanied by a 6.2-fold increase in the core emission relative to the emission in the absence of peripheral donors. 

While the importance of cobalt-based pigments in ceramics is well established, it has also been shown that thin films of C03O4 provide an effective coating for solar collectors that operate at high temperatures. The properties of black C03O4 that make it suitable for this application are its high solar absorbance and low IR emittance. 

The thermal radiation heat-transfer rate, emitted by the IR emitter is equal to Aeo T, where A is the emitter... 

There are two basic types of IR heaters electric IR and gas-fired IR (Figure 46.16). The most important element of the IR drying system is the IR emitter. These two types of IR heaters fit into three temperature ranges (1) 343°C-538°C (e.g gas and electric IR) (2) 538°C-1100°C (e.g gas and electric IR) and (3) 1100°C-2200°C (e.g., electric IR only). Electrically heated or natural-gas-heated units are used mainly to preheat the web, although these can be used in principle to carry out the entire drying process. IR temperatures are typically in the 650°C-1200°C range. Improved drying rates can be obtained by a combined radiation-convection system. 

IR Panel Heaters. Better than direct IR heating is the secondary IR emitter panel (see Fig. 47.5). It is constructed out of metal or ceramic platens heated either conduc-tively via attached resistance heaters or by direct IR irradiation on the back side of the panel. 

A variant of this method is the convective IR oven. This technique also relies on radiant or panel IR heating, but the air in the oven is stirred by fans to enhance uniformity of heating. However, techniques such as IR lamp, IR emitter, and combination convective units have been largely supplanted by a more favorable method forced-air convection, where air is forced through the panel heaters at high velocity. This produces very even oven temperatures and rapid heating response and control. This method is the mainstay of oven reflow. 

The thermal radiation heat-transfer rate, rad, emitted by the IR emitter is equal to Aeo- T , where A is the emitter surface area, s is the emissivity of the emitter, cr is the Stefan-Boltzmann constant (5.67x10 W/m /K ), and T is the temperature of the emitter. As the energy emitted varies with the fourth power of temperature, the heating power... 

The so-called hybrid IR emitter combines a carbon emitter and a short-wave IR emitter (see Tab. 10.5) in a quartz-glass twin-tube configuration. This combination allows the use of IR heat in processes that require both short-wave and medium-wave IR radiation, and the result is homogenous heating, matched to the application. In contrast to pure carbon emitters, the voltage can be flexibly adjusted. 

---