Mercury discharge lamp

Until the advent of lasers the most intense monochromatic sources available were atomic emission sources from which an intense, discrete line in the visible or near-ultraviolet region was isolated by optical filtering if necessary. The most often used source of this kind was the mercury discharge lamp operating at the vapour pressure of mercury. Three of the most intense lines are at 253.7 nm (near-ultraviolet), 404.7 nm and 435.7 nm (both in the visible region). Although the line width is typically small the narrowest has a width of about 0.2 cm, which places a limit on the resolution which can be achieved. 

Air or water cooled mercury discharge lamps find many uses, one of the more obvious of which is the study of photochemical reactions. These lamps are usually made of vitreous silica because of its low thermal expansion, high melting point and its transparency to ultraviolet radiation. Their operating pressure has a profound effect on the spectral distribution of the radiation produced and therefore it is important to consider the requirements in the design of such lamps. 

Irradiation of a 2,4-D sodium salt solution by a 660-W mercury discharge lamp produced 2,4-dichlorophenol within 20 min. Continued irradiation resulted in continued decomposition. The irradiation times required for 50% decomposition of the 2,4-D sodium salt at pH values of 4.0, 7.0, and 9.0 are 71, 50, and 23 min, respectively (Aly and Faust, 1964). 

The wavelength scale may also be calibrated according to the spectral lines of deuterium or mercury discharge lamps and such tests may be built into some instruments. 

Ultraviolet sources are chiefly mercury-discharge lamps in various forms. These lamps are fragile and quite inefficient. The design of reactors using these lamps is hampered by these considerations, and by the limited ultraviolet transmission, of common glasses and solvents. The transmission is further decreased by coatings of opaque materials which form... 

For many years halophosphates were quantitatively by far the most important group of phosphors for low-pressure mercury discharge lamps (fluorescent lamps). The number of studies on the optimization of the quantum yield of halophosphates is correspondingly large. The most important work on the properties and production technology has been reported, for example in [5.345], [5.370]. 

Figure 4- Target Current vs. Target Potential Mercury Discharge Lamp Induced Photoelectrons...

FAB SIMS in conjunction with charge neutralization utilizing mercury discharge lamp induced photoelectrons permits low-damage highly reproducible analysis of electrically insulating surfaces. Stable spectra can be obtained from polymeric materials such as polyethylene for periods of an hour or more. Minor spectrum differences between samples such as the various oxides of cobalt, which may have previously been due to thermal or surface potential effects, can now be more confidently assigned to compositional differences. 

Emission Spectrum. Several sources are suitable for exciting the emission spectrum of I2. In previous editions of this text, the use of a low-pressure mercury discharge lamp was described, in which the green Hg line at 546.074 nm causes a transition from... 

Fig. 55. Schematic representation of a fluorimeter 1 mercury discharge lamp, 2 diaphragm, 3 lens. 4 heat filter, 5 primaiy filter, 6 cuvette, 7 secondary filter, 8 photodetector, 9 measurement at an angle of 90° to the incident light.

Mercury discharge lamp Metal halogen bulb Pliotoflash light... 

Electrodes in fluorescent lamps (coated W or NS-W). Fluorescent lamps are low-pressure mercury discharge lamps which radiate in the UV region. The ultraviolet radiation is converted into light by means of a fluorescent layer (phosphor). Tungsten coils, coated with a mixture of Ca, Ba, and Sr compounds, are used as electrodes (emitter). 

Experimental details.12 9 A solution of 457 (0.74 mmol) and triethylamine (2 mmol) in methanol was purged with nitrogen for 1 h and irradiated in a Rayonet photochemical chamber equipped with 16 low-pressure mercury discharge lamps (254nm) (Figure 3.10) for 12h. After irradiation, methanol was distilled off under reduced pressure and the product was purified by column chromatography in 90% chemical yield. 

Experimental details.1503 A mixture of the monomer 579 (1 3 mg) and a photoinitiator ( 3 wt%) in a sample (open-air) cell was irradiated with a high-pressure mercury discharge lamp (200 W) (Figure 3.11). In order to prevent evaporation of the monomer, the cell was covered with a thin poly(ethylene terephthalate) film. The extent of polymerization was evaluated by differential photocalorimetry. 

Figure 18.7 Mercury analysis. Two models of analyzers (Reproduced courtesy of Mercury Instr. USA and Genesis Laboratory Systems Inc.). The mercury concentration is measured in an optical cell made of fused silica on the path of a mercury discharge lamp(253.7 nm resonance line). Mercury is measured either by AAS or FAS.

The fluorescent lamp is basically a low pressure mercury discharge lamp with a layer of phosphor particles on the inside surface of the glass tube, as shown in 6.6.6., presented on the next page. 

At one time, the progress in the field of Raman spectroscopy of polymers was heavily dependent upon laser technology. The advent of accessible laser sources made it possible to replace the mercury-discharge lamp as an excitation source. Other developments, such as photomultipliers, computerization, or, most recently, sensitive array detectors made a tremendous impact on applications of this method in polymer analysis. 

Fig. 19.16. Experimental setup of a flowthrough quartz photoreactor used for photocatalytic decomposition in aqueous Ti02 dispersions using cylindrical electrodeless mercury discharge lamps. A, cylindrical EDL...

Low-pressure mercury discharge lamps are not only used for lighting. Since it is in principle possible to have a phosphor with every wavelength desired, there are many, more specialized applications. Here we mention a few. 

While some of the mid-IR sources emit light below 400 cm the intensity drops off. A more useful source for the far-IR region is the high pressure mercury discharge lamp. This lamp is constructed of a quartz bulb containing elemental Hg, a small amount of inert gas, and two electrodes. When current passes through the lamp, mercury is vaporized, excited. 

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