Lamp emission spectra

Lamp Emission Spectra. Figure 2 shows the emission lines from 200-600 nm of a Fusion H medium pressure mercury arc lamp operating at 300 W/lnch. Although emission spectra are normally plotted as Energy vs wavelength, we have utilized the Stark Einstein relation to convert energy to intensity, which is proportional to the number of photons emitted at each wavelength. 

Figure 2-14 Neon lamp emission spectrum. Band numbers refer to Table 2-8 in (a) and Table 2-9 in (b).

Silicate, nickel, and cobalt tend to interfere in the air-acetylene flame, although nickel and cobalt are rarely present in sufficient excess to cause a problem. Silicate interference may be eliminated at modest excesses by the use of lanthanum as a releasing agent or by using a nitrous oxide-acetylene flame. Very careful optimization is sometimes necessary, for example in the analysis of freshwaters, when concentrations are very low. It is important to use a narrow spectral bandpass and to make sure that the correct line is being used, because the hollow cathode lamp emission spectrum of iron is extremely complex. If you have any doubts about monochromator calibration, check the sensitivity at adjacent lines ... 

An explanation of the differences in cure rate between DPI and TPS is less obvious, as the absorption spectra of these two compounds are -similar. Depending on the method of preparation, however, the TPS photoinitiator frequently shows some absorbance in the spectral region between 290 and 340 nm, overlapping the band at 310 in the mercury lamp emission spectrum. This may be the result of a fortuitous contaminant not completely removed in synthesis and purification of the TPS photoinitiator. 

Rate of Emission of Photons by the UV Lamp The rate of emission of photons by the lamp, so-called lamp characterization can be developed in the LTU, as described in Chapter III. In the LTU, a radiometer is placed at a fixed distance form the lamp s axis. A radiomenter correction factor of 1.41 (equation 3-1) is used which relates the tnie absolute reading to the lamp emission spectrum and the radiometer normalized spectral response. Thus the radiometric measurement allowed for the determination of the spatial distribution of the lamp radiative flux, qe y i. 

Regai ding X, it can be obtained iteratively from the lamp emission spectrum and the following relationship ... 

Figure 17-5. Setup for the measurement of absorption losses in a 3D waveguide as a function of wavelength, by reference to the lamp emission spectrum.

The emission spectrum from a hollow cathode lamp includes, besides emission lines for the analyte, additional emission lines for impurities present in the metallic cathode and the filler gas. These additional lines serve as a potential source of stray radiation that may lead to an instrumental deviation from Beer s law. Normally the monochromator s slit width is set as wide as possible, improving the throughput of radiation, while being narrow enough to eliminate this source of stray radiation. 

Whereas the emission spectrum of the hydrogen atom shows only one series, the Balmer series (see Figure 1.1), in the visible region the alkali metals show at least three. The spectra can be excited in a discharge lamp containing a sample of the appropriate metal. One series was called the principal series because it could also be observed in absorption through a column of the vapour. The other two were called sharp and diffuse because of their general appearance. A part of a fourth series, called the fundamental series, can sometimes be observed. 

Continuous sources The sources of choice for measurements in the ultraviolet spectral region are hydrogen or deuterium lamps [1]. When the gas pressure is 30 to 60 X10 Pa they yield a continuous emission spectrum. The maxima of their radiation emission occur at different wavelengths (Hi A = 280 nm Di 2 = 220 nm). This means that the deuterium lamp is superior for measurements in the lower UV region (Fig. 15). 

The Effect of Light Source on Curing Rate. As stated earlier, Sylvania F4T5 was the lamp used in the standard Photo-DSC measurements and this lamp had a broad emission spectrum centered at 350 nm. When an alternate lamp (GE F4T5) with an emission peak at 365 nm was used, the ranking of initiators, in terms of peak time, remained the same. Table III lists representative results from these experiments. The emission spectrum of this GE lamp was also shown in Figure 3. 

Fluorescent lamps generate light through a low-pressure mercury vapor discharge that has strong emission tines in the UV, namely at A = 254 nm and around 366 nm. The fluorescent layer is excited by the UV radiation and emits in the visible part of the spectrum. While remains of the 254 nm tine are efficiently rejected by the glass tube, some fraction of the 366 nm radiation can be measured in the emission spectrum of the lamp. 

An emission spectrum for pure mercury obtained from a mercury lamp. It is easy to see that mixed sources, and higher energy excitation will produce very complex patterns of lines, demanding high quality optical... 

Radiation is derived from a sealed quartz tube containing a few milligrams of an element or a volatile compound and neon or argon at low pressure. The discharge is produced by a microwave source via a waveguide cavity or using RF induction. The emission spectrum of the element concerned contains only the most prominent resonance lines and with intensities up to one hundred times those derived from a hollow-cathode lamp. However, the reliability of such sources has been questioned and the only ones which are currently considered successful are those for arsenic, antimony, bismuth, selenium and tellurium using RF excitation. Fortunately, these are the elements for which hollow-cathode lamps are the least successful. 

A convenient method is the spectrometric determination of Li in aqueous solution by atomic absorption spectrometry (AAS), using an acetylene flame—the most common technique for this analyte. The instrument has an emission lamp containing Li, and one of the spectral lines of the emission spectrum is chosen, according to the concentration of the sample, as shown in Table 2. The solution is fed by a nebuhzer into the flame and the absorption caused by the Li atoms in the sample is recorded and converted to a concentration aided by a calibration standard. Possible interference can be expected from alkali metal atoms, for example, airborne trace impurities, that ionize in the flame. These effects are canceled by adding 2000 mg of K per hter of sample matrix. The method covers a wide range of concentrations, from trace analysis at about 20 xg L to brines at about 32 g L as summarized in Table 2. Organic samples have to be mineralized and the inorganic residue dissolved in water. The AAS method for determination of Li in biomedical applications has been reviewed . 

One often unsuspected source of error can arise from interference by the substances originating in the sample which are present in addition to the analyte, and which are collectively termed the matrix. The matrix components could enhance, diminish or have no effect on the measured reading, when present within the normal range of concentrations. Atomic absorption spectrophotometry is particularly susceptible to this type of interference, especially with electrothermal atomization. Flame AAS may also be affected by the flame emission or absorption spectrum, even using ac modulated hollow cathode lamp emission and detection (Faithfull, 1971b, 1975). 

Forbes, P. D., R. E. Davies, L. C. D Aloisio, and C. Cole, Emission Spectrum Differences in Fluorescent Blacklight Lamps, Pho-tochem. Photobiol., 24, 613-615 (1976). 

The most frequently used lamp for UV curing processes is medium-pressure mercury lamp. Its emission spectrum can be used to excite the commonly used photoinitiators. Moreover, this type of lamp has a relatively simple design, is inexpensive, can be easily retrofitted to a production line, and is available in lengths up to 8 ft (2.5 m). Power levels in common use are in the range 40 to 240 W/cm, and even higher levels are available for special applications. ... 

Doped lamp Term applied to a UV mercury lamp containing metal halide added to the mercury to alter the emission spectrum of the lamp (preferred term is additive lamp). 

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