Spectra optical line emission

A host material is activated with a certain concentration of Ti + ions. The Huang-Rhys parameter for the absorption band of these ions is 5 = 3 and the electronic levels couple with phonons of 150 cm . (a) If the zero-phonon line is at 522 nm, display the 0 K absorption spectrum (optical density versus wavelength) for a sample with an optical density of 0.3 at this wavelength, (b) If this sample is illuminated with the 514 nm line of a 1 mW Ar+ CW laser, estimate the laser power after the beam has crossed the sample, (c) Determine the peak wavelength of the 0 K emission spectrum, (d) If the quantum efficiency is 0.8, determine the power emitted as spontaneons emission. 

At a high enough temperature, any element can be characterised and quantified because it will begin to emit. Elemental analysis from atomic emission spectra is thus a versatile analytical method when high temperatures can be obtained by sparks, electrical arcs or inert-gas plasmas. The optical emission obtained from samples (solute plus matrix) is very complex. It contains spectral lines often accompanied by a continuum spectrum. Optical emission spectrophotometers contain three principal components the device responsible for bringing the sample to a sufficient temperature the optics including a mono- or polychromator that constitute the heart of these instruments and a microcomputer that controls the instrument. The most striking feature of these instruments is their optical bench, which differentiates them from flame emission spectrophotometers which are more limited in performance. Because of their price, these instruments constitute a major investment for any analytical laboratory. 

The ICP has proliferated as a method of converting chemical compounds into their elemental constituents which subsequently emit light of characteristic wavelengths. Accordingly, ICP has been used extensively as an emission source for optical detection systems in order to perform elemental analysis. Since each element can emit hundreds of optical lines, the use of ICP/AES for multiple element analysis, or for the detection of elements in unknown or concentrated matrices, can suffer from interferences due to spectral overlap. By contrast, ICP-MS provides inherently simpler spectral Information. An example of such a spectrum is demonstrated in Figure 2 showing a typical ICP-MS scan for a 10 ug ml"l solution of mixed transition metals. The demonstrated sensitivity here is 10 to 10 counts s l per ug m1"l and, coupled with the nearly universal ionization efficiency of the ICP ion source, provides typical detection limits in a narrow range between 0.1 to 10 ng.ml" for most elements. In fact over 90% of the elements in the periodic table are accessible for such analytical determinations. 

Molecules in the collisionally populated levels m) can decay by the emission of fluorescence or by further collisions. In the LIF spectrum new lines then appear besides the parent lines, which are emitted from the optically pumped level (Fig. 8.7). These new lines, called collision-induced satellites contain the complete information on the collision process that has generated them. Their wavelength X allows the assignment of the upper level m) = + An, 7 + A7), their intensities yield... 

In Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), a gaseous, solid (as fine particles), or liquid (as an aerosol) sample is directed into the center of a gaseous plasma. The sample is vaporized, atomized, and partially ionized in the plasma. Atoms and ions are excited and emit light at characteristic wavelengths in the ultraviolet or visible region of the spectrum. The emission line intensities are proportional to the concentration of each element in the sample. A grating spectrometer is used for either simultaneous or sequential multielement analysis. The concentration of each element is determined from measured intensities via calibration with standards. 

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... 

Qualitative analysis may be made by searching the emission spectrum for characteristic elemental lines. With modem high resolution optics and computer control, the emission spectrum may be readily examined for the characteristic lines of a wide range of elements (Figure 8.13). Quantitative measurements are made on the basis of line intensities which are related to the various factors expressed in equation (8.1). Under constant excitation... 

Excitation of sample atoms by primary radiation from a high-intensity broad spectrum or element selective source. Samples atomized in a chemical flame using a circular burner. Optics to isolate emission line and photomultiplier to measure its intensity. 

A certain transition metal ion presents two optical absorption bands in a host crystal whose zero-phonon lines are at 600 nm and 700 nm, respectively. The former band has a Huang-Rhys parameter 5 = 4, while for the latter 5 = 0. Assuming coupling with a phonon of 300 cm for the two bands (a) display the 0 K absorption spectrum (absorption versus wavelength) for such a transition metal ion (b) display the emission spectra that you expect to obtain nnder excitation in both absorption bands and (c) explain how you expect these two bands to be affected by a temperature increase. 

The optical emission spectrum of technetium is uniquely characteristic of the element " with a few strong lines relatively widely spaced as in the spectra of manganese, molybdenum and rhenium. Twenty-five lines are observed in the arc and spark spectra between 2200 and 9000 A. Many of these lines are free from ruthenium or rhenium interferences and are therefore useful analytically. Using the resonance lines of Tc-I at 4297.06, 4262.26, 4238.19, and 4031.63 A as little as 0.1 ng of technetium can be reliably determined. 

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