Cutoff wavelength effect

The valence and conduction band edges in the Pbj, Snj,Te alloys have the same many-valley form and nearly equal effective masses [4.3,34]. The cutoff wavelength at 77 K vs alloy composition in Pbi Sn,Te in the range of compositions normally used for detectors (0[Pg.137]

In LC, a means of detection is employed for identification and quantification. While detection is covered elsewhere in this volume, mobile phase selection can play an important role in the detectability of the compounds of interest, and vice versa. A solvents lowest usable (cutoff) wavelength is important for UV detectors, solvent refractive index (RI) effects the sensitivity of RI detection, and solvent volatility is an important consideration for evaporative light scattering and mass spectrophotometric based detectors. Table 4 lists some common LC mobile phase spectral data. 

As is well known, the recoil-free fraction of very small crystals differs markedly from that of bulk material. Roth and Horl [236] observed a decrease of the/-factor from 0.61 to 0.57 in going from 1 p,m crystals to microcrystals with a diameter of about 60 A. Two effects will contribute to this decrease (1) the low frequency cutoff, because the longest wavelength must not exceed the dimensions of the crystal, and (2) high frequency cut-off caused by the weaker bonds between surface atoms. 

Table I lists a variety of organic nonlinear materials which have appeared in the literature their relative powder efficiencies, absorption cutoffs and /3 values (if available) are also provided. These materials are "typical" only in that they represent results from the few classes of organic compounds investigated to date, yet they are instructive in that one learns which molecular properties may be important. A few caveats are in order to avoid misinterpretation of the data in Table I. Except for compound 10 (19) all the powder efficiency and cutoff data are from our own measurements. Powder measurements were performed on ungraded samples using the Nd YAG output at 1.06/t as fundamental since powder efficiency is a function of particle size distribution and a variety of other factors (3) these values are only semiquantitative. The cutoff values are the wavelengths for which 10-4M solutions in ethanol (unless otherwise indicated) have no absorbance. The cutoff values will be similar to those found in crystal state except where intermolecular charge transfer is important in the crystal or the molecule is solvatochromic, this latter effect being quite common for cyanine dyes such as...

Figure 3.21. Effective index of TE and TM optical modes in a thin film of spiro-sexiphenyl on a glass substrate at the amplified spontaneous emission (ASE) wavelength. Note the different cutoff thicknesses that determine the number of possible modes for a certain film thickness. 

Our earlier work with a polar silica gel column had demonstrated the need for a solvent of higher dielectric constant, i.e. methylene chloride, to effectively elute the cannabinoids. Methylene chloride could not be used at 209 nm due to its UV cutoff at 230 nm. The other partner in the earlier used gradient program, heptane, was compatible with use for lower wavelength monitoring because of its 200 nm cutoff. 

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