Raman crystal-field excitations

In the case of cubic crystal symmetry the T, and F symmetry components are Raman allowed. In fig. 15 the well known vibrations of the octahedra have been included to demonstrate the corresponding symmetry. The peak near 95 cm appears only in F symmetry with the Tj and F components being zero. The symmetry analysis is consistent with the identification of the 95 cm line as due to a crystal-field excitation, but does not allow a separation of the two transitions. 

Pr + ( H4), and Sm + ( H5/2) ions. These studies have revealed both pure crystal-field excitations in R2CUO4 systems, as well as crystal-field excitations in RBa2Cuj06 systems that derive their Raman intensities from a strong magneto-elastic coupling with phonons. For a more detailed discussion of these studies, the reader is referred to the recent review article by Cardona (1999). 

Wickham DG (1963) Use of lead pyrophosphate as a flux for crystal growth. J Appl Phys 33 3597-98 Williams GM, Becker PC, Conway JG, Edelstein N, Boatner LA, Abraham MM (1989a) Intensities of electronic Raman scattering between crystal-field levels of Ce in L11PO4 Nonresonant and near-resonant excitation. Phys Rev B 40 4132-4142... 

Such kind of Ct + luminescence is rather typical for natural forsterite. For example. Figure 5.44 presents luminescence features of several forsterite samples detected drrring Raman spectra study (http //rruff.info). Luminescence bands peaking at 740-750 nm rmder excitation by 532 nm at 300 K may be ascribed to Cr + in intermediate and strruig crystal fields. 

The use of lasers for the excitation of Raman spectra of solids has led to the detection of many new elementary excitations of crystals and to the observation of nonlinear effects. In this review we have tried to lead the reader to a basic understanding of these elementary excitations or quasi-particles, namely, phonons, polaritons, plasmons, plasmaritons, Landau levels, and magnons. Particular emphasis was placed upon linear and stimulated Raman scattering at polaritons, because the authors are most familiar with this part of the field and because it facilitates understanding of the other quasi-particles. 

In thick ( 300 pm) crystals of GaN electronic excitons of shallow dopants have been observed in far infrared absorption at 215 cm 1 [44], Interpreted as the ls-2p transition of a residual shallow donor, its binding energy was calculated to be (35.5 0.5) meV. Further modes at 149 and 242 cm 1 have been observed in mixed phase GaN/GaAs in Raman scattering and have been associated with electronic excitations of shallow donors in cubic and sphalerite GaN, respectively [45] see also [46], Far infared absorption at 23.2 cm 1 in magnetic fields has been used to determine the effective electron mass in GaN, m = 0.20 0.005 m, (corrected for polaron effects) in cyclotron resonance [47]. 

As a result, several schemes including cavity-enhanced Raman [6], photonic crystal-enhanced Raman [7], surface-enhanced Raman [8], etc., have been put forward in an attempt to increase the electromagnetic field strength for excitation. Among them, surface-enhanced Raman scattering (SERS), by far, is one of... 

In the weakly anharmonic molecular crystal the natural modes of vibration are collective, with each internal vibrational state of the molecules forming a band of elementary excitations called vibrons, in order to distinguish them from low-frequency lattice vibrations known as phonons. Unlike isolated impurities in matrices, vibrons may be studied by Raman spectroscopy, which has lead to the establishment of a large body of data. We will briefly attempt to summarize some of the salient experimental and theoretical results as an introduction to some new developments in this field, which have mainly been incited by picosecond coherent techniques. 

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