Ultra-violet emission

Typical luminescence spectra of as-grown crystals show ultra-violet emission due to free excitons (including their longitudinal optical phonons-EO replicas) as well as t5 ical bands of green and yellow-orange luminescence (the temperature is 77-80 K). When the temperature is 4.2 K, the luminescence of bound excitons (including their LO - replicas) dominates. ... 

Under excitation of a 980 nm laser diode, a dazzling green spot from both samples could be clearly seen by the naked eye. Figure 3 gives the typical upconversion luminescent emission bands. Green and near-infrared emission bands were detected in both samples, which were very similar to fluorescent emissions. Especially, the red emission band was measured around 667 nm associated with the F5—> lg transition. Furthermore, the ultra-violet and blue upconversion emissions can also be measured. The ultra-violet emissions in the ranges of 381-394 nm and 409-428 nm are assigned to the G4—> lg and G5— Ig transitions, respectively. The blue emission between 473 and 500 nm... 

Spectroscopic techniques look at the way photons of light are absorbed quantum mechanically. X-ray photons excite inner-shell electrons, ultra-violet and visible-light photons excite outer-shell (valence) electrons. Infrared photons are less energetic, and induce bond vibrations. Microwaves are less energetic still, and induce molecular rotation. Spectroscopic selection rules are analysed from within the context of optical transitions, including charge-transfer interactions The absorbed photon may be subsequently emitted through one of several different pathways, such as fluorescence or phosphorescence. Other photon emission processes, such as incandescence, are also discussed. 

The quantized nature of electronic energy levels due to size confinement is amplified in this term. They show characteristic absorption features and can be distinguished from each other from their absorption profiles [2], Quantum clusters typically exhibit strong photoluminescence and their wavelength of emission can be tuned from the near infra red (NIR) to ultra violet (UV) [1]. 

The work function of electrodes emersed from aqueous solutions in ultra high vacuum (UHV) can be measured by means of the ultra-violet photo-electron emission spectroscopy (UPS) [KOtz-Neff-MUller, 1986]. Figure 4-27 shows the work function measured by UPS of the emersed metal electrodes of gold,... 

The characteristic absorption and emission spectra of lanthanide compounds in the visible, near ultra-violet and infra-red is attributed to transitions between 4/ levels due to the fact that they present a sharp line with oscillators strengths typically of the order of 10 . These transitions are electric dipole forbidden but became allowed as forced electric dipole transitions. 

Ultra-violet X-ray excited luminescence of Pr was first observed in minerals in anhydrite, but have been mistakenly ascribed to transitions from Ijj2 and Ds/2 levels in Gd " (Gaft et al. 1985). According to CL spectra of anhydrite artificially acfivated by Pr " " (Baumer ef al. 1997 Blank ef al. 2000) the emission lines at 228, 239, 258 and 268 nm (Fig. 4.17a) belong to Pr " and may be connected with Sq and Sq -> 64 transitions. The lines... 

The photoelectric effect has received its simplest explanation in terms of the electron theory in which the phenomenon is attributed to the emission of electrons under the influence of ultra-violet light. J. J. Thomson 8 proved that the carriers of negative electricity from an illuminated metal plate are identical with the cathode rays of a Crookes tube, and consist of negatively electrified corpuscles or negative electrons carrying an electrical charge equal to that concerned in electrolytic... 

Three kinds of phenomenon play their part in the production of these band spectra, electronic changes within the molecule, vibration of the atoms in the molecule, and rotation of the molecule as a whole. The electronic processes give rise to emission or absorption in the visible and ultra-violet regions, the intra-atomic vibrations to bands in the short infra-red region at wave-lengths of the order of several /x, and the molecular rotations to bands in the far infra-red at wave-lengths of the order 100 /. ... 

A. Schuster 8 found that the spectrum of ammonia in the discharge tube shows a broad, greenish-yellow band between 5688 and 5627. G. Magnanini observed the spectrum of the flame of ammonia burning in oxygen exhibits a large number of hydrogen lines. This spectrum was also observed by J. M. Eder, who measured 240 lines between A=5000 and 2262 for the extreme ultra-violet. The emission spectrum has seven characteristic bands—one between the red and ultra-violet. 

The electron affinity can also be deduced from the measurement of the spectrum of the photoelectron emission with monochromatic UV light. This technique is ultra-violet (UV) photoelectron emission spectroscopy (or UV photoemission spectroscopy or UPS). The UPS technique involves directing monochromatic UV light to the sample to excite electrons from the valence band into the conduction band of the semiconductor. Since the process occurs near the surface, electrons excited above the vacuum level can be emitted into vacuum. The energy analysis of the photoemitted electrons is the photoemission spectrum. The process is often described in terms of a three step model [8], The first step is the photoexcitation of the valence band electrons into the conduction band, the second step is the transmission to the surface and the third step is the electron emission at the surface. The technique of UPS is probably most often employed to examine the electronic states near the valence band minimum. 

The narrow absorption and emission bands of rare-earth 0-diketonates in the visible, near ultra-violet and near infra-red is attributed to 4f-4f transitions. These transitions are electric dipole forbidden to first order, but are allowed by the electric quadrupole, vibronic, magnetic dipole and forced electric dipole mechanisms. The magnetic dipole character of the Dq F transition of the Eu + ion was demonstrated in 1939 by... 

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