Excitation luminescence and

A luminescent mineral is a sohd, which converts certain types of energy into electromagnetic radiation over and above thermal radiation. The electromagnetic radiation emitted by a luminescent mineral is usually in the visible range, but can also occur in the ultraviolet (UV) or infrared (IR) range. It is possible to excite the luminescence of minerals by UV and visible radiation (photoluminescence), by a beam of energetic electrons (cathodoluminescence), by X-rays (X-ray excited luminescence) and so on. A special case is so-called thermoluminescence, which is stimulation by the heating of luminescence, prehminary excited in a different way. 

Figure 11.10 Energy level diagrams for photoinduced electron transfer processed based on 11.8, showing excitation (--), luminescence (---) and nonradiative decay (—).

Figure 1 Simplified reaction scheme for dynamic and static luminescence quenching. L denotes the probe molecule in the electronically ground state, L is the excited luminescer, and Q is a quencher molecule.

In order to address the possible influence of positional disorder, we have chosen to analyze the way basic operations such as translations and rotations affect the properties calculated for highly symmetric configurations. This approach could provide guidelines to prevent the loss of significant optical coupling between the ground state and the lowest excited state, and hence the quenching of luminescence in the solid state. 

Therefore, there could exist rich defects in Ba3BP30i2, BaBPOs and Ba3BP07 powders. From the point of energy-band theory, these defects will create defect energy levels in the band gap. It can be suggested that the electrons and holes introduced by X-ray excitation in the host might be mobile and lead to transitions within the conduction band, acceptor levels, donor levels and valence band. Consequently, some X-ray-excited luminescence bands may come into being. 

The X-ray-excited Luminescence Properties of Ce -activated Ba3BP30i2, BaBPOs and Ba3BP07... 

Figures 21.16, 21.17 and 21.18 show the X-ray-excited luminescence properties of Ce -activated Ba3BP30i2, BaBPOs and Ba3BP07 respectively. They all show a broad emission band with peak center at about 351 nm for Ba3BP30i2 Ce, ...

Fig. 7. Excitation (a) and emission (b) spectra of the luminescence of La3Ta04Clg In at 4.2 K. After MJJ Lammers, thesis, Utrecht, 1986...

The method of exchange-luminescence [46, 47] is based on the phenomenon of energy transfer from the metastable levels of EEPs to the resonance levels of atoms and molecules of de-exciter. The EEP concentration in this case is evaluated by the intensity of de-exciter luminescence. This technique features sensitivity up to-10 particle/cm, but its application is limited by flow system having a high flow velocity, with which the counterdiffusion phenomenon may be neglected. Moreover, this technique permits EEP concentration to be estimated only at a fixed point of the setup, a factor that interferes much with the survey of heterogeneous processes associated with taking measurements of EEP spatial distribution. 

Pelletier and Reber315 present new luminescence and low-energy excitation spectra of Pd(SCN)42 in three different crystalline environments, K2Pd(SCN)4, [K(18-crown-6)]2Pd(SCN)4, and (2-diethylammonium A -(2,6-dimethylphcnyl)acetamide)2Pd(SCN)4, and analyze the vibronic structure of the luminescence spectra, their intensities, and lifetimes as a function of temperature. The spectroscopic results are compared to the HOMO and LUMO orbitals obtained from density functional calculations to qualitatively illustrate the importance of the bending modes in the vibronic structure of the luminescence spectra. 

The areas where the use of the track model has been found particularly expedient are (1) LET variation of product yields in the radiation chemistry of liquids (2) the yield of escaped ions and its variation with particle LET (3) energy loss in primary excitations and ionizations (4) radiation-induced luminescence and (5) particle identification. 

Excited states may be formed by (1) light absorption (photolysis) (2) direct excitation by the impact of charged particles (3) ion neutralization (4) dissociation from ionized or superexcited states and (5) energy transfer. Some of these have been alluded to in Sect. 3.2. Other mechanisms include thermal processes (flames) and chemical reaction (chemiluminescence). It is instructive to consider some of the processes generating excited states and their inverses. Figure 4.3 illustrates this following Brocklehurst (1970) luminescence (l— 2)... 

Nelly R.N., Schulman S.G., Proton-Transfer Kinetics of Electronically Excited Acids and Bases, in Molecular Luminescence Spectroscopy Methods and Applications, part 2, Schulman S.G. (ed.), Wiley-Interscience, New York, 1988 pp 461-510. 

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