Luminescence energy levels

The triplet-state energy level of oxytetracycline, the excitation maximum (412 nm), lifetimes of Eu-OxTc (58 p.s) and Eu-OxTc-Cit (158 p.s), were determined. A 25-fold luminescence enhancement at 615 nm occurs upon addition of citrate within a short 5-min incubation time at neutral pH. It s accompanied by a threefold increase of the luminescence decay time. The optimal conditions for determination of OxTc are equal concentrations of Eu(III) and citrate (C = T lO mol-E ), pH 7.2. Eor determination of citrate, the optimal conditions concentrations of Eu(HI) and OxTc are 1 0,5 (Cg = MO Huol-E-i, = 5-10-HuohE-i) at pH 7.2. 

Jablonski (48-49) developed a theory in 1935 in which he presented the now standard Jablonski diagram" of singlet and triplet state energy levels that is used to explain excitation and emission processes in luminescence. He also related the fluorescence lifetimes of the perpendicular and parallel polarization components of emission to the fluorophore emission lifetime and rate of rotation. In the same year, Szymanowski (50) measured apparent lifetimes for the perpendicular and parallel polarization components of fluorescein in viscous solutions with a phase fluorometer. It was shown later by Spencer and Weber (51) that phase shift methods do not give correct values for polarized lifetimes because the theory does not include the dependence on modulation frequency. 

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 trinudear complex [Au3(p-triphos)(QF5)3] [97] in dichloromethane shows an absorption around 270 nm and in the solid state at room temperature the complex does not emit, even using an excitation frequency below 300 nm. At lower temperature (77 K) the complex emits with a maximum at 450 nm. Thus luminescence properties can be dramatically influenced by the pentafluorophenyl group which indicates its important contribution to the energy levels involved in the electronic transitions. 

Figure 3 Energy level diagram for selected luminescent lanthanide ions.

Arnaud, N., and Georges, J. (2003) Comprehensive study of the luminescent properties and lifetimes of Eu(3 + ) and Tb(3 + ) chelated with various ligands in aqueous solutions Influence of the synergic agent, the surfactant and the energy level of the ligand triplet. Spectrochim. Acta A Mol. Biomol. Spectrosc. 59(8), 1829-1840. 

In 1935, after studying the luminescence of various colorants, Jablonski suggested the electronic energy diagram of the singlet and triplet states to explain the luminescence processes of excitation and emission. The proposed diagram of molecular electronic energy levels formed the basis of the theoretical interpretation of all luminescent phenomena [21],... 

Figure 9.24 Energy-level diagram for a luminescent species, in which a metastable state slows the rate of emission. The metastable state is also termed an ion trap...

Abstract Silver clusters, composed of only a few silver atoms, have remarkable optical properties based on electronic transitions between quantized energy levels. They have large absorption coefficients and fluorescence quantum yields, in common with conventional fluorescent markers. But importantly, silver clusters have an attractive set of features, including subnanometer size, nontoxicity and photostability, which makes them competitive as fluorescent markers compared with organic dye molecules and semiconductor quantum dots. In this chapter, we review the synthesis and properties of fluorescent silver clusters, and their application as bio-labels and molecular sensors. Silver clusters may have a bright future as luminescent probes for labeling and sensing applications. 

Two principal ways exist to use a dye as a sensor of local polarity (or of microscopic electric fields) (1) monitoring the polarity-induced shift of the energy levels, e.g., the red shift of the fluorescence and (2) monitoring changes in fluorescence intensity induced by the polarity- or field-induced modulation of nonradiative rates. As these compete with the fluorescence emission, the fluorescence intensity (and lifetime) is correspondingly modulated. (3) In some cases, the radiative rates are also solvent sensitive this is usually connected with the formation of luminescent products. 

Figure 1.9 The energy-level and transition schemes and possible luminescence spectra of a three-level ideal phosphor (a) the absorption spectrum (b, c) emission spectra under excitation with light of photon energies hvi and /iV2, respectively (d, e) Excitation spectra monitoring emission energies at /i( V2 — vi) and at /i vi, respectively. Arrows mark the absorption/emission transitions involved in each spectrum. Eixed indicates that the excitation or emission monochromator is fixed at the energy (wavelength) corresponding to this transition.

Figure 1.11 An example of a four energy level system producing anti-Stokes luminescence.

Once a center has been excited we know that, in addition to luminescence, there is the possibility of nonradiative de-excitation that is, a process in which the center can reach its ground state by a mechanism other than the emission of photons. We will now discuss the main processes that compete with direct radiative de-excitation from an excited energy level. 

Figure 5.22 Schemes of possible mechanisms for luminescence concentration quenching (a) energy migration of the excitation along a chain of donors (circles) and a killer (black circle), acting as nonradiative sink (b) cross relaxation (including an illustrative energy-level diagram) between pairs of centers. (Sinusoidal arrows indicate nonradiative decay or radiative decay from another excited level.)...

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