Red luminescence band

For the red luminescence band, lifetimes of about 10 to 10 6 s are expected and the recombination is most probably phonon assisted. 

These exhibit green, blue, and red luminescent bands under UV irradiation, as a security measure. The red bands are doubtless due to some Eu + complex, probably with a /1-diketonate or some similar ligand. As we have seen, there are Eu + complexes that could cause the green and blue luminescence. Researchers at the University of Twente in the Netherlands suggest that a likely candidate for the source of the green colour is SrGa2S4 Eu +, and that the blue colour may be caused by (Ba0)j .6Al203 Eu +. It s quite appropriate that Euro notes contain europium, really. 

Coxon PR, Newman M, Hunt MRC, O Farrell N, Horrocks BR, Poolton NRJ, Siller L (2012) DNA-modified silieon nanocrystals studied by X-ray luminescence and X-ray absorption spectroscopies observation of a strong infra-red luminescence band. J Appl Phys 111 054311 Credo GM, Mason MD, Buratto SK (1999) External quantum efficiency of single porous silicon nanoparticles. Appl Phys Lett 74 1978-1980... 

Natural iron free enstatite exhibits mainly two orange-red luminescence bands peaking at 660 and 590 nm ascribed to Mn " centers substituting for Mg in different structural positions (Gorobets and Rogojine 2001). Luminescence bands peaking at 620-628 nm range have been found under 532 nm laser excitation (http //miff.info) (Fig. 4.174). 

Dependencies of luminescence bands (both fluorescence and phosphorescence), anisotropy of emission, and its lifetime on a frequency of excitation, when fluorescence is excited at the red edge of absorption spectrum. Panel a of Fig. 5 shows the fluorescence spectra at different excitations for the solutes with the 0-0 transitions close to vI vn, and vra frequencies. Spectral location of all shown fluorescence bands is different and stable in time of experiment and during lifetime of fluorescence (panel b)... 

The red PL band of PS can not only be excited by above bandgap photons, but also by an intense IR (1064 nm) pulse [Di6]. Such a thermostimulated luminescence is known for the case of glasses. This observation was attributed to PS having about 100 times the third-order nonlinear optical susceptibility of bulk Si, as discussed in Section 7.3. Multiphoton excitation of the red PL band by resonant pumping of the vibrational modes of surface groups like Si-O [Di4] or Si-H [Ch8] provided evidence for excitation modes that involve the porous skeleton surface. 

Microporous samples that have been illuminated in the electrolyte after anodization are found to exhibit a green or blue luminescence (peak energy from 2.1-3.0 eV) after drying in a vacuum or in an inert gas such as Ar. This PL red shifts within seconds to the common red PL-band if the PS is exposed to oxygen. This effect has been attributed to the formation of Si=Q double bonds,... 

Silica makes up 12.6 mass-% of the Earth s crust as crystalline and amorphous forms. It was found that both modifications show similar main luminescence bands, namely a blue one centered at 450 nm ascribed to which substitutes for Si, red centered at 650 nm linked with non-bridge O, and dark-red at 700-730 nm linked with Fe. Time-resolved luminescence of hydrous volcanic glasses with different colors and different Fe, Mn, and H2O contents were measured and interpreted (Zotov et al. 2002). The blue band with a short decay time of 40 ns was connected with T2( D)- Ai ( S) and Ai C G)- Ai ( S) ligand field transitions of Fe " ", the green band with a decay time of approximately 250 ps with a Ti( G)- Ai( S) transition in tetrahedrally coordinated Mn ", while the red band with a much longer decay time of several ms with T1 (4G)- Ai( S) transitions in tetrahedrally coordinated Fe ". We detected Fe " " in the time-resolved luminescence spectrum of black obsidian glass (Fig. 4.43d). 

Under powerful laser excitation with A = 532 nm manganese minerals, such as rhodonite and rhodochrosite, exhibit orange-red Ivuninescence even at room temperature. In rhodonite it is a band peaking at 620 nm with a halfwidth of 85-95 nm and a very long decay time of 5-6 ms (Fig. 4.67c,d). Such luminescence is typical for impurity Mn ". In rhodochrosite luminescence is more complicated. The luminescence band has a maximum near 640 nm and a half-width of 80 - 90 nm, which is typical for impurity Mn ", but a decay time of only 5-lOps is very short for such a center and indicates strong energy migration (Fig. 4.67a,b). 

Center Sn " belongs to the 5s configuration. As an impurity in artificial phosphors it is mainly responsible for narrow luminescence bands from the UV to the red part of the spectrum. Besides that intrinsic luminescence of tin compounds is also known (Donker et al. 1989). 

Copper in minerals luminescence is usually considered only as an effective quencher. Nevertheless, it is well known that a bright blue luminescence is emitted from Cu ions in inorganic solids by UV light irradiation. It was found that these materials have potential application to tunable lasers. For example, in Ca0-P20s glasses Cu is characterized by a luminescence band at 440 nm with a half-width of 100 nm and an excitation maximum at 260 nm. The decay time of luminescence is approximately 25 ps (Tanaka et al. 1994). Red fluorescence possibly connected with the Cu" pair is also known (Moine et al. 1991). 

In BaS04 Cu two bands are detected red and violet (Fig. 5.59). The red one peaking at 740 nm at room temperature has a half-width of 150 nm and decay time of 350 ps. The violet band peaking at 410 nm has at room temperature a half-width of 35 nm and decay time of 7 ps. At lower temperatures both bands disappear and the new IR one is detected. Such deep red luminescence in natural barite has been described earlier (Gaft et al. 1985) while the possible connection with Cu was not considered. 

The pH of deposition (adjusted by adding NH4OH, therefore pH increased but free Cd decreased) affected the PL spectra of the CdS films deposited from a standard solution [31]. A broad, red luminescence (ca. 1.2-2.0 eV with peak at 1.68 eV) was characteristic of all the spectra, regardless of deposition pH. At pH = 11.5, a narrow (0.18 eV half-width) green peak (2.255 eV) appeared, but it did not occur above or below this pH value). This peak, ca. 0.2 eV less than the bandgap, could be either a shallow-donor-to-shallow-acceptor transition or a band-to-fairly shallow interband state transition. 

Fig. 7.17. Optical properties of the (=Si-0)3Si-0 radicals, (a) The absorption bands at 2.0.and 4.9 eV and excitation spectrum of the red luminescence (b) the manifestation of the small Stokes shift for absorption band at 2eV.

The nature of the electronic transition related to the 4.9 eV absorption band (the C state) of oxy radical is still unknown. It was experimentally found [65] that the quantum yield of the red luminescence (1.95 eV) is equal to 0.5 + 0.2. Consequently, the nature of this excited state should be so that the transition to the B state will be possible with high probability from this state. This means that the terms corresponding to the C and B states are crossed or converged (come closer to each other) at any arbitrary point of the configurational space. 

The spectrum of the red luminescence has a complex stmcture. We were able to separate three components of red luminescence that each have their own kinetics and that differ by the character of excitation. The radiation band at 7300-7800 A is predominantly excited by light with A,i = 3700-4800 A and has a three - exponential time dependence of afterglow with time constants of 3 msec, 15 msec, and 75 msec. The relatively strong emission line at 7175 A has maxima in the excitation spectrum at 3700 and 5200 A. It is characterized by an afterglow time constant of x = 33 psec. Several narrow lines in the 6900-7200 A region are well excited with A,=4000-4800 A and are characterized by Xi = 3 and %2 = 22 msec. 

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