Green luminescence band

The details of the ground state of the Cuzn acceptor in ZnO have been established from the EPR and infrared absorption studies [107]. The low-temperature absorption spectrum of the Cu-doped ZnO contained two sharp lines at 717 and 722 meV. The details of the absorption spectra, the Zeeman splitting in magnetic field, and the EPR data allowed Dietz et al. [107] to construct the following model of Cuz in ZnO. The free ion term D of the Cu ion is split by the tetrahedral crystal field into the E (D) 

Dietz et al. [107] concluded that the Cu (2 wave function is radially expanded (more than e wave fimction) relative to the d wave function of the free Cu ion, and the t2 hole spends about 60% of its time on the Cu + ion, while it spends the rest of the time in the oxygen sp orbitals. The inverse E(D) — T2 (D) transition of the Cu ions in ZnO (a zero-phonon line at 717 meV) has been observed under electron-beam excitation at low temperatures [108]. 

Structureless GL band in ZnO was attributed also to Vzn acceptor [86,118-120], a complex defect involving Zn [121], Oz [122], and Vq [105,106,123-126]. Different authors suggested different types of electron transitions to explain the GL band, for example, from the Vo donor level located near the conduction hand to the valence band (D-h-type recombination) [105], from Vo or another donor level to deep Vzn acceptor level (DAP type) [119,120], from conduction hand to the Vz acceptor (e-A type) [86], and between two states of Vo (intracenter transition) [125]. However, as indicated earlier. Van de Walk [87, 88] predicted that V in ZnO has only the level (2+ /O) at about 2.2 eV above the valence hand. Note also that the D-h-type recomhi-nation is highly improbable in an n-type semiconductor [127]. Moreover, the DAP-type recombination observed in Ref. [120] may not be the same PL hand as others detected because its maximum is at 2.3 eV (shifting to 2.04eV after time delay), which is, in the yellow range. 

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In the solid state, the complexes exhibit a yellow-green luminescence under UV irradiation (365 nm). All the emission spectra are similar and consist of three broad emissions above 370 nm (e.g., 384, 490 and 524 nm for m = 10, w = 6), while the free isocyanides (white solids) are luminescent giving one strong emission band with its maximum at about 360 nm. In dicMoromethane solution both the free isocyanides and their gold complexes are luminescent too, but only one intense emission is observed for the complexes in the range of 345-387nm (Figure 8.14). The lifetime... 

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). 

Luminescence of Mn " is well known in the steady-state luminescence spectra of feldspars (Tarashchan 1978 Waychunas 1989 White 1990 GOtze 2000 Goro-bets and Rogojine 2001). Its green luminescence is predominantly detected in plagioclases. In K-feldspars the Mn " " emission is less common because of the difficulty of the Mn " - K" " substitution. Its band is also very well detected in laser-induced time-resolved spectra peaking at 550-560 nm (Eig. 4.43a). It is characterized by an extremely long decay time of 10-12 ms. 

Cerussite is characterized by several broad luminescence bands in the green-yellow part of the spectrum with different decay times (Fig. 5.52). Those bands are not confidently interpreted yet and only recently the idea of Ag or Cu participation has been proposed based on their close radii with Pb " (Gorobets and Rogojine 2001). We think that such interpretation is principally logical and has to be checked, but the possible participation of intrinsic lead also may be considered. 

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. 

Attention is drawn to the radiation-less character of the transition of electrons from the conduction band to the F -centers (a decrease in the concentration of the paramagnetic states F does not cause thermoluminescence, Fig. 6). This contradicts rather widespread models attributing the green luminescence of ZnO just to that sort of process. 

To characterize the optical properties of the rods obtained, the material was studied by means of PL spectroscopy. When excited with 240 nm uv radiation, the samples exhibit two bands centered at 394 and 486 nm, or, when converted to photon energy, 3.15 and 2.55 eV, respectively, and are due to oxygen vacancies [10]. The enhanced green luminescence from nanorods suggests their applicability in optoelectronic devices. 

The spectrum of the yellow-green luminescence due to combination of O with NO consists of an apparent continuum superimposed on which are reported to be a number of diifuse bands. The intensity maxima of these emission bands correspond well with those of the absorption bands of NO2 at 300 K. The high energy cut-off at 397 5 nm of the luminescence corresponds closely with the energy of the reaction. " ... 

Nitrogen. The reaction of PH3 in Ar with atomic N is accompanied by a pale green luminescence. The bands observed in the range 6000 to 2300 cm- were assigned to PH, PH2, PN, NJ, and NH. The final product is a solid [64]. The reaction of PH3 in the carrier gas He with N( S) atoms was found to be very slow. A rate constant of k 4.0 x10" cm molecule" s" at ambient temperature was determined in a flow tube by molecular-beam sampling mass spectrometry. This rate constant is compatible with the slight endothermicity (ArH298 = 4 kJ/mol) of the reaction PH3 + N- -PH2 + NH [36]. 

Finnic and coworkers identified the source of the green luminescence to be arsenic oxide microcrystals formed during porous-etching [211, 212] and that of the infrared band to the scattered excitation radiation, exciting luminescence from the relatively unperturbed outer regions of the etchpit [211]. 

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