Luminescence from crystals

Examples include luminescence from anthracene crystals subjected to alternating electric current (159), luminescence from electron recombination with the carbazole free radical produced by photolysis of potassium carba2ole in a fro2en glass matrix (160), reactions of free radicals with solvated electrons (155), and reduction of mtheiiium(III)tris(bipyridyl) with the hydrated electron (161). Other examples include the oxidation of aromatic radical anions with such oxidants as chlorine or ben2oyl peroxide (162,163), and the reduction of 9,10-dichloro-9,10-diphenyl-9,10-dihydroanthracene with the 9,10-diphenylanthracene radical anion (162,164). Many other examples of electron-transfer chemiluminescence have been reported (156,165). 

Image plates use stimulated luminescence from storage phosphor materials. The commercially available plates are composed of extremely fine crystals of BaFBrEu2+. X-rays excite an electron of Eu2+ into the conduction band, where it is trapped in an F-center of the barium halide with a subsequent oxidation of Eu2+ to Eu3+. By exposing the BaFBrEu" complex to light from a HeNe laser the electrons are liberated with the emission of a photon at 390 nm [38]. 

Observations of the decay time of luminescence from activator atoms in crystals excited by laser pulses have enabled lifetimes of... 

The 4f-> 5d transitions of nearly all Ln + ions have been observed in CaF2 (9). Luminescence from these transitions has been studied in detail for Eu2+ 10), Sm + (77) and Yh + (12). In good approximation these spectra can be ascribed as transitions between the 4/ ground state and the d crystal-field components of the state. The influence of the surroundings on these transi-... 

Firstly we shall consider the various forms of conventionally determined spectra, as distinct from time-resolved spectra, which can be obtained using continuous excitation. The measurement of emission spectra enables parameters such as the spectral position, spectral width, and spectral intensity to be determined. Moreover, the variation of these parameters with temperature is very important in deciding the origin of spectral bands. Sometimes the luminescence from single crystals is polarized and this can also give information as to the nature of the center. 

CD ZnSe has also been demonstrated to passivate surface states, 0.92 eV below the conduction band edge (measured by thermally stimulated exoelectron emission) on single crystal GaAs. This passivation resulted in bandgap luminescence from the originally non-luminescent GaAs [49a]. 

Shavaleev, N.M., Accorsi, G, Virgili, D., etal. (2005) Syntheses and crystal structures of dinuclear complexes containing d-block and f-block luminophores. Sensitization of NIR luminescence from Yb(III), Nd(III), and Er(III) centers by energy transfer from Re(I)- and Pt(II)-bipyrimidine metal centers. Inorganic Chemistry, 44, 61. 

There is a strong need for more detailed experiments. on well-chosen and characterized compounds. In the first place low-temperature polarization measurements on single crystals of e.g, YVO4 or CaMoO4 could inform us further on the splitting of the T, level. It seems worth while to search for luminescence from the tetrahedral CrO complex, especially because advanced calculations on this complex are availa-... 

Van Deun et al. were the first to observe near-infrared luminescence from lanthanide-doped liquid crystal mixtures They studied the spectroscopic properties of the lanthanide(III) / -diketonate complexes [L (dbm)3(phen)], where Ln = neodymium, erbium, ytterbium, and dbm is dibenzoylmethane, in the liquid crystal MBBA. By incorporation of an erbium(III)-doped nematic liquid crystal (ErCls dissolved in E7) in the pores of microporous silicon, narrowing of the erbium(III) emission band in the near-infrared was observedJ Luminescent optically active liquid crystals were obtained by doping [Eu(tta)3-3H20] into a mixture of cho-lesteryl nonanoate, cholesteryl tetradecanoate and the ternary liquid crystal mixture ZLI1083 from MerckJ ... 

The project Carl gave me was to build a sensitive instrument to search for luminescence from the permanganate ion, which had been the subject of a series of experimental single crystal absorption spectral studies and theoretical studies in the laboratory [6]. The spectrometer was built, but after repeated attempts using a range of crystals, excitation conditions and temperatures, no luminescence was detected. All subsequent efforts by others have confirmed this failure [7], under laser irradiation in iodide lattices some emission has been detected, but this is derived from the manganese ion MnO, 2 produced by a photoredox process [8]. This left me without many results to show for my year s work. I made some measurements on the intensely luminescent alkali metal platinocyanides but this did not lead to any new insights. 

Phosphorescence Spectra.—Luminescence from a low-lying triplet state of water368 has been reported. It has been shown that two long-lived emission systems in the biacetyl crystal described previously by Sidman and McClure (see ref. 368) are in fact due to impurities, and a complete analysis is presented of the true 3AU xAg phosphorescence. The zero-zero band in emission is found at 20 327 cm-1.135 A satisfactory account of the six characteristic bands in the phosphorescence spectrum of benzene has been given on the basis of pseudo-Jahn-Teller vibronic interactions between the lower 3Blu and 3Elu states in which two active vibrations in the pseudo-cylindrical approximation are considered.369 The phosphorescence spectra of anthracene,3700 coronene,8706 benzophenone in aqueous solution,371 pyrimidine derivatives,372 porphyrins,298 873 and crystalline charge-transfer complexes 374 have been reported. 

The other states which may arise from simple orbital promotions may be depicted by introducing a set of five non-degenerate d-orbitals. The lowest three of these stem from the degenerate Ug set in octahedral symmetry, and these three contain the six paired d-electrons of Ir(III). Crystal field or d-d excited states of the complex arise from promotion of electrons from these filled d-orbitals to the two empty ones which stem from the eg set in octahedral symmetry. Since no luminescence from a d-d excited level has been observed in the complexes we are considering, all of the d-d excited states are presumably at a higher energy than the TTTT and dir states. Charge-transfer or states arise from promotion of an electron from the filled d-orbitals to the tt complex orbitals. 

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