Halides luminescent materials

Lighting. An important application of clear fused quartz is as envelop material for mercury vapor lamps (228). In addition to resistance to deformation at operating temperatures and pressures, fused quartz offers ultraviolet transmission to permit color correction. Color is corrected by coating the inside of the outer envelope of the mercury vapor lamp with phosphor (see LUMINESCENT MATERIALS). Ultraviolet light from the arc passes through the fused quartz envelope and excites the phosphor, producing a color nearer the red end of the spectrum (229). A more recent improvement is the incorporation of metal halides in the lamp (230,231). 

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]. 

Some other polymers of the same type with valence (I) were also prepared (Fig. 17). They exhibit almost the same structure, except that halides are replaced by diphosphine ligands (diphos) such as bis(diphenylphosphino) butane (dppb), bis(diphenylphosphino)pentane (dpppen), and bis(diphenyl-phosphino)hexane (dpph).36,40 Again a model complex, compound 25, was studied as reference (Fig. 17). The electronic spectra exhibit an absorption band near 480 nm. These coordination materials are not luminescent at room temperature but are luminescent in solution in butyronitrile at low temperature (i.e., 77 K). Density functional theory (DFT) calculations showed that luminescence arises from a da-da triplet excited state. In these polymers, the nature of the phosphine ligand has a crucial effect on absorption and emission bands. Such behavior is explained by the increase in electronic density on the... 

Halides can form colour centres with absorption bands in the visible range. Doped with europium whose decay time of the allowed 5d —< 4f transition is of the order of 1 fis, they are the most appropriate materials. Because of the presence of fluorine, only BaCIF Eu and BaBrF Eu have a high enough chemical stability for screens fabrication. The highest efficiencies of photostimulated luminescence have been obtained with the fluorobromide (Amax = 390 nm). 

If Tl -activated alkali halides ate desired, thallium iodide has to be mixed with the starting material (Nal or Csl) and dissolved in the melt. The distribution coefficient of thallium in the alkali halide was measured to be about 0.2 for Nal [16] and 0.1 for Csl [17], using the ratio Tl concentration in the ctystal/TI concentration in the melt. During crystal growth the concentration of thallium in the melt will increase, but since thallium is volatile at the melting point of Nal (T 652°C) and Csl (T 623 C), some of the thallium may be lost by evaporation. This means that the TI+ concentration in a given ciystal will not be constant over the ciystal volume. Fortunately the luminescence intensity is nearly constant for Tl concentrations in Nal between 0.02 -0.2 mol per cent [16] and in Csl between 0.06-0.3 mol per cent... 

Near-Infrared Materials Luminescent Bioprobes Lanthanides in Living Systems Lanthanide Halides. 

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