Halide Phosphors

Alkali-Metal Halides. Luminescent alkali-metal halides can be produced easily in high-purity and as large single crystals. They are therefore often used as model substances for the investigation of luminescence processes. Their luminescence processes can be divided into 1) the self-luminescence of the undoped crystals, 2) luminescence by lattice defects, and 3) sensitized luminescence. 

Self-Luminescence. The action of UV light or ionizing radiation on pure alkali-metal halide crystals causes intense luminescence particularly at low temperature. The emission spectrum is characteristic for each individual compound. This fluorescence is comparable with the recombination luminescence which occurs upon capture of an electron by a VK center (defect electron). 

Luminescence of Lattice Defects. Many defect centers are known in the case of the alkali-metal halides, which are derived from electrons in anion vacancies (F-centers, or color centers). Association of two or more F-centers gives new defect centers, which can each also take up an electron. These lattice defects act as luminescence centers, the emission spectra of which sometimes exhibit a large number of lines. 

At certain temperatures phosphorescence can also be observed, which indicates strong relaxation in the excited state. 

Sensitized Luminescence. Through the incorporation of foreign ions (e.g., Tl+, Ga+, In+) into the crystal lattice, further luminescence centers are formed. The emission spectra are characteristic for the individual foreign ions. The complicated luminescence mechanism is described in [5.408]. 

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Alcohol Phosphorus trihalide Alkyl halide Phosphorous acid... 

The alkali-metal halide phosphors are produced by firing the corresponding alkali-metal halide and the activator in platinum or fused-silica crucibles under an inert atmosphere. 

Some industrially important alkali-metal halide phosphors are listed in Table 56. Nal. Tl and CsI. Tl are used as detectors for X and y rays because of their high... 

Alkaline-Earth Halides. Of the alkaline-earth halide phosphors, those doped with manganese or rare earths have been used industrially (Section 5.5.4.7) (e.g., CaF2 Mn CaF2 Dy). 

Other Halide Phosphors. Information on the most important manganese-activated phosphors is summarized in Table 57. 

The Tb halides are similar to the sdver hahdes in that they are sensitive to light. The yellow compound TII has a curious orthorhombic layer structure, which is transformed to a red metastable cubic form (CsCl type) at 4.7kbar or 175 °C, becoming a metallic conductor at about 160kbar. If a small quantity of a Tb halide is added to an aqueous solution of an alkali halide, a blue Luminescence is emitted furthermore, TlCl doped KCl behaves as a thalhum alkali halide phosphor. In both cases, TlCb is believed to be the active species. ... 

Solvents 25°C Dichloroacetic acid, trifluoroacetic acid, concentrated Li" " and NH halides, phosphoric acid (A 4)... 

A review on the TL of alkali-halide phosphors, including R-activated, ones was given by Sastiy (1993). 

Phosphorous acid is water soluble and may be removed by washing the alkyl halide with water or with dilute aqueous base... 

Amongst heat stabilisers are copper salts, phosphoric acid esters,phenyl-3-naphthylamine, mercaptobenzothiazole and mercaptobenzimidazole. Of these, copper salts in conjunction with halides have been found particularly effective, and some automotive specifications require the use of copper for heat stabilisation. Light stabilisers include carbon black and various phenolic materials. 

The Arbuzov reaction,also called the Michaelis-Arbuzov reaction, allows for the synthesis of pentavalent alkyl phosphoric acid esters 4 from trivalent phosphoric acid esters 1 (Z,Z = R,OR) by treatment with alkyl halides 2. 

The reaction mechanism outlined below for phosphorous acid esters analogously applies for the other two cases. The first step is the addition of the alkyl halide 2 to the phosphite 1 to give a phosphonium salt 3 ... 

In the phosphor-photoelectric detector used as just described, the x-ray quanta strike the phosphor at a rate so great that the quanta of visible light are never resolved they are integrated into a beam of visible light the intensity of which is measured by the multiplier phototube. In the scintillation counters usual in analytical chemistry, on the other hand, individual x-ray quanta can be absorbed by a single crystal highly transparent to light (for example, an alkali halide crystal with thallium as activator), and the resultant visible scintillations can produce an output pulse of electrons from the multiplier phototube. The pulses can be counted as were the pulses-from the proportional counter. 

These compds are also formed during the prepn of nitriles, by heating aryl or arylalkyl halides, or alkyl sulfuric or phosphoric esters, or arylsulfonic esters with K or Na cyanide in ale... 

Diesters of phosphorous acid are in general neutral because the phosphorous acid exists mostly in the phosphonate form with one hydrogen directly attached to the phosphorus. But with alkali metals the H can be changed against the alkali and reactive intermediates formed. Such alkali metal derivatives of dialkyl phosphites react with alkyl halides to give dialkyl alkanephosphonates, according to Eqs. (45) and (46). 

The important compounds of nitrogen with hydrogen are ammonia, Irydrazine, and hydrazoic acid, the parent of the shock-sensitive azides. Phosphine forms neutral solutions in water reaction of phosphorous halides with water produces oxoacids without change in oxidation number. 

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