Phosphors, alkali halide

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. ... 

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

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. 

Chapter 6 is devoted to discussing the main optical properties of transition metal ions (3d" outer electronic configuration), trivalent rare earth ions (4f 5s 5p outer electronic configuration), and color centers, based on the concepts introduced in Chapter 5. These are the usual centers in solid state lasers and in various phosphors. In addition, these centers are very interesting from a didactic viewpoint. We introduce the Tanabe-Sugano and Dieke diagrams and their application to the interpretation of the main spectral features of transition metal ion and trivalent rare earth ion spectra, respectively. Color centers are also introduced in this chapter, special attention being devoted to the spectra of the simplest F centers in alkali halides. 

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... 

The material is thermally stable up to 900°C and inert in most chemical reagents. Talc is practically insoluble in water, dilute mineral acids, and dilute solutions of alkali halides [6] and alkaline hydroxides [4]. It is soluble in hot concentrated phosphoric acid [3],... 

However, detailed insights into the electronic transitions of lead-thiolate complexes can be gained from studies on T1(I) [which is isoelectronic with Pb(ll)] and Pb(ll)-doped alkali halides in the solid state (Fig. 5) (37, 50, 54, 113). The details of the electronic transitions in T1(I) doped alkali halides and related compounds have been studied extensively (both theoretically and experimentally) because these compounds have interesting luminescent properties and are useful in phosphors. [We will not discuss the emission spectra of these compounds, as they are not relevant to our discussion of lead-thiolate CT in coordination complexes rather, the reader is directed to several extensive reviews of luminescence in doped alkali halide systems (95, 113, 114).] The characteristic absorption spectra of alkali halides doped with a Tl(l) type ion consist of four bands, known as the A, B, C, and D bands. The A band is at lowest energy, followed by B, C, and D respectively the extinction coefficients of the bands follow the general trend D > C > A > B (Fig. 6) (115, 116). Two weaker bands labeled D and D" are also shown in Fig. 6, which are attributed to the same CT transitions as the main D band (116). In Section II.E, we will... 

The alkali halides doped with heavy metal ions constitute one of the most thoroughly studied classes of phosphors. The following discussion of the effect of pressure on the absorption spectra will be confined largely to the T1+ ion with a few remarks concerning other ions. 

Mercuric cyanide, which ionizes in solution only to a minute degree, remains unaltered if its solution is treated with dilute nitric, sulfuric, phosphoric or oxalic acid even after prolonged heating. In contrast, dilute hydrochloric acid leads to the inunediate release of hydrogen cyanide. The same holds true when alkali halides are added to a solution of mercuric cyanide that has been acidified with sulfuric acid etc. Hence the underl3ung reaction, with participation of halogen ions, may be ... 

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 distillation is continued till the greater part of the liquid has distilled over, and no oily drops are to be seen in the condenser. The residue consisting of a concentrated solution of phosphorus and phosphoric acids in addition to excess of red phosphorus is discarded. The distillate is shaken up with water to remove alcohol, and then with dilute caustic soda to remove free iodine. Enough alkali must be used to render the lower layer of alkyl halide colourless. The latter is then separated ofl, dried over granular calcium chloride (6 gms.) and distilled. The preparation should be kept in the dark in a well-stoppered bottle. If exposed to light, iodine slowly separates, but may be prevented from so doing by adding a small quantity of colloidal silver to the liquid. 

Effluents from the manufacture of Pb(CH3)4 can be treated with an alkali metal borohydride, e.g., NaBH4 at pH 8 to 11 to substantially reduce the level of dissolved lead compounds, like [Pb(CH3)3][145, 146]. Zn can also be used [147]. Liquid NH3 and toluene are used to remove solid NH4Clfrom the apparatus for producing Pb(CH3)4 by the NH3- or amine-catalyzed reaction of CH3CI with a PbNa alloy [148]. Stabilization of Pb(CH3)4, and of antiknock fluids containing Pb(CH3)4, is accomplished by addition of compounds, like toluene [149], xylene [141, 150], styrenes [151], naphthalenes [149, 151, 152], anthracenes [152], substituted phenols [141, 152 to 155], olefinic hydrocarbons [152], alcohols [141, 152], amines [155], hydroquinones [156], ethers [141], saturated or unsaturated carboxylic acids [141, 152], esters of phosphoric acid [152], or of sulfuric acid [157], or of sulfonic acids [141], imidazoles [158], alkyl halides and alkyl thiocyanates [141], or tall oil [159] see also Organolead Compounds , Vol. 2, Section 1.1.1.2, to be published. 

---