Lattice mercury compounds

For Hg, the value is based on the structure of Hgp2, one of the few mercury compounds with a typical ionic lattice. 

The alkali metal-graphite compounds are extremely reactive. They ignite in air and may react explosively with water. In the controlled reaction with water or alcohol only alkali hydroxide and hydrogen result there is no acetylene or any other hydrocarbon. Fredenhagen concluded from this that the compounds could not be carbides. Mercury dissolves the alkali metal out of the lattice. When treated with liquid ammonia, CgMe gives up only a third of the alkali metal and takes in its place two molecules of ammonia (see Section IIIA4). 

The structure of Hg. BnAsFe can he described as octahedral AsFe" ions arranged on a lattice that contains linear nonintersecting channels in two mutually perpendicular directions. Within these channels are infinite chains of mercury atoms, each with a fractional formal charge of +0.35 and a mercury-mercury distance of 2.64(1) A. Conductivity experiments confirm the metallic nature of the compound. The resistivity, measured by a four-probe ac technique, decreases by a factor of 10 between room temperature and 4.2°K. No metal-insulator transition was detected. 

A problem with this phosphor is that without precautions it usually contains a small amount of unreacted V2O5 which lowers the light output. For application in high-pressure mercury vapor lamps this pho.sphor is usually prepared with an excess of boric acid. The material has then a white body color and, in addition, the particle size can be controlled. The boron is not built into the lattice in some way or another the boron compound acts as a flux. 

The PL and TL of Zn compounds, especially ZnS, has been studied extensively. Very little was published, however, on R-activated Zn compounds. Anderson et al. (1965) worked on the PL of Tb-, Nd-, Tm- and Dy-doped ZnS. They found a strong tendency of the R ions to pair with other lattice defects in the presence of excess S. At least four distinct sites were observed for the R ions in the ZnS lattice. Tripathi et al. (1980) studied the TL of doubly doped ZnS Tb,Cu and ZnS Tb,Ag. The phosphor powders were fired for 40 min at 1020 C. The TL was studied up to 420 K and the main peaks above RT appeared near 300 K for the Tb,Cu activators and at about 310-320 K for the silver codoping. The trap depths for the main peaks were about 0.6 eV Tripathi et al. (1991) worked on the TL of ZnS Dy and ZnS Dy,Mn excited by 365 nm mercury light. The GCs above RT exhibited maxima at about 310-320 K. Trap depths E calculated for the main peaks were... 

In comparison with the acid digestion method, the hydrogenation method is more susceptible to matrix interferences. Two types of interferences are possible. Samples containing zinc, cadmium or mercury cannot be analyzed, as the high volatility of these elements results in the formation of a metallic mirror on the cooler parts of the tubing, which partially or completely absorbs the released sulphide. Sulphur may also be retained in the sample because it is present in the form of sulphur compounds which are not reduced or decomposed, e.g. manganese sulphide, or is held in crystal lattices which do not allow sufficiently rapid diffusion of sulphur at the temperature of 1150°C. 

Wessels AL, Czekalla R, Jeitschko W (1998) Structiffe of the mercury(II) chromate(III) HgCr204 and lattice constants of isotypic mercury(I) compounds Hg2Mo04 and Hg2W04. Mater Res Bull 33 95-101... 

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