Luminescent Minerals

At the second level, the type of chemical compounds subdivides luminescent minerals homoatomic compounds, sulfides, halides and oxygen-bearing compounds. Such level is mainly important for recombination induced liuni-nescence and practically is not considered in our book. 

At the third level, the most detailed partition of luminescence minerals is carried out on the basis of metals in the mineral formulae, hi rare cases we have minerals with host luminescence, such as uranyl minerals, Mn minerals, scheelite, powellite, cassiterite and chlorargyrite. Much more often luminescent elements are present as impurities substituting intrinsic cations if their radii and charges are close enough. Thus, for example, Mn + substitutes for Ca and Mg in many calcium and magnesium minerals, REE + and REE substitutes for Ca, Cr substitutes for AP+ in oxygen octahedra, Ee substitutes for Si in tetrahedra and so on. Luminescence centers presently known in solid-state spectroscopy are summarized in Table 4.2 and their potential substitutions in positions of intrinsic cations in minerals in Table 4.3. 

for a mineral to be luminescent the following three conditions must be satisfied at once (1) a suitable type of crystal lattice favorable to forming emission centers (2) sufficient content of luminescence centers and (3) a small amount of quenchers. We arrange the luminescent minerals in our book according to the main major element, the substitution of which by luminescence centers determines the emission properties of a mineral. 

Besides luminescence properties, we also added the short data on color of corresponding minerals, because, as was already mentioned, such information is often useful for an imderstanding of liuninescence nature. The data on ionic radii of different elements and the main structural data are taken from corresponding Internet sites. 

The Eigures contains the following symbols [a.u. ] - arbitrary units, D-delay, G-gate. 

Gaft et al., Modern Luminescence Spectroscopy of Minerals and Materials, 

I - Partition into four types of chemical bounding 

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A luminescent mineral is a sohd, which converts certain types of energy into electromagnetic radiation over and above thermal radiation. The electromagnetic radiation emitted by a luminescent mineral is usually in the visible range, but can also occur in the ultraviolet (UV) or infrared (IR) range. It is possible to excite the luminescence of minerals by UV and visible radiation (photoluminescence), by a beam of energetic electrons (cathodoluminescence), by X-rays (X-ray excited luminescence) and so on. A special case is so-called thermoluminescence, which is stimulation by the heating of luminescence, prehminary excited in a different way. 

The luminescent mineral consists of a host lattice and a luminescent center, often called an activator. The determination of the nature of the center responsible for luminescence is not generally a trivial task. Correlation of the observation of the specific luminescence with a particular impurity concentration may give an indication of the source of the emission but it is not proof of the origin, and can sometimes be misleading. Furthermore, it does not give any details about the precise nature of the center. Spectroscopic studies may... 

At the same time, solid-state physicists intensively dealt with synthetic analogues of luminescent minerals as phosphors and quantum electronic materials, providing the theoretical and experimental background for further applications in high technology material sciences. These achievements are shortly summarized in Table 1.2. 

With small dimensions of the forbidden band the electron transfer of the impurity or of the main substance to the conduction band may take place. The most important luminescent minerals of this kind are ZnS and silver bromides. With the interband spacing of 3-4 eV a UV irradiation with a wavelength of less than 300 nm has enough energy to detach electrons and transfer them from the filled valence band into an empty conduction... 

Identification of minerals is not a trivial question when dealing with natural objects. Luminescent minerals received from different mineralogists, museums and collectors are often not correctly identified. It is a potential source of serious errors, because the presence of a certain luminescence center in one mineral maybe trivial, while its luminescence in another mineral may represent a certain interest. For example, emission of Mn " is common in calcite, but its absence in scheelite is an interesting problem. Thus, when you find the band... 

The Introduction chapter contains the basic definitions of the main scientific terms, such as 5pectro5copy, luminescence spectroscopy, luminescent mineral, luminescent center, luminescence lifetime, luminescence spectrum and excitation spectrum. The state of the art in the steady-state luminescence of minerals field is presented. The main advantages of the laser-induced time resolved technique in comparison with the steady-state one are shortly described. 

The Luminescent Minerals chapter contains time-resolved luminescence spectra for approximately 50 minerals. The following information is presented for the each one, comprising literature and original results short description... 

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