Mineral luminescence

Table 1.1. Minerals luminescent under UV lamp excitation ...

In most luminescence experiments, at least in the mineral luminescence field, excitation is due to absorption of a single photon. However, it is also possible for a luminescence center to absorb two or more long-wavelength photons to reach the excited state. Two-photon excitation occurs by the simultaneous absorption of two lower-energy photons. Such excitation requires special conditions including high local intensities, which can only be obtained from laser sources. 

The possibility of Ni participation in minerals luminescence has not been seriously considered yet, but we are confident that it has to be done. The ionic radius of Ni " is 69 pm in tetrahedral coordination and 83 pm in the octahedral one. Thus it may substitute many cations with similar dimensions, such as Mg, Zn, Ca. 

It was originally stated that CaCOa activated with manganese cannot be excited by UV radiation, but CaCOa activated with lead, thallium or cerium and manganese shows an orange-red manganese luminescence under UV irradiation at room temperature (Bolden 1952). Nevertheless, in many minerals luminescence of Mn " " has been found with excitation spectra typical for this center without additional bands of Pb or Ce impurities. 

Copper in minerals luminescence is usually considered only as an effective quencher. Nevertheless, it is well known that a bright blue luminescence is emitted from Cu ions in inorganic solids by UV light irradiation. It was found that these materials have potential application to tunable lasers. For example, in Ca0-P20s glasses Cu is characterized by a luminescence band at 440 nm with a half-width of 100 nm and an excitation maximum at 260 nm. The decay time of luminescence is approximately 25 ps (Tanaka et al. 1994). Red fluorescence possibly connected with the Cu" pair is also known (Moine et al. 1991). 

Luminescence information on transition elements is substantially improved. Besides well known Mn + centers, emission of Mn was found and Mn + proposed as a possible participant in minerals luminescence. Luminescence characteristics of Mn +, Cr +, Ti +, Ni, Sb are presented and their... 

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. 

Besides confidently identified centers, the possible participation of Mn and is proposed. The centers, such as Mn ", Cr, Cr +, and V are described, which are not found in minerals yet, but are known in synthetic analogs of minerals, such as apatite, barite, zircon and corundum. Besides that, the centers Ni " and Ti " are discussed as possible participants in mineral luminescence. The last part of this chapter is devoted to unidentified emission lines and bands in apatite, barite, calcite and zircon. 

Our special thanks for Arnold Marfunin, Arkadii Tarashchan and Boris Gorobets for great contribution in minerals luminescence research. 

This paper reviews briefly the mechanisms responsible for mineral luminescence, then turns to less common modes of excitation, particularly ion and radical recombination luminescence, and finally discusses luminescence on the scale of remote sensing of planetary surfaces. 

The literature on mineral luminescence is somewhat bimodal in character. On one hand those mineral structures that have proved useful as phosphors or as crystal lasers have been studied in great detail and the physics of the energy transfer processes are often well known. The luminescence characteristics of many other minerals... 

By far the most important activators in mineral luminescence are the iron group ions which exhibit transitions between partly filled d-orbitals. These will dominate the discussion that follows. Luminescence arising from the trivalent rare earth ions occurs in some phosphate minerals but is dealt with elsewhere in this volume (Wright). The filled d-shell ions are activators for cathodoluminescence phosphors such as ZnS, however, most sulfide mineral phases contain too many luminescence poisons for the transitions from these ions to be observed. 

Recently a lot of new information on minerals luminescent under UV lamp excitation appear (MacRae and Wilson 2008) and in several Internet sites (http // www.fluomin.org/uk/contact.php,http //www.csiro.au/luminescence/about.html... 

Theoretical data essential for understanding of luminescence phenomenon may be fotmd in many books, but we believe that for specific field of minerals luminescence the fundamental books of Marfunin (1979a, b) are the best. Below we tried to present very shortly only the mostly essential data especially connected with kinetic considerations, which are the basis of time-resolved technique. 

Our special thanks to Boris Gorobets and Harry Siegel who resently passed away for great contribution in minerals luminescence researh, advice and friendship. 

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