Luminescence radiation-induced centers

Fig. 4.14. a-f Laser-induced time-resolved luminescence spectra of calcite demonstrating Mn ", Pb " and radiation-induced centers... 

Luminescence of Pr + in zircon is very difficult to detect under UV excitation even by time-resolved spectroscopy. The reason is that it has a relatively short decay time similar to those of radiation-induced centers. Visible excitation, which is not effective for broadband luminescence, allows the revealing of Pr + luminescence lines, using high-resolution steady-state spectroscopy. Under such experimental conditions each element has individual lines, enabling confident identification of the spectrum to be possible (Gaft et al. 2000a). Only if radiation-induced luminescence in zircon is relatively weak, the lines of Pr may be detected by UV excitation (Fig. 4.38c). 

The violet emission of the radiation-induced center (COs) " is well known in steady-state luminescence spectra of calcite (Tarashchan 1978 Kasyanenko, Matveeva 1987). The problem is that Ce also has emission in the UV part of the spectrum. In time-resolved luminescence spectroscopy it is possible to differentiate between these two centers because of the longer decay time of the radiation-induced center. Its luminescence peaking at 405 nm becomes dominant after a delay time of 100-200 ns while emission of Ce is already quenched (Fig. 4.14f). 

Fig, 5.66. Laser-induced time-resolved luminescence spectrum (a) and excitation spectrum (b) of radiation induced center in calcite... 

Certain similarity may be seen between this luminescence and short-Hved orange emission in calcite, which has been ascribed to radiation-induced center (Fig. 5.67). It is possible that natural irradiation may be a reason of orange luminescence in apatite also. 

X-ray Fluorescence Spectrometry and Inductively Coupled Plasma analysis reveal the presence in the zircons of all existing REE. The steady-state luminescence in natural zircons is dominated by broad emission arising from radiation-induced centers and narrow emission lines of Dy " (Trofimov 1962 Tarashchan 1978). These emissions obscure the spectra of other REE. The thermal treatment enables to solve this problem in certain cases using the fact that the intensity of broad band luminescence quickly decreases after heating at 700 °C-800 °C, while the intensities of the REE lines remain nearly constant (Shinno 1986, 1987). Even after heating the samples not all the REE can be identified by steady-state spectroscopy since the weaker luminescence lines of certain REE are obscured by stronger luminescence of others. For example, luminescence of Pr " is difficult to... 

Fig. 5.108 (a-d) Luminescence (a), decays (b, d) and excitation spectra (c) of blue radiation-induced centers in calcite... 

Nevertheless, such interpretation cmitradicts the fact, that after heating at 800 °C the short-lived yeUow band disappeared and a usual long-lived Mn luminescence becomes visible (Fig. 5.111c, d). Time-resolved excitation spectrum of short lived yellow band consists of one main broad band with extremely low Stocks shift and is absolutely different from those for Mn + (Fig. 5.11 le-f). Certain similarity may be seen between this luminescence and short-lived orange emission in calcite, which has been ascribed to radiation-induced center. It is possible that natural irradiation may be a reason of orange luminescence in apatite also. 

Figure 6.13 presents PIE spectra of other luminescence centers different from trivalent RRE which present in well known luminescent minerals green luminescence centers of uranyl adsorbed by quartz (Fig. 6.13a), Mn in willemite (Fig. 6.13b) and calcite (Fig. 6.13c) with green and orange luminescence, correspondingly, blue emission of radiation-induced center in calcite (Fig. 6.13d) and red...

Fig. 6.26 (a-d) Short-lived orange luminescence spectrum (X x = 532 nm) of radiation-induced center in calcite and its decay as a function of delay time (a). Gated Raman spectra with excitation at 532 nm and gate widths of 10 ns (b) and 0.5 ns (d). CW Raman spectrum with excitation at 785 nm (c)... 

Ionic radii of zirconium are of 0.73 A in 4-coordinated form and 0.86 A in 6-coordinated form. The possible substituting luminescence centers are Ti with an ionic radius of 0.75 A in 6-coordinated form, TR +, Cr +, Cr +, Mn ", and Fe. Impurities ofU and Th are also possible, which may radiatively decay with formation of radiation induced luminescence centers. 

Fig. 4.39. a-d Laser-induced time-resolved luminescence spectra of zircon demonstrating intrinsic radiation induced, luanyl and Fe center... 

Fig. 5.65. Comparison of radiation-induced luminescence and EPR of different centers as a fimction of the heating temperature. Left integrated yellow liuninescence (upper) and EPR of TF, Yh, Nh and SiO (lower). Right yellow luminescence bands of different origin with different thermal stability (Gaft et al. 1986)...

In nature, RE and Mn " can substitute for Ca, becoming luminescence centers in the crystallographic environment. Most calcite luminescence is attributed to Mn ", while Mn " hides rare earth emission, and so far their luminescence in calcite is rather poorly characterized (Blasse and Aguilar 1984 Pedone et al. 1990). The lines of Sm " and Dy " have been confidently established using a hot cathode cathodolu-minescence method (Haberman et al. 1996). Besides that, luminescence of Pb " (Tarashchan 1978) and radiation-induced are known (Kasyanenko and... 

The natural aragonite in our study consisted of 12 samples from a variety of geologic environments. By using laser-induced time-resolved spectroscopy we were able to detect evidently Mn, Ce ", Eu " and broad luminescence band peaking at 580 nm with very short decay time of approximately 20 ns, which by analogy with Terlingua-type calcite may be preliminary ascribed to radiation-induced luminescence center (Fig. 4.22). 

Radiation induced luminescence centers and radiation influence on the luminescence properties of the other emission centers become more and more important both theoretically and for different applications (Nasdala et al. 2013). 

Figure 6.14 presents PIL of several centers which are characterized by short and very short intrinsic decay times, such as 1300 ns for Eu in fluorite Cap2 (Fig. 6.14a), 20-30 ns for orange luminescence in calcite (Fig. 6.14b) and 25-30 ps for radiation induced yellow luminescence of zircon ZrSi04 (Fig. 6.14c). Such luminescence detection after delay time of 125-150 ps, where it has to be totally quenched, implies that the life time of luminescence is actually much longer than decay time determined by intrinsic transition probabilities. Actually, it is three orders of magnitude longer.

Resonant interactions are ordinarily much stronger than non-resonant ones. Each characteristic frequency is actually a band of frequencies of width Av more or less symmetrically distributed around the same center vq. The resonant transfer of energy from a radiation field to matter is called absorption. The absorption process ereates also an induced dipole moment, but a larger one than in the case of polarization. The transfer of energy from matter to the radiation field is termed emission (or luminescence). We... 

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