Apatite absorption lines

Such unusual phenomena as reabsorption lines of molecular oxygen and water require a confirmation by an additional independent technique. The best way is to try to detect the corresponding absorption lines by UV-visible spectroscopy. The problem is that sedimentary apatite samples are in the form of non-transparent powder, which is not suitable for optical spectroscopy. The photoacoustic spectroscopy (PAS), which allows measurement of absorption spectra of powdered opaque samples, has been chosen for this purpose (Gaft et al. 1998). PAS works as follows ... 

Absorption lines of molecular oxygen and water in the air (a) and photoacoustic spectra of apatite (b)... 

The estimation of the crystallinity index (Cl) of bone is based on one of the four vibrational modes associated with the apatite phosphate group. In amorphous calcium phosphate, the absorption band at 550-600 cm-1 appears as a single broad peak, whilst in hydroxyapatite it is split into bands of unequal intensity by the apatite crystal field (Sillen and Parkington 1996). Based on the splitting factor introduced by Termine and Posner (1966), Weiner and Bar-Yosef (1990) proposed the use of a crystallinity index to measure the crystallinity of bone mineral. As illustrated in Fig. 4.7, the Cl is estimated by drawing a base line from 750 to 495 cm 1 and measuring the heights of the absorption peaks at 603 cm-1 (measurement a), 565 cm 1 (measurement b) and the distance from the base line to the lowest point between the two peaks (c). Cl is calculated from the formula ... 

It is clearly seen that negative lines are much stronger then the noise. Besides that, the negative lines are always situated at the same places. The invariabihty of the spectral positions provides the evidence that they are not connected with fluctuations of the laser pulses and detection system. Thus it may be concluded that we a deaUng with a reabsorption mechanism. The optical absorption spectra of natural apatites in the range 600-900 nm contain several lines and bands connected with Nd ", Pr ", Mn ", SOj (Gorobets 1975 ... 

Phosphate accessory phases contain a wealth of petrologic and chronological information, but each possesses particular properties that make accurate quantitative microanalysis difficult. This chapter provides an overview of the literature concerned with the main problems of electron microprobe (BMP) phosphate analysis. These include the volatility of fluorine in F-bearing apatite, and the mutual interference of L- and M-line X-rays from the major and trace elements in monazite and xenotime, along with consideration of standards, detection limits, absorption edges, and ZAF corrections in REE phosphates. 

The active participation of Sq level is indirectly accredited by the simultaneous observation of UV and visible emission in cathodoluminescence and synchrotron excited spectra (Fig. 5.8) Excitation into the 4f5d and higher lying bands evidently decays to the Sq level located at 46,300 cm which exhibits luminescence in wide band-gap hosts due to radiative de-excitation to the lower lying levels of Pr. The So- F4 transition at 246 nm is especially strong in oxyapatite. In F-apatite only the line at 269 nm is present. It may be explained by the relatively long-waved absorption edge in fluorapatite, which is at about 300 nm (Morozov et al. 1970). 

Gaft M, Reisfeld R, Panczer G, Champagnon B (1997c) Reabsorption lines of molecular oxygen and water in natural apatite. Opt Mater 8(1-2) 143-149 Gaft M, Trabjerg I, Reisfeld R, Panczer G (1998) Absorption of molecular oxygen and water in apatite by photoacoustic spectroscopy. Spectrochim Acta A 54 1721-1724... 

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