Apatite - Photoacoustic Spectrophotometry

It was found that the absorption spectrum of the apatite is characterized by the bands at 775 and 850 nm, which are close to reabsorption bands in the same sample and according to absorption in atmosphere may be connected with molecular oxygen and water, correspondingly (Eig. 5.68). 

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) 

Reabsorption lines of molecular oxygen and water have been detected in time resolved luminescence spectra of certain diamonds. 

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