Molecular and atomic emission of fluorine by Laser-Induced Breakdown Spectroscopy using 266, 532 and 1064 nm lasers
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| Year of publication | 2016 |
| Type | Conference abstract |
| MU Faculty or unit | |
| Citation | |
| Description | Several elements as halogens, e.g. fluorine, are difficult to detect by optical emission methods including Laser-Induced Breakdown spectroscopy (LIBS) technique, especially in ambient conditions. Halogens require high excitation energy and the strongest emission lines for halogens are in UV spectral range, where the detection possibility is limited by atmospheric conditions and detection parameters. The emission lines applicable for LIBS analysis are in near IR range (500 nm to 850 nm) with insufficient limits of detection required by many applications1. Molecular LIBS is one of possibilities how to improve the sensitivity for detection of halogens for many years2,3. In this work the CaF molecular bands have been studied in LIBS analysis in respect to the fluorine emission lines in order to achieve higher sensitivity. The effects of different laser wavelengths (266 nm, 532 nm, and 1064 nm) on CaF molecular bands were investigated after the optimization of parameters as energy of the laser pulse, gate delay and gate width value. The experiments were performed in atmospheric ambient conditions on CaF2 crystal samples. These test samples provide high fluorine content thus enabling to perform a comparative study on fluorine atomic and molecular emission. The differences between their intensities may exceed one order of magnitude. The possible application is in detection of presence of fluorine e.g. in rocks, pigments and metallic parts affected by salts. The detection of salts can be distorted by using the partner element in the crystal (e.g. Na, Ca, K) because these elements can also come from other compounds. Molecular spectra can be efficiently measured instead of fluorine emission lines, which are in many cases not detected. The CaF bands were easily observed even in the first microsecond after the laser pulse and they persist several tens of microseconds. In contrast to the excitation energy of halogen atom the dissociation energy of the halogen-based radicals is several units of eV corresponding to the ionization of many alkali and transition metals. The halogen radicals are likely being (re)created and excited permanently throughout the whole existence of the microplasma at least in its peripheral parts. |
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