Laser-induced breakdown spectroscopy of environmental and synthetic samples using non-intensified CCD: optimization of the excitation wavelength

Laser-induced breakdown spectroscopy (LIBS) is a technique increasingly used to perform fast semi-quantitative multi-elemental analyses of various materials without any complex sample preparation, being also suitable for in situ analyses. Few studies have been performed to understand the influence of laser wavelength on LIBS analytical performance on environmental samples. The main goal of this study was to perform a comparative elemental analysis of a number of soils, citrus leaves, and synthetic solid matrices using two different wavelengths, i.e., 532 and 1064 nm of Nd:YAG lasers, and a spectrometer coupled to a non-intensified charge-coupled device camera as the detection system. The emission lines with higher upper energy level, i.e., C I--193.03 (7.685 eV) and Si I--212.41 nm (6.616 eV), were more intense when using the 532 nm than the 1064 nm laser light, whereas the opposite occurred for elements with lower upper energy level, i.e., Ti I--336.12 nm (3.716 eV) and Fe I--368.75 nm (4.220 eV). The observed increase in LIBS signal between the two wavelengths is about 30-50%. The relationship between the line emission intensities and the used excitation wavelengths were associated to the upper level energy of the element.