Element Identification on the Surface of Inorganic Solids by Excimer Laser-Induced Emission Spectroscopy

Abstract

Intense atomic emission lines are observed when the surfaces of minerals, such as pyrite or zinc blende, are excited with UV laser pulses of 8 mJ energy, at a wavelength of 370 nm. The line spectra have been assigned to transitions of the metallic component of the material under investigation, in the neutral charge state of the corresponding atom; a few ionic emissions have also been detected. A nonlinear dependence of the emission intensity on incident laser energy, as well as the observation of transitions at energies higher than the incident photon energy, indicates that multiphoton processes are involved in the ablation and excitation process. The occurrence of the laser-induced emission phenomenon, at the pulse energies used, depends on characteristic properties of the material, such as absorption length, heat capacity, and enthalpy of vaporization. In the experiments, minor components contained in the naturally occurring minerals have been detected with high sensitivity. On the basis of this observation, the potential of the method for trace analysis has been explored. Test solutions containing an ion to be analyzed, such as Pb²⁺, have been applied to the surface of an ablatable copper or sulfur target. From the intensity of the recorded laser-induced Pb emission lines, a detection limit of less than 10 ppm or 35 mg/cm² on the target has been deduced.