Emission characteristics of nickel ionic lines excited by reduced-pressure laser-induced plasmas using argon, krypton, nitrogen, and air as the plasma gas
Spectrochimica Acta Part B 62 (2007) 1303–1310
Abstract
The emission characteristics of nickel ionic lines in low-pressure laser-induced plasmas are investigated when argon, krypton, nitrogen, or air
gas was employed as the plasma gas. The spectrum patterns and the relative intensities of the ionic lines are measured with and without a blind
cylinder surrounding the sample surface to separate the detected emission area into two portions roughly: an initial breakdown zone and an
expansion zone of the plasma. Their emission intensities are strongly dependent on both the kind and the pressure of the plasma gas. Different
major ionic lines are observed in the argon and the krypton plasmas: for example, the Ni II 230.010-nm line (8.25 eV) for argon and the Ni II
231.604-nm line (6.39 eV) for krypton. The excitation mechanism of these ionic lines is considered to be a resonance charge-transfer collision
with argon or krypton ion due to good energy matching to the corresponding energy levels of nickel ion. These ionic lines measured with the blind
cylinder at reduced pressures of around 1300 Pa give the largest signal-to-background ratios; therefore, the analytical application under such
optimum plasma conditions is recommended.