EUV spectra of Gd and Tb ions excited in laser-produced and vacuum spark plasmas

Extreme UV spectra of the gadolinium and terbium ions excited in the laser-produced plasma and vacuum spark sources were recorded in the 40-120 angstrom region and investigated on the basis of the Hartree-Fock calculations using Cowan code. The intense peaks in the 65-75 angstrom region of the vacuum spark spectra were interpreted as a manifold of the 4d(10)4f(m)-4d(9)4f(m+1) transitions in the ions with a partially filled 4f shell. The drastic narrowing of these peaks was observed in the spectra of the laser-produced plasma. It was explained by a change of the 4d(10)4f(m)-4d(9)4f(m+1) (m > 2) transition arrays mostly contributing to the intensity of the peaks in the vacuum spark spectra for the 4-4 transitions in the simplest spectra of the 4p(6)4d(k) (k = 8-10) and 4d(10)4f(m) (m = 1-2) ground configuration ions predominantly excited in hotter laser-produced plasma. The most intense lines of the 4d(10)4f(2)-4d(10)4f5d transitions in the Gd XVII and Tb XVIII spectra were classified for the first time.