Optical absorption spectra of the tripositive thulium ion in certain nitrate complexes

The optical spectra of triply ionised thulium in thulium, ammonium, magnesium, potassium and sodium nitrate solutions has been recorded for the first time. The second-derivative spectrum reveals interesting results. It is very interesting to note that the broad band of the normal spectrum of thulium nitrate, consisting of closely lying electronic levels above 30000 cm-1, could be well resolved in the second-derivative spectrum. The splittings observed for certain levels in all the complexes in the second-derivative spectra have been successfully explained as arising from the superposition of vibronic transitions on electronic spectra. Radiative lifetimes have been calculated theoretically for the fluorescent levels of the ion in all five complexes.