This paper shows that the satellite lines that appear in the absorption and fluorescence spectra of neodymium ions in a LaF<sub>3</sub> crystal at concentrations of about 0.5 at.% and the accompanying lines of the isolated ion are caused by pairwise interaction of the Nd<sup>3+</sup> ions. Double optical resonance is used to study the structure of the satellite lines in the neighborhood of the <sup>4</sup>I<sub>9/2</sub>→<sup>4</sup>G<sub>5/2</sub> transition of the isolated ion (wavelength 5777.1 Å), hidden by inhomogeneous broadening. When neodymium ion pairs are excited by resonance laser radiation, the presence of anti-Stokes components is recorded in the fluorescence spectrum (up-conversion). It is shown that the main up-conversion mechanism is cumulative pair excitation. These results are convincing evidence that the suppression of absorption from excited levels can be experimentally observed in condensed media.
© 2011 OSAPDF Article