f-f transitions of Nd+ in the crystal field

Nd+ ist ein wichtiges Seltenerdion in molekularen Komplexen und Kristallen mit Anwendungen als Magnet, Nd-YAG laser und Absorptionsglas. Es hat Absorptionsbanden im sichtbaren Bereich des Spektrums. Einige dieser Absorptionsübergänge sind "hypersenitiv", d.h. die Intensität solcher Übergänge werden stark von der Umgebung des Ions beeinflußt. Deshalb ist das Wissen über den Anregungsprozess in speziellen Symmetrien so wichtig um Eigenschaften von Neodymiumkomplexen zu verbessern. In dieser Arbeit werden die Energieniveaus des freien Nd+ Ions und Kristallfeld von 6 Wassermolekülen untersucht.Zuerst werden die gruppentheoretischen Grundlagen für Übergänge in der T'_h Doppelgruppe für den Grundzustand 4I und die ersten Anregungszustände behandelt. Dies geschieht unter Berücksichtigung von Spin-Bahn Kopplung in den Russell-Saunders Multipletts und von Kristallfeldeffekten. Vor allem das hypersensitive Niveau 4G_Nd+ is an important rare earth ion in molecular complexes and crystals with applications as magnets, the Nd-YAG laser and absorbing glasses. It has absorptions in the visible range. Some of these are hypersensitive, i.e., their intensity is sensitive to the surrounding of the ion. Therefore the knowledge of the excitation process in a special symmetry is important to improve the properties of Neodymium complexes.In this work the energy levels of the free Nd+ ion and in the crystal field of six water molecules having T_h symmetry was investigated.First, the group theoretical basis for the transitions has been derived based on the double group T_h including the ground state 4I and the first few excited states. The effect of spin-orbit coupling in the Russell-Saunders multiplets as well as the effect of crystal field is accounted for. From the higher states, the hypersensitive level 4G_ The energy levels belonging to the same Russell-Saunders multiplet can penetrate each other after splitting in the crystal field.Second, relativistic calculations were performed with the COSCI method using the X2C Hamiltonian without and with inclusion of the spin-other-orbit coupling. The first 120 energy levels were computed resulting in a complicated picture of distinct energies. The proper assignment could not be solved without further work.The third task in this work was the computation of the different energy levels with increasing speed of light simulating the decrease of spin-orbit coupling in the T_h crystal up to the non-relativistic limit. With the help of these results, the assignment of all 17 energy levels to the correct multiplets could be performed for the ground state, as well as the large number of states for the excited multiplets.The assigned energy levels in the relativistic calculation are in good agreement with experimentally found assignments in an elpasolite crystal in O_h symmetry.Jan Michael SenekowitschZsfassungen in dt. und engl. SpracheGraz, Univ., Dipl.-Arb., 2014(VLID)33702