a Spectroscopic Study of Energy Transport Between Nickel
Abstract
This thesis contains a spectroscopic study of the dynamics of energy transfer between Ni^ {2+} ions in the two model host systems MgF_{2} and MgO. The static, near infrared properties of Ni^ {2+}, which determine the nature and extent of energy transport in these systems, are also considered. The spectroscopic properties of Ni^ {2+} in the system MgF_2 are considered first. A new luminescent transition is observed from the ^1T_2 to ^3T_1<=vel which allows for the first time, an accurate determination of the ^1T_2 decay at elevated concentrations by a dual channel cross-relaxation process, and from the observed oscillator strengths, the transfer mechanisms are deduced. The temperature dependent non-radiative ^1T_2 decay rate is then measured to predict the properties of a yet unobserved luminescent transition between the ^1T_2 and the ^1 E levels. Fluorescence line narrowing (FLN) is used to accurately measure the ground state splitting in this system and separate the effects of excited state from ground state absorption. Time resolved FLN (TRFLN) is then used to demonstrate the effects of donor-donor energy transfer, in which the migration of energy exhibits an energy dependent transfer rate. This is the first reported demonstration of the use of FLN and TRFLN in the infrared beyond that portion of the spectrum normally accessible by phototubes. The spectroscopic properties of Ni^ {2+} in the system MgO are examined next. Time resolved spectroscopy is used to identify two new luminescence transitions emanating from the ^1T _{rm 2g}<=vel. The increase in the decay rate from the ^1T _{rm 2g}<=vel, at elevated concentrations, is well described by a cross-relaxation process and the multipolar mechanism is determined. Energy transfer to Ni^{2+ }-Ni^{2+} pairs is then considered. It is found that energy transfer from single-ions to pairs dominates the decay characteristics of the first excited state. Ions that contribute to energy transfer may be separated spectroscopically from isolated single-ions and analyzed by a fast diffusion model. Two different types of pair interactions are identified for which the strength of the exchange coupling, the geometry of the superexchange interaction and the magnetic ordering of the pairs are determined. The FLN technique is then used to examine the validity of the fast migration model.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- January 1990
- Bibcode:
- 1990PhDT........90T
- Keywords:
-
- II) IONS IN THE MODEL HOST SYSTEMS MAGNESIUM FLUORIDE AND MAGNESIUM OXIDE (NICKEL(II) IONS;
- MAGNESIUM FLUORIDE;
- MAGNESIUM OXIDE;
- Physics: Condensed Matter; Physics: Optics