Document Type

Dissertation - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Chemistry and Biochemistry

First Advisor

Stanley May


These projects were focused on the laser spectroscopy of trivalent lanthanide ions doped or co-doped in the CsCdBr3 crystal lattice in which Ln3 +-Ln3+ pairs are formed due to the unique structure and charge compensation requirements. Following are the outlines of the three research projects.

The time-dependence of thermalization between the 3P0 and 3P1 electronic states of Pr3+ in CsCdBr3 was investigated. The energy gap between the 3P0 and 3 P1 states of Pr3+ doped in CsCdBr3 is about 570 cm-1, which can be bridged by three or four phonons of the host matrix. In order to investigate the multi phonon absorption and emission involving these two levels, Pr3+ ions were co-doped with Gd3+ ions in CsCdBr3 with a high molar ratio of Gd to Pr (0.025%Pr, 1.5%Gd), so that the majority of Pr ions are in Pr-Gd pairs.

In Pr-Gd pairs, there are no cross-relaxation processes involving the 3P1 and 3p0 states of Pr3+ ions. When Pr3+ is excited to the 3P1, or 3P0 state, relaxation is determined by luminescence from 3P1, and 3P0, by 3P1à 3P0 multiphonon emission, and by 3P0à 3P1 multiphonon absorption. Four coupled differential equations describing the relaxations of 3P0 and 3P1 following different excitations were obtained. These equations were used to IV fit the time-dependence of the luminescence from 3P1 and 3P0, and thereby to obtain the rate constants for the 3P1 à 3P0 multiphonon emission, and by 3P0à 3P1 multi-phonon absorption transitions. These rate constants were obtained in the temperature range 8-340 K.

Investigation of the mechanisms and temperature-dependence of the cross[1]relaxation processes in Pr-Pr pairs in CsCdBr3 following excitation into the 3P1 state of Pr3+. CsCdBr3 crystals doped with 0.12% Pr was made to study cross-relaxation between Pr ions in Pr-Pr pairs. The excited 3P1 state of Pr3+ was quenched extremely rapidly through a cross-relaxation process involving the neighboring Pr3+ in the 3H4 state. This cross-relaxation process was too fast to measure on the time-scale of our experiments (~20 ns). Reverse energy transfer from the 1D2 state of the acceptor ion back to the 3P1 state of the initial donor ion was also found. The equilibrium between the 3P1 state of the donor and the 1D2 state of the acceptor was proved by the emission spectra and kinetic data of these two excited states.

The initial cross-relaxation from 3P1 leads to two intermediate excited states, 3H6 and 1D2 in the Pr-Pr pairs. A second step of cross-relaxation between these intermediate states produced one P3+ ion in the 3P0 excited state and one Pr3+ ion in 3H4 ground state. The rate of the second cross-relaxation is moderately fast and increases with temperature. This rate constant was measured from 8 to 170 K.

Energy transfer from Tb3 + 5 D3 to Pr3+ in Pr-Tb pairs in CsCdBr3 and its temperature dependence was studied. CsCdBr3 crystals co-doped with Pr3+ and Tb3+ were made for the investigation of cross-relaxation between Pr3+ and Tb3+. The cross- relaxation of the 5D3 state of Tb3+ by Pr3+ was evidenced by a strong emission from the 3P1 state of Pr3+ following the selective excitation of the 5D3 state of Tb3+. The rate constants of the cross-relaxation were obtained from the time-dependence of the luminescence from both the 5D3 state of Tb3+ and the 3P1state of Pr3+.

Two pathways of energy transfer are possible. One is the energy transfer from the 5D3 of Tb3+ ions to excite the Pr3+ ions to the 3P1 state; the other is to excite the Pr3+ to 3 P2. It is not possible to observe the emission from the 3 P2 due to its fast multiphonon relaxation to the 3P1. However, the temperature dependence of the cross-relaxation rate constants follow the same trend as that of the total overlap of the emission spectrum of the 5D3 with the excitation spectra of the 3P1and 3P2. This indirectly indicates that both the 3P1 and the 3P2 states of Pr3+ ions are involved in the cross-relaxation of the 5D3 state of Tb3+ ions.

Library of Congress Subject Headings

Rare earth metals -- Spectra.
Laser spectroscopy.
Relaxation phenomena.
Energy transfer.


South Dakota State University



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