Date of Award
Pure sciences, Calcium fluoride, Crystals, Holmium, Samarium
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By employing luminescence excitation technique, the crystal field split excited states of the trivalent Holmium and Samarium in CaF2 crystal were investigated. The photon energy range of 18000 to 40000 cm-1 was studied. A great number of sharp spectral lines arising from the trivalent ions were observed. Based on a comparison with calculated free ion energy levels, tentative identifications of the observed levels were made. It was found that the selection rule ΔJ≤6 holds in these systems, and the observed transitions are predominately of electrical dipole character. Approximate energy level schemes of the crystal field split excited states of Ho 3+ in cubic sites were constructed. Similar energy level schemes of the three lowest multiplets of the sextet H state of Sm3+ in cubic sites was also constructed.
In order to study the effect of different symmetries surrounding the trivalent rare earth ions, O2- was introduced into the host crystal by means of heat treatment. It was found that heat treatment in open air changes the point symmetry around the rare-earth ion. By means of the same green luminescence excitation technique it was possible to observe these changes taking place. Based on evidence obtained from excitation, emission and thermoluminescence spectra it is concluded that the symmetry of the crystal field surrounding the rare-earth ions in the as received crystal was predominately cubic in our case.
Comparisons between excitation spectra, absorption spectra, emission spectra and thermoluminescence spectra showed them to be in consistence with each other and with previously obtained results in this laboratory.
By employing low-temperature technique, the two lowest Stark components of the crystal field split ground state (6H5/2) of Sm3+ in a C3v field were estimated. A reasonable agreement between the calculated energy levels and the estimated ones was found.
Attempts were made to study the Zeeman effect and lifetimes in the CaF 2:HO3+ system. The results, however, so far are not conclusive and further work is needed in this direction.
Pai, Siu Ting, "Electronic spectra of holmium(3+) and samarium(3+) ions in calcium fluoride crystals" (1970). Electronic Theses and Dissertations. 8094.