Trivalent RE ions

Dieke diagram 7 4.1. Calculations of free trivalent RE ions 15... 

Fig. 6. Complete 4f (left) and 4f 15d (right) energy level diagram for all trivalent RE ions.

Calculations of trivalent RE ions in LHF4 4.2.1. Model clusters for trivalent RE ions in LiYF4... 

Fig. 10. Complete 4f and 4f" 5d energy level diagram for all trivalent RE ions in YLF obtained by the first-principles relativistic Cl calculations. For each element, the compositions of the 41" configurations are shown on the left and those of 41 5d configurations are shown on the right, respectively. See text for further explanations.

List of Steven s factors ctj, ftj, yj, for the trivalent RE-ions (from Elliot, 1972) [6]. 

TABLE 8.3 (r1) for the different trivalent RE-ions (from Freeman, 1972) [7], ... 

Figure 17. The variation of the RE-to-phosphate distances is shown as a function of the RE-ion radius for both the monazite- and xenotime-structure orthophosphate compounds. As shown in this figure, the shorter RE-to-phosphorous distances in the monoclinic structure compounds vary linearly with the trivalent RE ion radius with a slope that is close to 1. A similar variation is evident for the RE-P distances in the tetragonal xenotime-structure compounds—a trend that supports the comparison of the [001] polyhedron-P04 tetrahedron chain arrangement in the two structural types (after Ni et al. 1995).

Doping EuSe with additions of LaSe or GdSe produces a shallow donor d level. A transition from the latter to the level of Eu does not occur because this state is located deeper, energy-wise, than Excitation of the electrons into the conduction band therefore takes place at lower temperatures than for SmSe-NdSe alloys. Thus, the electrical conductivity in the case of low concentrations of trivalent RE ions is due to the electrons in the conduction band. At higher concentrations, chains of La or Gd ions form as in the preceding case. 

As noted above, there is a great disparity between the number of RE ions that have been lased and the relatively small number of materials that are actually used in practical applications. Nevertheless, great potential exists forthe future. A summary of all the wavelengths that have been generated by RE ions appears in Fig. 9. (Note that the particular transitions involved have not been indicated on the figure.) The wavelengths span the range from 0.18 /rm to >7 /trm, and both divalent and trivalent RE ions are represented. The efficiencies of many of these systems are extremely low, however, and may never prove to be ttseful in practical circumstances. 

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