Pseudoquadrupolar hypersensitive transitions

Fig. 3. Energy levels of eleven trivalent lanthanides below 43000 era-. The quantum number J is given to the right of each level, whereas the multiplicity (2S + 1) and L-value are only given to the left for such levels, where Russell-Saunders coupling is a good approximation. The black triangles give the levels most frequently found to fluoresce. The squares indicate levels to which transitions from the groundstate have pronounced pseudoquadrupolar hypersensitive character, and hence intensity in certain materials. The stippled lines indicate calculated positions of J-levels not yet identified. The diagram is taken from Ref.231...

For our purpose of discussing thermoluminescence, the main problem is whether the observation that the strong, narrow bands in an overwhelming majority of cases are due to pseudoquadrupolar transitions can be explained by their molar extinction coefficient s being particularly high in the mixed oxides, or whether additional effects operate in favour of hypersensitive luminescence. If we neglect reflection of fight from the sample. 

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