For calculating oscillator strength of the overlapped
peaks, the area of the peaks was estimated by extrapolating up to
the base line. In order to estimate the intensities for the transitions
3H4→3P2,1,0, it is first noted that the base line for the absorption is
rising towards the higher frequency side. Since the peaks are distinct
we extended the two sides of individual lines linearly to this
base line and measured each such triangular area. In the region of
overlap, the proportion of intensity contributed by different transitions
is so adjusted that the relative intensities as estimated by
the peak height are not unduly modified. The experimental oscillator
strengths, which measure the intensity of absorption transitions
from the ground 3H4 level to various excited levels, have been measured
by Eq. (1) and the values are given in Table 2. The transitions
3H4→3P2 and 3H4→3F2 of Pr3+ ions have been labeled as hypersensitive
transitions as these transitions are strongly dependent on
the neighbouring ligands [24] and these obey the selection rules:
S=0, L≤2 and J≤2 [25].