Thermally modulated ultraviolet absorption spectra of CaF:Ce 3+ crystals

The thermally modulated absorption spectra (TMA) of Ce 3+ in CaF 2 , crystals at 90 K show the zero‐phonon and vibronics of the 4f → 5d ∣ε〉 transitions. They are more distinctive than that in the conventional absorption spectra. In TMA, the absence of the overlapping background in the composite band between ≈32000 and ≈34000 cm −l enables one to compare the band widths of various orders of vibronics readily and hence to reveal the possible presence of the weak and/or broad 4f → 5d ∣θ〉 absorption at ≈33100 cm −l .