The terbium chloride–aluminum chloride vapor system. I. Absorption and excitation spectra

The absorption spectrum of the vapor complex formed at elevated temperatures between TbCl3 and AlCl3 has been measured in the region 20 000–50 000 cm−1. Oscillator strengths of f–f absorption bands below 37 000 cm−1 were determined. Strong absorption due to opposite parity 4f75d states was observed in the 37 000 to 50 000 cm−1 region with a peak molar absorptivity of approximately 500 ℓ/mol cm. Significant additional absorption attributed to a molecular complex was also observed in this region. By measuring the excitation spectrum it was found that the molecular absorption does not appear to lead to fluorescence of the 5D4 state. In contrast, absorption by the 4f75d states does result in strong 5D4 fluorescence.