Optical spectroscopy of the geometrically frustrated pyrochlore Ho2Ti2O7

Optical absorption and fluorescence spectra of Ho3+ in the geometrically frustrated pyrochlore Ho2Ti2O7 have been measured in the 27,000-4000 cm−1 spectral and 295-8 K temperature range. The energy positions of the Stark levels have been deduced. The Judd-Ofelt analysis has been performed by fitting the room temperature absorption spectra, and the calculated Judd-Ofelt parameters have been used to evaluate the Ho3+ radiative transition probabilities and the branching ratio. The obtained results show that although the lowest crystal field levels of Ho3+ in Ho2Ti2O7 are well separated, this separation (104 cm−1) is smaller than that previously suggested on the basis of neutron and magnetic studies (150-166 cm−1).