Efficient non-photochemical spectral hole burning in single-crystal SrO: Co²⁺

Efficient non-photochemical spectral hole burning is observed in the zero phonon line at 740 nm of Co²⁺ doped in single-crystal SrO. The Co²⁺ ions substitute for Sr²⁺ ions and occupy 〈1 1 1〉 off-centre positions in SrO. Due to strain and a distribution of internal electric fields in the host crystal the eight equivalent sites can have different energies and different transition frequencies. The hole burning is attributed to light-induced rearrangements between these eight sites. Such a process can be described in terms of the two-level systems model normally used for photophysical hole burning of glasses. The efficiency of the hole burning process is determined to be ≈ 0.07. Also, the luminescence spectrum of the lowest excited state at 1300 nm is reported.