Pressure-induced luminescence from broadband to narrow-line emission in Cr³⁺-doped LiCaAlF₆ at room temperature

Abstract

This work investigates pressure-induced excited-state-crossover phenomena in Cr³⁺-doped LiCaAlF₆ at room temperature. The aim is to find the structural requirements yielding the change in the Cr³⁺ photoluminescence (PL) behaviour from a single broadband emission, which is located at 1.62 eV (765 nm) at ambient conditions, to a ruby-like narrow-line emission at 1.87 eV (662 nm). For this purpose, emission and excitation spectroscopy as well as lifetime measurements as a function of pressure were performed in the 0–35 GPa range. Interestingly, we have been able to transform the broadband Cr³⁺ PL at ambient pressure into a ruby-like emission at 28 GPa. This behaviour, together with the variations of the ²E and ⁴T₂ excited-state energies, and the PL lifetime with pressure, can be explained on the basis of the electron–ion coupling associated with the ⁴T₂ and ²E states.

Keywords:

• Spectroscopy
• High pressure
• Photoluminescence
• Cr³⁺
• Excited-state crossover

Acknowledgements

Financial support from the MEC (Project Ref. MAT2005-00099) is acknowledged. F.R. and I.H. thank the support from the University of Cantabria through the Research Intensification program I3. M.N.S. thanks the MEC for a FPU grant (Ref. AP-2004-5954).