Inhomogeneous broadening of Cr3+ luminescence in doped LiTaO3 -: art. no. 214104

A theoretical model of the effect of inhomogeneous broadening on the luminescence lineshape of Cr3+ is developed and applied to the disordered system Cr3+:LiTaO3. At ambient pressure, Cr3+ occupies primarily low-field sites in LiTaO3 and exhibits broad (4)T(2 -->)(4)A(2) emission. The induction of a low-field --> high-field transition with pressure led to the stabilization of narrow, well-resolved E-2 --> (4)A(2) emission and permitted us to determine that Cr3+ occupies two crystallographically distinct low-field sites at ambient pressure. These two sites were incorporated into a comprehensive electronic-structure model for Cr3+ that included the effects of spin-orbit and vibronic coupling to assess the influence of inhomogeneous broadening on the spectral lineshape. The model predicts that each of the two low-field sites is best described in terms of a Gaussian distribution of T-4(2) and E-2 energies. The model further indicates that the T-4(2) and E-2 energies within each Gaussian distribution are inversely correlated. The model successfully describes the emission lineshape, linewidth, and intensity of Cr3+ over a wide range of temperature and pressure, including during the low-field to high-field electronic transformation. A tentative molecular description of the different Cr3+ sites is also presented.