Luminescence properties of Cu2+-doped TMA2MnBr4crystals and a spectroscopic study of the CuBr42-complexes formed

Investigates the influence of Cu 2+ impurities on the luminescence properties of TMA 2 MnBr 4 :Cu 2+ as well as the local structure and orientation of the CuBr 4 2- complexes formed, by means of the excitation and luminescence spectra, lifetime measurements and polarized optical absorption spectroscopy in the 10-300 K temperature range. It is demonstrated that the presence of an intense Br - to Cu 2+ charge transfer (CT) band at 555 nm strongly favours a direct energy transfer from Mn 2+ to the non-luminescent Cu 2+ impurities. The influence of this energy transfer on the Mn 2+ luminescence intensity, lifetime and bandshape is analysed as a function of the Cu 2+ concentration. The results are compared with previous ones obtained in one-dimensional Cu 2+ -doped TMAMnCl 3 and TMAMnBr 3 crystals. Two x, y-polarized bands at 18000 and 28400 cm -1 , and two z-polarized bands at 23800 and 36100 cm -1 are observed in the CT spectra of TMA 2 MnBr 4 :Cu 2+ . Their transition energies as well as their polarization are explained in terms of D 2d symmetry distortions of the CuBr 4 2- tetrahedra. The authors also analyse the triplet structure observed in the first CT band which is associated with the tetrahedral 2 T 1 CT state, which is split by the effect of both the static D 2d distortion and the large spin-orbit coupling of the Br - ligands. The absence of discontinuities in the evolution of the CuBr 4 2- CT bands with temperature supports the finding that no structural phase transition occurs below 270 K in these crystals.