Photoluminescence properties of V-doped La0.67Ca0.33Mn1−xVxO3

The optical spectra have been investigated for a prototypical double exchange ferromagnetic La_0.67Ca_0.33MnO₃ with Mn substituted by V above the paramagnetic-magnetic transition temperature T_C. The excitation spectra under the probe wavelength of λ_em = 473 nm for all samples exhibit two activation bands around 360 and 294 nm, involving an electron transfer from oxygen 2p states to the Mn d states in MnO₆ octahedra. The photoluminescence spectra at λ_ex = 290 nm have the similar spectral features for all samples. The photoluminescence spectral peaks located at 400, 473, 534, 670, 738 and 770 nm, and the corresponding photon energy is in a broad range of 3.1-1.6 eV, indicating that the PL bands could have the different origin: the self-trapped excitons localized on MnO₆ octahedra; the interband transition between the O 2p and Mn 3d bands; the transition between the 3d electron states of Mn ions. So, it can be clearly seen that the electronic behavior above T_C is very complicated. Our results suggest that the charge transfer from O 2p to Mn 3d has the important effects on the electronic structure, and it not only contributes to the optical transition but is helpful and even important to understand the electric, magnetic and thermal properties etc. due to the strong correlation among charge, spin and lattice in perovskite manganites.