RESUMEN
The ultraviolet photoelectron spectrum of the [EMIM][B(CN)4] ionic liquid was recorded and analyzed. Together with different ab initio calculation methods, detailed insight into the electronic structure of this simple room temperature ionic liquid is possible. The ion-pair approximation to the liquid electronic structure was not sufficient. Therefore bulk ab initio calculations were performed on a proposed crystal structure. The modelling of bulk electronic spectra is able to explain the experimental electronic structure of the ionic liquid. Most notably, the dispersion corrected PBE calculation (PBE-D3BJ) showed good agreement with the experimental UPS spectrum. The spectra simulated by the B97-D and the BLYP-D3(BJ) functionals were also in agreement with the experimental data. The LDA approximation only provided qualitative agreement while the optB88-vdW and CX-vdW functionals were not good. However, it will be shown that many requirements have to be met in order to accurately describe the electronic structure of this ionic liquid.
RESUMEN
The ultraviolet photoelectron spectrum (UPS) of the [EMIM][BF4] ionic liquid was recorded and analyzed. Together with the gas-phase UPS spectrum of the [EMIM][BF4] vapor and ab initio calculation methods, detailed insight into the electronic structure of this simple ionic liquid is possible. The low binding energy tail in the UPS spectrum is about 7.4 eV, in agreement with previous estimations of the HOMO-LUMO gap of the [EMIM][BF4] ion-pair. The bulk ab initio calculations are able to explain most of the features in the spectrum. However, DFT consistently lacks accuracy in the description of the top of the valence band. The dispersion corrected PBE calculation (PBE-D3) did offer very good agreement with the experimental structure, but the recently-developed vdW-DF functionals C09, optPBE, optB88 and CX were found to offer the best agreement in terms of the electronic structure.
RESUMEN
We carried out a combined study of UV-VUV luminescence and resonant x-ray emission from BeO single crystals with incident photon energies in the vicinity of the Be 1s absorption edge. The x-ray emission spectra show that at the Be 1s photoabsorption edge the lattice relaxation processes in the excitation site take place already on the timescale of the radiative decay of the core excitation. Comparison of the x-ray emission and the luminescence spectra indicates that the maximum energy loss of the process of lattice relaxation during the decay of inner-shell holes is similar to the loss that occurs in the self-trapping process of valence excitons. The possible decay channels of core excitations have been discussed and the mechanism for the creation of 5.2 eV luminescence at the photoabsorption resonances has been suggested.
