Influence Of Charge Transfer State Research Articles

Influence of charge transfer state on Eu3+ luminescence in LaAlO3, by high pressure spectroscopy

The contribution presents spectroscopic characterization of LaAlO3 doped with 0.5 mol %. Eu3+. We measured steady state luminescence, luminescence excitation spectra, as well as the time resolved spectra and luminescence kinetics. The experiments were performed at high hydrostatic pressure applied in diamond anvil cell (DAC) which was changed from ambient to 250 kbar. We found that for all pressures the emission from the 5D0 and 5D1 excited emitting state of Eu3+ was delayed in time after excitation pulse whilst emission from the 5D2 appear immediately after excitation. At pressure above 12 kbar the strong magnification of the luminescence lines related to the transitions from the 5D3 state which were very weak at ambient condition is observed. The emission decay of the 5D3 luminescence become slower when pressure is increased. All these effects are attributed to pressure-induced increase of the energy of the ground electronic configuration 4f6 of the Eu2+ with respect to the valence band edge which results in the charge transfer state, and 5D3 level crossing.

Broadband down-conversion based near infrared quantum cutting in Eu2+–Yb3+ co-doped SrAl2O4 for crystalline silicon solar cells

Near infrared (NIR) quantum cutting involving the down conversion of an absorbed visible photon to emission of two NIR photons was achieved in SrAl2O4:0.01Eu2+, xYb3+ (x=0, 1, 2, 5, 10, 20, 30mol%) samples. The photoluminescence properties of samples in visible and NIR regions were measured to verify the energy transfer (ET) from Eu2+ to Yb3+. The results demonstrated that Eu2+ was an efficient sensitizer for Yb3+ in the SrAl2O4 host lattice. According to Gaussian fitting analysis and temperature-dependent luminescence experiments, the conclusion was drawn that the cooperative energy transfer (CET) process dominated the ET process and the influence of charge transfer state (CTS) of Yb3+ could be negligible. As a result, the high energy transfer efficiency (ETE) and quantum yield (QY) have been acquired, the maximum value approached 73.68% and 147.36%, respectively. Therefore, this down-conversion material has potential application in crystalline silicon solar cells to improve conversion efficiency.

Influence of charge-transfer state on luminescence properties of Eu(III) complex with o-phenylenedioxydicarboxylic acid

The Na[Eu(C 10H 8O 6) 2(H 2O) 2].4H 2O ( 1) crystals has been synthesized. Absorption, emission, and excitation spectra at 293, 77 and 4 K as well as the luminescence decay time measurements were applied to characterize the photophysical properties of the crystals. Strong temperature dependence of the luminescence decay time suggests that the ligand-to-metal charge-transfer state of Eu(III) deactivates the ligand excited state so that the energy transfer from ligand triplet state to metal ion levels does not occur. A correlation between spectroscopic properties of the complex in solid state and in solutions was made. The study for different pH values and various metal:ligand molar ratios showed the existence of more than one form of the complex where ML and ML 2 forms dominated.

Theory of Optical Spectra Involving Charge Transfer States: Dynamic Localization Predicts a Temperature Dependent Optical Band Shift

The influence of charge transfer states on the optical line shape of chromophore complexes is investigated in a minimal model that includes a coupling between an excited state and an optically dark charge transfer state. In the calculations of the absorption spectrum, an intensity borrowing by the charge transfer state, strong vibrational sidebands, and a temperature dependent shift of optical transitions are obtained. The theory is applied to the bacterial photosynthetic reaction center to explain a 30 nm blueshift of the low-energy absorption band with increasing temperature.

Influence of charge-transfer states on the Eu(III) luminescence in mononuclear triple helical complexes with tridentate aromatic ligands

The photophysical properties of a series of mononuclear Eu-containing 1 : 1 nitrato complexes and 1 : 3 triple-helical complexes with terpyridine, [Eu(tpy) 3] 3+, and 2,6-bis(1'-methylbenzimidazol-2'-yl)pyridine, [Eu(L 1) 3] 3+, are investigated with the aim of unravelling the respective influence of the ligand-to-metal charge-transfer state (LMCT) and of π–π interactions between the ligand strands in the large quenching of the metal-centred luminescence sustained by the [Eu(L i) 3] 3+ complexes, as compared to the nitrato complexes with the same ligand. Both metal-centred and ligand-centred luminescence quantum yield and lifetimes are investigated. The energy of the LMCT state is estimated from the difference measured by cyclic voltammetry between the half-peak potentials of the oxidation of the ligand and of the reduction of Eu III. It is found that the energy of the LMCT state drops considerably in the 1 : 3 complexes with respect to the 1 : 1 compounds, as a result of the cage-like arrangement of the three ligand strands, and that it is the main factor responsible for the luminescence quenching in [Eu(L 1) 3] 3+. Other factors, such as π–π interactions play a minor role only.