Elucidation of the electron transfer mechanism in Eu2+ and Sm3+ codoped

Abstract

Many-electron multiconfigurational ab initio calculations are combined with x-ray spectroscopy to scrutinize a popular model for electron transfer in lanthanide-doped crystals which hypothesizes that the electrons are conveyed by the conduction band of the host. Contrary to this accepted picture, our combined theoreticalexperimental effort shows that the reversible electron phototransfer from Eu 2+ to Sm 3+ in CaF 2 is direct, from metal to metal. It is theoretically predicted and experimentally verified that visible light induces the reverse electron transfer.

A Standalone, Battery‐Free Light Dosimeter for Ultraviolet to Infrared Light

“…It is worth noting that the initial and final states of this charge transfer are well known but that there is still no consensus on how this transfer is accomplished, [47][48][49]51] however it was recently shown that the electron transfer between Eu and Sm in CaF 2 is achieved directly without the involvement of conduction band states. [50,52] To verify the existence of similar valence changes in SrAl 2 O 4 :Eu 2+ ,Sm 3+ , as suggested by Equations ( 1) and ( 2) the phosphor was subjected to a similar X-ray absorption spectroscopy experiment as described in Joos et al [46] . Eu L 3 and Sm L 3 X-ray absorption near edge structure (XANES) measurements performed on SrAl 2 O 4 :Eu 2+ ,Sm 3+ are shown in Figure 3.…”

“…At the DUBBLE beamline the fluorescence emission was detected using a nine-element monolithic Ge detector, while at the SNBL beamline a 13-element Ge detector was used. The fitting procedure for the quantitative analysis of XANES spectra is analogous as the procedure described in Joos et al [46,52] and consisted of a least squares fitting of the difference between the experimental data and the simulated spectra. The spectra were fitted using a Gaussian function to describe the white lines whereas the step-like function, caused by the transition of the 2p 3/2 electron to the continuum or quasi continuum states was described by an arctangent.…”

Making Eu2+- and Sm2+-Doped Borates Fit for Solar Energy Applications

“…All this was done to ensure that the obtained oxidation states are representative of the as-prepared powders. HERFD-XANES spectra at the Eu L 3 and Sm L 3 absorption edges feature a recurrent energy difference of about 7–8 eV between the white lines that correspond to divalent and trivalent ions . This enabled a straightforward assessment of the relative divalent and trivalent ion concentration that scales with the respective intensity ratio.…”

CombinedDFTand wave function theory approach to excited states of lanthanide luminescent materials: A case study ofLaF3:Ce3+

“…Two thus‐obtained CCDs corresponding to different charge states can be further combined to construct charge transfer CCDs [ 31 ] . We note that, this approach is well justified for host materials with high symmetry like fluorite [ 20,21,23,24,26,27,29,30 ] and perovskite [ 22,25,28 ] , for which it is plausible to treat the breathing mode as the dominant vibrational mode relevant in excitation and luminescence processes. Many practical lanthanide luminescent materials have lower symmetry [ 3,4 ] , for which the scan approach is likely to be over‐simplified since different metal–ligand bonds may change differently upon electronic excitation.…”

“…In this framework, a small cluster containing the lanthanide ion and its nearest neighboring ligands is explicitly treated by multi-configurational (MC) wave function theory (WFT) [18] , while the environmental effects of the host compound are represented by the so-called ab initio model potential (AIMP) for short-range interactions [19] and a grid of point charges for long-range electrostatic interactions. Many successful applications have been conducted to excited states of different nature, including 4f nÀ1 5d 1 states [20][21][22][23] , inter-valence charge transfer (IVCT) [24][25][26][27] , metal-to-metal charge transfer (MMCT) [28][29][30] and ligand-to-metal charge transfer (LMCT) [28] . This approach has accessibility to complex manifold of excited states and gives accurate energy levels and transition intensities, for example, resulting in an error around 300 cm À1 for Eu 2+ and Eu 3+ doped alkaline earth metal fluorides and sulfides [23] .…”