Vacuum ultraviolet excitation spectra of lanthanide-doped hexafluoroelpasolites

Abstract

Vacuum ultraviolet excitation spectra at ∼10 K have been recorded for 4f N → 4f N −1 5d transitions of Cs 2 NaYF 6 :Ln 3+ (Ln = Nd, Sm, Eu, Tb, Ho, Er, Tm). In these high bandgap hosts the lanthanide ions occupy octahedral symmetry sites. The spectra comprise broad, structured bands and in most cases the individual vibronic structure is not resolved. Simulations of the relative intensities and band positions in the spectra have been made by using parameter values from previous studies and/or by employing values from similar systems or estimating trends across the lanthanide series, without data fitting or parameter adjustments. The agreement with experimental results is reasonable except where the luminescent state being monitored is not efficiently populated nonradiatively from the 4f N −1 5d state, or where additional bands are present. The latter are readily assigned to charge transfer transitions or the near-excitonic band. Comparison of the spectra has been made with those of other high symmetry lanthanide ion systems.

4f–5d Transitions of Tb3+ in Cs2NaYF6: The Effect of Distortion of the Excited-State Configuration

“…The pure electronic transitions to T 1g states from the 7 F 6 electronic ground state are expected to manifest sharp features because they are potentially magnetic dipole allowed. However, since the terminal multiplets in this spectral region correspond to 5 I J (J = 4, 5, 6) and 5 K 9 , the transitions are calculated to be very weak in intensity. This is supported by the fact that no weak, sharp bands are apparent in this region.…”

“…The synthesis of materials and the experimental details have been summarized elsewhere. 5,9,10 Low-temperature excitation spectra were recorded for different crystals of Cs 2 NaY 0.99 Tb 0.01 F 6 by two different research groups at the HIGITI station of the DESY synchrotron. The absorption spectrum was recorded for a crystal of Cs 2 NaY 0.9 Tb 0.1 F 6 at higher resolution at CityU using a xenon lamp, an Acton 0.5 m monochromator, and a backilluminated SpectruMM CCD detector.…”

VUV spectroscopy of lanthanide doped fluoride crystals K2YF5

“…The specific shape of the measured CT band with some dip at ~7.45 eV can be related to the presence of some uncontrolled impurities which absorption competes with that of Eu 3+ ions. It should be mentioned that the CT energy in fluoride crystals is typically shifted by ~ 0.23 eV toward lower energy when the temperature increases from 8 K to 300 K [26]. Thus, the CT energy in K2YF5:Eu 3+ crystal gets the value of 7.48 eV at 300 K. On the other hand, the energies of 4f-5d transitions are weakly dependent on temperature and so the temperature of measurements of 4f-5d excitation spectra will be ignored in the forthcoming calculations.…”

“…The spectrum shows several relatively narrow bands, most of which can be ascribed to transitions from the ground 4f 5 ( 6 H5/2) state to different crystal-field states of excited 4f 4 5d 1 configuration of Sm 3+ ion (they are numbered in Fig. 4 in a rather arbitrary way) by taking into account that excitation spectrum as well as each excitation band can show additional features due to electronelectron and spin-orbit interactions [26]. However, as in the case of Eu 3+ ion, the detailed energy level structure of the excited 4f 4 5d 1 electron configuration of Sm 3+ is not considered within the present manuscript.…”

Effects of chemical composition on the structural stability, elastic, vibrational, and electronic properties of Cs2NaLnX6 (Ln = La…Lu, X = F, Cl, Br, I) elpasolites

“…Since there is very few experimental data about the band gaps of Cs 2 NaLnX 6 elpasolites, the isostructural compounds Cs 2 NaYX 6 (X = F, Cl, Br) were chosen as the benchmarks for such an evaluation, as their band gaps can be easily estimated from the observed exciton creation energies given by Ref. 46,47. The calculated band gaps of Cs 2 NaYX 6 (X = F, Cl, Br) using the WC1PBE and PBE0 are collected together with their experimental values in Table S19 of Supplementary Information file.…”