Configuration-selective spectroscopic studies of Er[sup 3+] centers in ErSc[sub 2]N@C[sub 80] and Er[sub 2]ScN@C[sub 80] fullerenes (original) (raw)
Related papers
Physical Review Letters, 2008
Systems exhibiting both spin and orbital degrees of freedom, of which Er 3+ is one, can offer mechanisms for manipulating and measuring spin states via optical excitations. Motivated by the possibility of observing photoluminescence and electron paramagnetic resonance from the same species located within a fullerene molecule, we initiated an EPR study of Er 3+ in ErSc2N@C80. Two orientations of the ErSc2N rotor within the C80 fullerene are observed in EPR, consistent with earlier studies using photoluminescence excitation (PLE) spectroscopy. For some crystal field orientations, electron spin relaxation is driven by an Orbach process via the first excited electronic state of the 4 I 15/2 multiplet. We observe a change in the relative populations of the two ErSc2N configurations upon the application of 532 nm illuminations, and are thus able to switch the majority cage symmetry. This photoisomerisation, observable by both EPR and PLE, is metastable, lasting many hours at 20 K.
Optical properties of Er 3+ in fullerenes and in β-PbF 2 single-crystals
Optical Materials, 2009
With the aim of providing a thorough description of the optical properties of Er3+-doped endohedral fullerenes, we studied their characteristics in the light of those of well-known Er3+-doped β-PbF2 single-crystals. Various Er3+-doped endohedral fullerenes were considered: Er2C2@C82, where the Er2C2 group is encapsulated inside a cage of 82 carbon atoms and the Er3−xScxN@C80 (x = 0, 1 and 2) family, where the Er3N, Er2ScN and ErSc2N clusters are trapped in a 80 carbon atom cage. In this article, we discuss the absorption and photoluminescence of trivalent erbium ions in fullerenes and in β-PbF2 crystals. The extinction coefficient of Er3N@C80 was found to be 4.8 (±0.5) × 103 mol/l−1 cm−1 at 540 nm, due to the C80 cage absorbance. Even in a saturated fullerene solution, the absorption of Er3+ encapsulated inside a C80 cage cannot be observed at room temperature. We suggest that this is due to an insufficient number of Er3+ ions in the solution and their low absorption cross-section. Low temperature photoluminescence measurements show that the line width of Er3+ in a carbon cage, dissolved in a polycrystalline solvent, is similar to the one of Er3+ in β-PbF2 single-crystals. The quantum efficiency of Er3+ at 1.5 μm in fullerenes is four orders of magnitude lower than that for Er3+ in crystals, due to very efficient non-radiative decay processes. Molecular vibrations of the cage might be responsible for those rapid non-radiative de-excitations.
Measurement of Pair Interactions and 1.5 μm Emission from Er3+ Ions in a C82 Fullerene Cage
Physical Review Letters, 1997
Erbium ions encapsulated in the metallofullerene Er 2 @C 82 emit near infrared fluorescence about 1.5 mm, typical for 4 I 13͞2 ! 4 I 15͞2 transitions of Er 31. The similarity of spectra measured in glassy and polycrystalline media at 1.6 K, and the very narrow inhomogeneous linewidth ͑,1 cm 21 ͒, show that the fullerene cage provides a locally ordered environment for the two erbium ions, well isolated from the host medium. Spectral fine-structure is observed with line splittings of ϳ10 cm 21. It is proposed that these splittings are dominated by exchange interaction between the two Er 31 ions involving a novel superexchange pathway through the C 82 cage. [S0031-9007(97)03775-7]
PL, magneto-PL and PLE of the trimetallic nitride template fullerene Er3N@C80
physica status solidi (b), 2006
Er 3 N@C 80 exhibits sharp optical emission lines in the near-infrared attributed to fluorescence from the Er 3+ ion. Here we demonstrate that high magnetic fields cause this spectrum to split, corresponding to transitions from the lowest field-split Kramers doublet of the 4 I 13/2 manifold to the four lowest field-split levels of the 4 I 15/2 manifold. The internal structure of these fullerenes can be spatially aligned with a preferred orientation under high magnetic field; the effect of alignment is to reduce the broadening associated with the isotropic spatial averaging characteristic of powder or frozen-solution spectra. Using a tunable 1.5 µm laser, we directly observe non-cage-mediated optical interactions with the Er 3+ ion. This spectroscopic method provides the opportunity to map the energy level structure of the incarcerated ion and to coherently control its quantum state. These qualities suggest that rare-earth endohedral fullerenes have characteristics that could be employed as a readout pathway for fullerene-based quantum information processing.
Direct optical excitation of a fullerene-incarcerated metal ion
Chemical Physics Letters, 2006
The endohedral fullerene Er3N@C80 shows characteristic 1.5 µm photoluminescence at cryogenic temperatures associated with radiative relaxation from the crystal-field split Er 3+ 4 I 13/2 manifold to the 4 I 15/2 manifold. Previous observations of this luminescence were carried out by photoexcitation of the fullerene cage states leading to relaxation via the ionic states. We present direct non-cagemediated optical interaction with the erbium ion. We have used this interaction to complete a photoluminescence-excitation map of the Er 3+ 4 I 13/2 manifold. This ability to interact directly with the states of an incarcerated ion suggests the possibility of coherently manipulating fullerene qubit states with light.
Electron paramagnetic resonance study of ErSc2NC80
2010
We present an electron paramagnetic resonance (EPR) study of ErSc2N@C80 fullerene in which there are two Er3+ sites corresponding to two different configurations of the ErSc2N cluster inside the C80 cage. For each configuration, the EPR spectrum is characterized by a strong anisotropy of the g factors (gx,y = 2.9, gz = 13.0 and gx,y = 5.3, gz = 10.9). Illumination within the cage absorption range (<600 nm) induces a rearrangement of the ErSc2N cluster inside the cage. We follow the temporal dependence of this rearrangement phenomenologically under various conditions.
Electronic structure of undoped and doped fullerenes
Synthetic Metals, 1993
The electronic structure of C60 has been studied by electron energyloss spectroscopy (EELS) in transmission, and by high resolution photoemission (PES) studies. Information on the occupied and unoccupied lr, ~*, o and o* band structure is obtained by photoemission and Cls absorption EELS measurements, respectively. In addition, the dielectric function of undoped C6O~ as obtained from EELS measurements, show a clear gap of ~ 2eV and several ~vell pronounced ~->~* transitions. Upon doping with Li, Na, K, Rb, Cs and Ca, the filling of the lowest unoccupied molecular orbital (LUMO) band has been probed by both PES and EELS. For doping with divalent Ca, in addition the LUMO+I band gets partially filled. Strong non-rigid-band behaviour is observed. The results are compared with theoretical calculations.
Studies of fullerenes by the excitation, emission, and scattering of electrons
Journal of Electron Spectroscopy and Related Phenomena, 1999
This paper presents an overview of how electron spectroscopies have contributed to advances in fullerene research. In particular, we illustrate the vital role these techniques have played in improving our understanding of the importance of strong electronic correlation and of electron-phonon coupling in these materials, in the derivation of electron hopping rates, in providing a direct determination of charge transfer and hybridisation in both fullerene salts and adsorbed fullerenes and in determining the optical gap of these systems. We discuss systems of increasing complexity, starting with C in the gas phase 60 and in the solid state, and moving on to C salts and to C adsorbed on surfaces. Finally we look at both higher fullerenes 60 60 and fullerenes with a heteroatom either on or inside the cage.
Fullerenes in the highly excited state
Applied Physics A Solids and Surfaces, 1993
Under high intensity illumination, the optical and electronic properties of fullerenes are seen to undergo dramatic, nonlinear changes. The photoluminescence emission is seen to increase with approximately the third power of the input intensity above an apparent threshold intensity. Associated with this nonlinear increase is the emergence of a long lifetime emission component and a redshifting of the emission spectrum. Investigations of the photo-transport properties associate the observed behaviour with a phase transition in the highly excited state. Above an intensity which coincides with the onset of the nonlinear emission, the photoconductive response increases with approximately the cube of the input power. In the highly excited state, the photoconductive response becomes relatively temperature independent compared to the thermally activated behaviour observed at low intensities. The characteristics of the temperature dependence are associated with a high electron mobility phase in the highly excited state and therefore an optically driven insulator to metal transition is proposed as a description of the observed phenomena.