Persistent Spectral Hole Burning Spectroscopy Research Articles

Longitudinal optical phonons in the excited state of CuBr quantum dots

The size dependence of the longitudinal optical (LO) phonons in the excited state of CuBr quantum dots (QD's) in glass and NaBr crystals in the intermediate confinement regime was studied by means of persistent spectral hole burning spectroscopy. The phonon-exciton coupled states were clearly observed at a photon energy of about 2.993 eV when the LO phonon energy is close to the energy difference between the ground $1S$ and excited $1P$ states of CuBr QD's in glass. The energies of the LO phonons observed in smaller CuBr QD's in glass and NaBr crystals were determined to be about 18.6 and 17.6 meV, respectively, which are smaller than that of LO phonons in the bulk CuBr material. The energy softening of the LO phonons was explained in terms of the phonon renormalization.

Exciton-phonon coupled states in CuCl quantum cubes

The size dependence of excitonic states and vibrational modes in CuCl cubic quantum dots embedded in NaCl crystals was studied by means of site-selective persistent spectral hole burning spectroscopy. It is shown that the interaction of the longitudinal optical (LO) phonon with the exciton results in the formation of coupled exciton-phonon modes when the energy of the LO phonon approaches the energy spacings between the ground and excited states of the exciton. The energy anticrossings of the LO phonon modes with two higher optically allowed excited states of the exciton in CuCl QD's were clearly observed at confinement energies of about 10 and 6 meV, respectively. In addition, the linewidth of the LO phonon sideband in CuCl QD's in NaCl crystals was found to increase abruptly from 0.3 meV to about 1.2 meV at a confinement energy of about 23 meV, which appears to result from the exciton-phonon mixing of the LO phonon mode with the first excited state of the exciton. The experimental results are qualitatively understood by the LO phonon renormalization theory.

Effect of sodium ions on persistent spectral hole burning in Pr 3+-doped silicate glasses

Persistent spectral hole-burning spectroscopy has been carried out for the 3 H 4 → 1 D 2 transition of Pr 3+ in (100− x)SiO 2· xNa 2O glasses with x=10, 20, 33.3 and 45 in order to examine the effect of Na 2O content on the homogeneous width and hole-burning efficiency. The homogeneous width shows a nearly T-linear dependence below about 10 K irrespective of glass composition, which is characteristic of optical dephasing due to dynamical process associated with low-energy excitation modes in glasses. Both the homogeneous width and hole-burning efficiency increase with an increase in Na 2O content at 4.2 K. These observations are interpreted based on the coupling of the 3H 4– 1D 2 transition of Pr 3+ to the low-energy excitation modes in sodium silicate glasses.

Size dependence of confined acoustic phonons in CuCl nanocrystals

Persistent spectral hole burning spectroscopy was used to study the size dependence of the confined acoustic phonons in CuCl nanocrystals embedded in silicate glass, NaCl, and KCl. It is found that the energies of the confined acoustic phonons in the nanocrystals in glass and KCl are almost the same, but twice larger than those in NaCl, which were obtained from the Stokes-side acoustic phonon holes with the same excitation energies. The confined acoustic phonons in the nanocrystals in glass and KCl can be well explained in terms of the lowest-frequency vibrational modes calculated on a sphere model with a free boundary condition. However, the energies of the confined acoustic phonons in the nanocrystals in NaCl are lower than the frequencies of the lowest-frequency vibrational modes predicted by a cube model with a free boundary condition. This observation shows that the energies of the confined acoustic phonons in CuCl nanocrystals depend on the size, the shape, and the boundary condition of the nanocrystals.

Low-temperature relaxation of polymers around doped dyes studied by persistent spectral hole burning

Persistent spectral hole burning spectroscopy is applied to evaluate the low-temperature relaxation around the dye molecules doped in several types of polymers. The doped dye is tetraphenylporphine, and the measured polymers are vinyl polymers and main chain aromatic polymers. The changes of microscopic environments around the dye are evaluated from the changes in the hole profiles during temperature cycling experiments. The relaxation behavior of the polymers is discussed in relation to their chemical structures. (C) 1999 John Wiley & Sons, Inc.

Photoinduced electron transfer process probed by persistent spectral hole burning spectroscopy. The effect of the acceptor on non-photochemical hole burning

We studied the photoinduced electron transfer process at low temperatures by suing persistent spectral hole burning spectroscopy. The efficiency of non-photochemical hole burning for zinc tetraphenylporphine (ZnTPP) and zinc phthalocyanine decreased in the presence of electron acceptors. This is attributed to fast electron transfer and charge recombination reactions. The rate constant of the electron transfer from ZnTPP to the naphthoquinone group which is linked with ZnTPP via a methylene chain (n = 6) at 4.2 K was estimated to be 9.4 × 1010 s−1.

Observation of confined acoustic phonons in semiconductor nanocrystals by means of the persistent spectral hole-burning spectroscopy

We report on observation of confined acoustic phonons in CuCl nanocrystals by means of a site-selective nanosecond pump-and-probe method. The nanocrystal-size-dependent energy intervals between the zero-phonon line and phonon side bands in the hole-burning spectra coincide with the calculated energies of confined acoustic phonons in nanometer-size elastic spheres. We conclude that the phonon side bands are due to confined acoustic phonons in CuCl nanocrystals. The observed confined acoustic phonon mode depends on the elastic constants of the surrounding matrices, glass and NaCl. The persistent spectral hole-burning phenomenon serves as the observation of the zero-phonon line and phonon side bands.

Relationship between Spectral Hole Burning and Stokes Shift of Organic Dyes in Polymer Systems

Abstract Several organic dyes were studied both by fluorescence spectroscopy and by persistent spectral hole burning spectroscopy. The chromophores realizing spectral hole formation at 20 K have small Stokes shift approximately less than 103 cm−1. It ascertains that the small Stokes shift related to the existence of appreciable zero-phonon line would be a requisite for the spectral hole formation of the chromophore. The realization of hole formation by using poly(vinyl alcohol) or photoreactive matrices for the chromophores which have appreciable zero-phonon line but don’t undergo light-induced chemical or conformational change is also discussed.