Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

The Journal of Chemical Physics

Theory of photon echoes from interacting impurities in crystals with inhomogeneously broadened absorption spectra

Roger F. Loring, Hans C. Andersen, M. D. Fayer

Published Dec 15, 1984• 23 citations
Publisher

Abstract

We present a theory of photon echoes from impurity molecules in mixed crystals that takes into account electronic interactions among impurity molecules and inhomogeneous broadening of the electronic absorption spectrum. The system is modeled as a collection of randomly placed interacting two level systems with a distribution of transition energies. The observable of the echo experiment is expanded in powers of the density of two level systems, and the first two terms of this expansion are calculated. A scaling argument suggests that the density expansion is rapidly convergent for concentrations of experimental interest, and the density expansion is used to construct a Padé approximant. At times comparable to or less than the inverse of the width of the inhomogeneous distribution of resonance frequencies, the time dependence of the signal is determined primarily by the interactions between the impurities and is independent of the inhomogeneous width. At longer times the inhomogeneity becomes significant and the echo signal displays a much weaker time dependence. We examine the effect of different microscopic models of inhomogeneous broadening on the echo observable. We demonstrate that the photon echo experiment can provide a sensitive probe of interactions between impurities in mixed crystals.

DOI
10.1063/1.447684

Related papers

Optical dephasing and photon echoes from energetically and substitutionally disordered crystals

Leslie J. Root, James L. Skinner

For a crystal with both diagonal disorder (inhomogeneous broadening) and substitutional disorder we have calculated the contribution to the photon echo decay due to purely electronic intersite interactions. We have considered the two important limiting cases of macroscopic and microscopic inhomogeneous broadening. In the case of macroscopic broadening we find that the optical dephasing rate constant 1/T2∼f J, where f is the fractional concentration of impurities and J is the nearest-neighbor intersite interaction in frequency units. This result is valid for f≪1. In the opposite limit of microscopic inhomogeneous broadening, we find that 1/T2∼f J2/δ̄, where δ̄ is the width in frequency units of the inhomogeneous distribution. This result is valid for arbitrary f, including f=1, and for J≪δ̄. In the case that f≪1 and J≪δ̄, 1/T2 is much smaller for microscopic broadening than for macroscopic broadening. We discuss our results in relation to several experiments on mixed molecular crystals and to an experiment on the stoichiometric material EuP5O14.

The Journal of Chemical Physics•Dec 15, 1984•36 citations

Inhomogeneous broadening in solids: Progress towards a microscopic understanding

James L. Skinner, Brian B. Laird, Leslie J. Root

Abstract Inhomogeneous broadening is often considered a nuisance in solid state spectroscopy, and the usual treatment of it is phenomenological. In fact, the inhomogeneous broadening of absorption spectra, coupled with a microscopic theory, can provide one with interesting information about the nature of disorder in different systems. More sophisticated experiments can provide more detailed information about disorder by probing certain correlations between energy levels. For example, flourescence line narrowing spectra of isolated impurities involve correlations among three different vibronic levels. Pressure effects on hole burning spectra probe correlations of impurity transition energies before and after the pressure change. For interacting impurity systems, photon echo experiments involve transition energy correlations between different impurities. Efforts to understand these effects within a microscopic framework are discussed.

Journal of Luminescence•Jan 1, 1990•16 citations

Frequency-dependent optical dephasing and the nature of inhomogeneous broadening in crystals

Leslie J. Root, James L. Skinner

We present a theory of frequency-dependent optical dephasing as measured by narrow-band photon-echo experiments. We consider a substitutionally disordered crystal with inhomogeneous broadening (diagonal disorder) and electronic interactions between occupied sites. We include the possibility of site-energy correlations. We find that the frequency dependence of the dephasing rate 1/${T}_{2}$ is very sensitive to the ratio \ensuremath{\xi}/a, where \ensuremath{\xi} is the correlation length and a is the lattice spacing. When \ensuremath{\xi}/a\ensuremath{\rightarrow}\ensuremath{\infty}, and there are macroscopic domains of resonant ions, 1/${T}_{2}$ becomes frequency independent. In the other limit when \ensuremath{\xi}/a\ensuremath{\rightarrow}0, and the site energies are uncorrelated (microscopic broadening), 1/${T}_{2}$ is proportional to the inhomogeneous line shape. We have compared our results to experiments by Macfarlane and Shelby on ${\mathrm{Y}}_{2}$${\mathrm{O}}_{3}$:${\mathrm{Eu}}^{3+}$ (2 at. %) and ${\mathrm{EuP}}_{5}$${\mathrm{O}}_{14}$. We find reasonable agreement with experiment when \ensuremath{\xi} is less than a few lattice sites. Thus, for these systems the model of microscopic broadening is more appropriate than that of macroscopic broadening.

Physical review. B, Condensed matter•Sep 15, 1985•25 citations

Theory of photon echoes from a pair of coupled two level systems: Impurity dimers and energy transfer in molecular crystals

James L. Skinner, Hans C. Andersen, M. D. Fayer

We present the theory of the photon echo and stimulated photon echo from a four level system that results from a pair of weakly coupled two level systems. This model describes an impurity dimer in a molecular crystal. We include the effect of relaxation processes, focusing on energy transfer between delocalized states. We find that both the photon and stimulated echoes contain information about static level splittings and dynamic energy transfer processes. Moreover, these observables show a dramatic dependence on the excitation power. We discuss implications of our results for recent experiments on concentration dependent dephasing of impurities in molecular crystals. Our analysis casts considerable doubt on the intermolecular interaction interpretation of these experiments.

The Journal of Chemical Physics•Oct 1, 1981•37 citations

Photon echoes of polyatomic molecules in condensed phases

Yi Jing Yan, Shaul Mukamel

A theory of optical echo spectroscopies of large polyatomic molecules in condensed phases is developed. Using phase space correlation functions, we examine the interrelationships among the following optical measurements: ordinary photon echo, stimulated photon echo, accumulated photon echo, incoherent accumulated photon echo, and pump–probe absorption. Conditions for the elimination of inhomogeneous broadening in these experiments are specified. A multimode Brownian oscillator model is used to account for high frequency molecular vibrations, as well as solvent modes, and electronic dephasing processes. The effects of quantum beats, spectral diffusion, and homogeneous dephasing on the echo signals are studied and compared in detail with pump–probe and hole burning spectroscopy.

The Journal of Chemical Physics•Jan 1, 1991•172 citations

Intermolecular interaction dynamics and optical dephasing: Picosecond photon echo measurements in mixed molecular crystals

Donald E. Cooper, Radley W. Olson, M. D. Fayer

Picosecond optical coherence techniques are employed to study dynamical intermolecular interactions in low concentration mixed molecular crystals, i.e., pentacene in naphthalene at 1.4 K. A concentration-dependent broadening of the optical homogeneous line is observed. Stimulated photon echo measurements rule out excited state transport as the broadening mechanism. The photon echo results exhibit a linear concentration dependence and a theory is proposed that accounts for the broadening in terms of phonon-induced fluctuations in guest–guest dipole–dipole interactions. Detailed considerations indicate that the system is best described in terms of localized excitations rather than delocalized impurity band states. In the low concentration limit, there is additional broadening of the homogeneous line beyond that produced by the lifetime. A model is presented describing this broadening in terms of phonon-induced modulation of the guest–host van der Waals interactions, i.e., in terms of a fluctuating crystal shift.

The Journal of Chemical Physics•Feb 15, 1980•42 citations
We present a theory of photon echoes from impurity molecules in mixed crystals that takes into account electronic interactions among impurity molecules and inhomogeneous broadening of the electronic absorption spectrum. The system is modeled as a collection of randomly placed interacting two level systems with a distribution of transition energies. The observable of the echo experiment is expanded in powers of the density of two level systems, and the first two terms of this expansion are calculated. A scaling argument suggests that the density expansion is rapidly convergent for concentrations of experimental interest, and the density expansion is used to construct a Padé approximant. At times comparable to or less than the inverse of the width of the inhomogeneous distribution of resonance frequencies, the time dependence of the signal is determined primarily by the interactions between the impurities and is independent of the inhomogeneous width. At longer times the inhomogeneity becomes significant and the echo signal displays a much weaker time dependence. We examine the effect of different microscopic models of inhomogeneous broadening on the echo observable. We demonstrate that the photon echo experiment can provide a sensitive probe of interactions between impurities in mixed crystals.
For a crystal with both diagonal disorder (inhomogeneous broadening) and substitutional disorder we have calculated the contribution to the photon echo decay due to purely electronic intersite interactions. We have considered the two important limiting cases of macroscopic and microscopic inhomogeneous broadening. In the case of macroscopic broadening we find that the optical dephasing rate constant 1/T2∼f J, where f is the fractional concentration of impurities and J is the nearest-neighbor intersite interaction in frequency units. This result is valid for f≪1. In the opposite limit of microscopic inhomogeneous broadening, we find that 1/T2∼f J2/δ̄, where δ̄ is the width in frequency units of the inhomogeneous distribution. This result is valid for arbitrary f, including f=1, and for J≪δ̄. In the case that f≪1 and J≪δ̄, 1/T2 is much smaller for microscopic broadening than for macroscopic broadening. We discuss our results in relation to several experiments on mixed molecular crystals and to an experiment on the stoichiometric material EuP5O14.
Abstract Inhomogeneous broadening is often considered a nuisance in solid state spectroscopy, and the usual treatment of it is phenomenological. In fact, the inhomogeneous broadening of absorption spectra, coupled with a microscopic theory, can provide one with interesting information about the nature of disorder in different systems. More sophisticated experiments can provide more detailed information about disorder by probing certain correlations between energy levels. For example, flourescence line narrowing spectra of isolated impurities involve correlations among three different vibronic levels. Pressure effects on hole burning spectra probe correlations of impurity transition energies before and after the pressure change. For interacting impurity systems, photon echo experiments involve transition energy correlations between different impurities. Efforts to understand these effects within a microscopic framework are discussed.
We present a theory of frequency-dependent optical dephasing as measured by narrow-band photon-echo experiments. We consider a substitutionally disordered crystal with inhomogeneous broadening (diagonal disorder) and electronic interactions between occupied sites. We include the possibility of site-energy correlations. We find that the frequency dependence of the dephasing rate 1/T2{T}_{2}T2​ is very sensitive to the ratio \ensuremath{\xi}/a, where \ensuremath{\xi} is the correlation length and a is the lattice spacing. When \ensuremath{\xi}/a\ensuremath{\rightarrow}\ensuremath{\infty}, and there are macroscopic domains of resonant ions, 1/T2{T}_{2}T2​ becomes frequency independent. In the other limit when \ensuremath{\xi}/a\ensuremath{\rightarrow}0, and the site energies are uncorrelated (microscopic broadening), 1/T2{T}_{2}T2​ is proportional to the inhomogeneous line shape. We have compared our results to experiments by Macfarlane and Shelby on Y2{\mathrm{Y}}_{2}Y2​O3{\mathrm{O}}_{3}O3​:Eu3+{\mathrm{Eu}}^{3+}Eu3+ (2 at. %) and EuP5{\mathrm{EuP}}_{5}EuP5​O14{\mathrm{O}}_{14}O14​. We find reasonable agreement with experiment when \ensuremath{\xi} is less than a few lattice sites. Thus, for these systems the model of microscopic broadening is more appropriate than that of macroscopic broadening.
We present the theory of the photon echo and stimulated photon echo from a four level system that results from a pair of weakly coupled two level systems. This model describes an impurity dimer in a molecular crystal. We include the effect of relaxation processes, focusing on energy transfer between delocalized states. We find that both the photon and stimulated echoes contain information about static level splittings and dynamic energy transfer processes. Moreover, these observables show a dramatic dependence on the excitation power. We discuss implications of our results for recent experiments on concentration dependent dephasing of impurities in molecular crystals. Our analysis casts considerable doubt on the intermolecular interaction interpretation of these experiments.
A theory of optical echo spectroscopies of large polyatomic molecules in condensed phases is developed. Using phase space correlation functions, we examine the interrelationships among the following optical measurements: ordinary photon echo, stimulated photon echo, accumulated photon echo, incoherent accumulated photon echo, and pump–probe absorption. Conditions for the elimination of inhomogeneous broadening in these experiments are specified. A multimode Brownian oscillator model is used to account for high frequency molecular vibrations, as well as solvent modes, and electronic dephasing processes. The effects of quantum beats, spectral diffusion, and homogeneous dephasing on the echo signals are studied and compared in detail with pump–probe and hole burning spectroscopy.
Picosecond optical coherence techniques are employed to study dynamical intermolecular interactions in low concentration mixed molecular crystals, i.e., pentacene in naphthalene at 1.4 K. A concentration-dependent broadening of the optical homogeneous line is observed. Stimulated photon echo measurements rule out excited state transport as the broadening mechanism. The photon echo results exhibit a linear concentration dependence and a theory is proposed that accounts for the broadening in terms of phonon-induced fluctuations in guest–guest dipole–dipole interactions. Detailed considerations indicate that the system is best described in terms of localized excitations rather than delocalized impurity band states. In the low concentration limit, there is additional broadening of the homogeneous line beyond that produced by the lifetime. A model is presented describing this broadening in terms of phonon-induced modulation of the guest–host van der Waals interactions, i.e., in terms of a fluctuating crystal shift.