Hybridized quadrupole-dipole exciton effects in a ${\mathrm{Cu}}_{2}\mathrm{O}$-organic heterostructure

Hybridized quadrupole-dipole exciton effects in a ${Cu}_{2} O$ -organic heterostructure

Oleksiy Roslyak and Joseph L. Birman

Phys. Rev. B 75, 245309 – Published 6 June 2007

Abstract

In the present work, we discuss resonant hybridization of the $1 S$ quadrupole Wannier-Mott exciton (WE) in a ${Cu}_{2} O$ quantum well with the Frenkel dipole exciton in an adjacent layer of organic DCM2:CA:PA. The coupling between excitons is due to interaction between the gradient of electric field induced by the DCM2 Frenkel exciton (FE) and the quadrupole moment of the $1 S$ transition in the cuprous oxide. The specific choice of the organic allows us to use the mechanism of “solid state solvation” [C. Madigan and V. Bulovic, Phys. Rev. Lett. 91, 247403 (2003)] to dynamically tune the WE and FE into resonance for $\approx 3.3 ns$ (comparable with the big lifetime of the WE) of the “slow” phase of the solvation. The quadrupole-dipole hybrid utilizes the big oscillator strength of the FE, along with the big lifetime of the quadrupole exciton, unlike dipole-dipole hybrid exciton which utilizes the big oscillator strength of the FE and big radius of the dipole allowed WE. Due to the strong spatial dispersion and big mass of the quadrupole WE, the hybridization is not masked by the kinetic energy or the radiative broadening. The lower branch of the hybrid dispersion exhibits a pronounced minimum and may be used in applications. Also, we investigate and report noticeable change in the coupling due to an induced “Stark effect” from the strong local electric field of the FE. We investigated the fine energy structure of the quantum well confined ortho and para excitons in cuprous oxide.

Received 2 January 2007

DOI:https://doi.org/10.1103/PhysRevB.75.245309

Authors & Affiliations

Oleksiy Roslyak and Joseph L. Birman

Physics Department, The City College, CUNY, Convent Avenue at 138 Street, New York, New York 10031, USA

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Vol. 75, Iss. 24 — 15 June 2007

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Figure 1
Schematic representation of a possible experimental setup to produce quadrupole-dipole excitons. Here, the inorganic ${Cu}_{2} O$ quantum well provides the Wannier-Mott $1 S$ quadrupole exciton with the binding energy of $143 meV$ (for details, see Sec. 3). Two pumping photons $ℏ ω \approx E_{DCM 2}, E_{1 S}$ generate the hybrid signal from the upper $E_{u}$ and lower $E_{l}$ branches. The DCM2 part of the organic “solid state solute” provides the dipole allowed Frenkel exciton; the PS host prevents wave function overlapping between organic and inorganic excitons; CA under proper concentration allows tuning of the excitons into resonance. Due to the comparable lifetimes of both types of exciton, the system utilizes the strong spatial dispersion of the quadrupole exciton and big oscillator strength of the organic.Reuse & Permissions
Figure 2
The solid line shows the modified energy of the $1 S$ exciton as a function of the Bohr radius (Å) and variational parameter $λ$ due to the confinement effect; the dotted line shows the same function with the central cell correction not taken into account.Reuse & Permissions
Figure 3
(Color online) For numerical estimation of the confined quadrupole Bohr radius as an approximation, we took $a_{B}$ to be the bulk Bohr radius of $5.1 Å$ . So the “correction” equation [Eq. (7)] becomes a function of only one parameter $λ$ , and so does the binding energy [Eq. (6)].Reuse & Permissions
Figure 4
Schematic of dynamic tuning of Frenkel and $1 S$ quadrupole Wannier excitons by means of solid state solvation redshift effect. Following (1) photon absorption in DCM2, there are distinct dynamic phases: (2) fast adjustment of the electronic configuration in DCM2 due to interaction with polar CA molecules within the time frame of picoseconds, $τ_{f}$ ; (3) slow self-adjustment of DCM2 and CA molecules with $τ_{s} \approx 3.3 ns$ ; (4) absorption of second yellow photon delayed by $δ τ \approx τ_{s} - τ_{1 S}$ by ${Cu}_{2} O$ confined $1 S$ quadrupole exciton with lifetime $τ_{1 S} \approx 1.7 ns$ ; hybridization when detuning between this two types of exciton becomes smaller than the $k$ dependent coupling parameter; lifetimes of the hybrid are defined by $τ_{s}$ and $τ_{1 S}$ ; (5) phosphorescence due to the hybrid exciton recombination. (6) shows possible recombination of noninteracting excitons.Reuse & Permissions
Figure 5
The solid lines represent the upper and lower branches of the quadrupole-dipole hybrid dispersion when the coupling is calculated in the parabolic approximation and the induced Stark effect is taken into account; the dash lines correspond to the coupling parameter for different approximations: (1) infinite IQW and the induced Stark effect is neglected; (2) parabolic approximation; (3) infinite IQW with the induced Stark effect treated as a perturbation.Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Hybridized quadrupole-dipole exciton effects in a ${Cu}_{2} O$ -organic heterostructure

Oleksiy Roslyak and Joseph L. Birman

Phys. Rev. B 75, 245309 – Published 6 June 2007

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Physical Review B

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Hybridized quadrupole-dipole exciton effects in a Cu2O-organic heterostructure

Oleksiy Roslyak and Joseph L. Birman

Phys. Rev. B 75, 245309 – Published 6 June 2007

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Hybridized quadrupole-dipole exciton effects in a ${Cu}_{2} O$ -organic heterostructure