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Observation of strong exciton–photon coupling in an organic microcavity in transmission and photoluminescence
Journal of Luminescence 94–95 (2001) 821–826
Observation of strong exciton–photon coupling in an organic microcavity in transmission and photoluminescence P. Schouwinka,*, H. von Berlepschb, L. D.ahnec, R.F. Mahrta,d b
a Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany Freie Universitat . Berlin, Forschungszentrum fur . Elektronenmikroskopie, Fabeckstr. 36a, 14195 Berlin, Germany c Max Planck Institute of Colloids and Interfaces, Am Muhlenberg 1, 14476 Golm/Potsdam, Germany . d IBM Research, Zurich Research Laboratory, Saumerstrasse 4, 8803 Ruschlikon, Switzerland . .
Abstract An optical organic semiconductor microcavity in the strong coupling regime containing J-aggregates (1,10 -diethyl2,20 -cyanine (PIC)) as optically active material has been investigated. Stable thin layers of homogeneously distributed aggregates were prepared by spin-coating of a specific salt of this dye [(PIC+)2B10H2 10 ] without the need of a polymer matrix. Transmission and photoluminescence measurements reveal an anticrossing that is typical for the strong coupling regime. Compared with inorganic semiconductors, a large Rabi splitting of approximately 25 meV was observed in the transmission and photoluminescence measurements. r 2001 Elsevier Science B.V. All rights reserved. Keywords: Rabi splitting; Organic microcavities; J-aggregate
1. Introduction The understanding and control of interactions between an electromagnetic field and the optical transition of a material is of both fundamental and technological interest. Semiconductor microcavities are a very successful tool to alter the exciton– photon interaction. Two different regimes of interaction can be distinguished: the weak coupling regime and strong coupling regime. In the weak coupling regime, a spectrally very pure and strongly forward-directed emission is observed. *Corresponding author. Tel.: +49-6131-379-485; fax: +496131-379-100. E-mail address: [email protected] (P. Schouwink).
The strong coupling regime, however, manifests itself in an anticrossing of two coupled modes. These new cavity polariton modes are an admixture of the cavity photon modes and the optical transition of the material. The spontaneous emission is no longer an irreversible process, but an oscillation (Rabi oscillation) with decreasing amplitude. The closest energetic proximity of these two modes occurs at resonance of the cavity photon mode with the energy of the optical transition of the material inside the cavity and is called the vacuum Rabi splitting energy. The first observation of the strong coupling regime was with atoms within an optical microcavity [1] in the early 1980s. Inorganic quantum wells made it possible to achieve the strong coupling regime within optical inorganic
0022-2313/01/$ - see front matter r 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 2 3 1 3 ( 0 1 ) 0 0 3 7 5 - 1
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semiconductor microcavities [2] in the early 1990s. It was not until 1998, since Lidzey et al. could demonstrate the strong coupling regime within an optical organic ‘‘semiconductor’’ microcavity [3– 7]. However, up to now, only little is known [4] about the photoluminescence in the strong coupling regime of optical organic ‘‘semiconductor’’ microcavities. The strong coupling regime can be achieved in high-quality optical microcavities with an optically active material having an exciton with high oscillator strength combined with a small linewidth. J-aggregates fulfill these requirements [4,8]. In our study, the cationic dye 1,10 -diethyl-2,20 cyanine (PIC) which can form J-aggregates, was used as optically active organic material. Stable thin layers of homogeneously distributed PIC aggregates without any matrix could be prepared by spin-coating of PIC-decahydro-closo-decaborate salt [9]. A thin layer of homogeneously distributed J-aggregates was hence fabricated inside a planar l=2-microcavity.
2. Experimental Optical organic semiconductor microcavities (see inset Fig. 2a) were prepared in the following
way: On top of a dielectric mirror consisting of nine double layers of SiO2 (n ¼ 1:457) and TaO2 (n ¼ 2:03), a thin film of the dye PIC (see inset of Fig. 1) was prepared by means of spin-coating a saturated solution of the specific dye salt 1,10 diethyl-2,20 -cyanine decahydro-closo-decaborate [(PIC+)2B10H2 10 ] in a 2 : 1 mixture (weight ratio) of acetonitrile and ethylene dichloride. On applying a high acceleration of the spinning table (up to 3000 rpm in 1.6 s), layers with a typical thickness of 50 nm could be prepared from the saturated dye solution. Prior to spin-coating, the wettability of the mirrors was improved by a plasma treatment with ordinary air. Then, further, a 120 nm thick SiOx layer was evaporated at a background pressure of o2 105 mbar. The evaporation rate ( The thickness of the film was monitored was 2 A/s. by a quartz crystal oscillator. Finally, a 150 nm thick silver layer was evaporated as top mirror ( at a background with an evaporation rate of 5 A/s 5 pressure of o2 10 mbar. Different detunings between the photon mode of the cavity and the optical transition of the material inside the cavity can be achieved by applying different angles between the main cavity axis and the measurement direction [10]. The transmission measurements were taken using a 100 W halogen lamp as light source. For
Fig. 1. Absorption and PL spectrum of a thin film of the 1,10 -diethyl-2,20 -cyanine decahydro-closo-decaborate at 4.2 K. Inset: molecular structure of PIC.
P. Schouwink et al. / Journal of Luminescence 94–95 (2001) 821–826
the photoluminescence (PL) measurements, the sample was excited with the 532 nm line of a diode CW laser. The transmitted and emitted light were detected by a 0.3 m monochromator with a 1200 grooves/mm grating coupled to a CCDdetector. The samples were kept in a static flow cryostat at a temperature of 4.2 K during the measurements.
3. Results and discussion The absorption spectrum of the thin PIC film (Fig. 1) shows the characteristics of a J-aggregate with a narrow absorption band at 2.179 eV having a full-width at half-maximum (FWHM) of 41 meV. This is assigned to the exciton of the Jaggregate. Additionally absorption bands can be observed. The absorption spectrum is in agreement with absorption spectra of different PIC-salts (PIC-I, PIC-Cl, PIC-Br) in a polymer matrix [11– 13]. However, a shift to lower energies is visible due to the low temperature. (The low temperature PL spectrum of thin PIC-film is displayed in Fig. 1). Besides a sharp emission band at 2.169 eV, a broad emission band peaked at 1.979 eV is observed. The stokes shift is just 10 meV. We assign the sharp emission to the J-aggregate excition and the broad band emission to an emission from defect states [13]. Fig. 2a shows the low-temperature transmission spectra depending on the detuning between the exciton energy and the cavity photon mode. The exciton energy of the J-aggregate is defined as 0 meV. Far off resonance, at small angles (low energies), only one peak, corresponding to the cavity photon mode, can be observed. Tuning the photon mode energy to the energy of the exciton of the J-aggregate, an additional peak at higher energy appears and gains in integrated intensity. Between 291 and 301, the two peaks reach equal integrated intensities (see the arrow in Fig. 2a). Tuning to even higher angles, and hence higher energies of the cavity photon mode, a positive detuning is achieved. Here, the low-energy peak decreases in integrated intensity and finally disappears at around 341, whereas the high-energy
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peak gains integrated intensity. The behavior described above is typical for the strong coupling regime in microcavities. At around 0 meV of detuning, the interaction between the cavity photon modes and the optical transition of the J-aggregate becomes large compared with the leakage channels. An emitted photon is reabsorbed before it escapes from the cavity. This leads to a mixing of the photon and exciton states. Two new eigenstates described as an admixture of the photon and exciton states are created. On resonance, at 0 meV detuning, both peaks have halfphoton and half-exciton character. A plot of the peak position depending on the cavity detuning (Fig. 3) shows a clear anticrossing of the two branches typical for the strong coupling regime. The closest proximity between the two branches (at 0 meV detuning), the so-called Rabi-splitting energy, is a measure of the interaction between the cavity photon mode and the optical transition. Here, the Rabi splitting energy is slightly bigger than 25 meV. In the weak coupling regime, the density of photon modes inside the cavity is different from the situation in the vacuum. Only a few photon modes are allowed due to the resonance conditions given by the restricted geometry. All other photon modes are suppressed. The cavity couples the optical transition of the material with the resonant photon modes. Therefore, photons have to be emitted into these allowed modes. Due to this coupling, a broad emission spectrum of the optically active material in the vacuum is reduced to the small spectral width of the allowed photon modes. In the strong coupling regime, however, the situation is different. Here, the simplest picture of the two coupled modes is a photon, that creates an exciton, that afterwards emits a photon. This process keeps on in a cyclic fashioned way [14]. Fig. 2b shows the low temperature PL spectra depending on the detuning between the exciton energy and the cavity photon mode. A scenario similar to the transmission spectra is observed. The peak position of the bands in the PL-spectra in the strong coupling-regime just resemble the dispersion curve for the transmission measurements in the strong coupling regime [10,15,16]. In Fig. 3, the peak position of the PL bands are plotted together
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Fig. 3. Peak position of the high-energy (circles) and low-energy (squares) bands for transmission (solid symbols) and PL (open symbols) spectra depending on the cavity detuning. The energy of the exciton of the J-aggregate is set as 0 meV. The dotted lines are a guide to the eyes. The two branches show a clear anticrossing behavior with a Rabi splitting of approximately 25 meV for the transmission measurement as well as for the PL measurement.
with the peak positions of the transmission bands. The peak positions of the two bands in transmission and PL are in good agreement. We assign this to a radiative emission from the two bands in the transmission measurements. Further measurements are under way to prove if the photoluminescence is thermalized, in that whether it follows the absorption spectra weighted by a Boltzmann population factor as it has been observed for
b—————————————————————————— Fig. 2. (a) Transmission spectra of the optical organic semiconductor microcavity at different angles between the main cavity axis and the measurement direction corresponding to different cavity detunings. The energy of the exciton of the Jaggregate is defined as 0 meV. Small angles correspond to large negative detunings, large angles to a large positive detuning. The arrow indicates the 0 meV detuning between 291 and 301. Inset: structure of the optical organic semiconductor microcavities used in this study. (b) PL spectra of the optical organic semiconductor microcavity at different angles between the main cavity axis and the measurement direction corresponding to different cavity detunings. The energy of the exciton of the Jaggregate is defined as 0 meV. Small angles correspond to large negative detunings, large angles to a large positive detuning. The arrow indicates the 0 meV detuning between 291 and 301.
semiconductor microcavities in the strong coupling regime [16]. 4. Conclusions High-quality optical organic semiconductor microcavities with a thin layer of homogeneously distributed J-aggregates of PIC as optically active material were prepared. The anticrossing behavior typical for the strong coupling regime in optical semiconductor microcavities has been observed in the transmission and photoluminescence measurements. The Rabi splitting in both cases is approximately 25 meV. Acknowledgements We thank A. Plekhanov and V.V. Shelkovnikov (Sibirian Branch of the Academy of Science, Novosibirsk, Russia) for providing the PIC material. The work was supported by the Deutsche Forschungsgemeinschaft (DA 287/5-1), Volkswagen Stiftung, Fond der Chemischen Industrie and the INTAS foundation (INTAS No. 97-10434).
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References [1] S. Haroche, D. Kleppner, Phys. Today 42 (1989) 24. [2] C. Weisbuch, M. Nishioka, A. Ishikawa, Y. Arakawa, Phys. Rev. Lett. 69 (1992) 3314. [3] D.G. Lidzey, D.D.C. Bradley, M.S. Skolnick, T. Virgili, S. Walker, D.M. Whittacker, Nature 395 (1998) 53. [4] D.G. Lidzey, D.D.C. Bradley, T. Virgili, A. Armitage, M.S. Skolnick, Phys. Rev. Lett. 82 (16) (1999) 3316. [5] D.G. Lidzey, T. Virgili, D.D.C. Bradley, M.S. Skolnick, S. Walker, D.M. Whittaker, Opt. Mater. 12 (1999) 243. [6] M.S. Skolnick, V.N. Astratov, D.M. Whittaker, A. Armitage, M. Eman-Ismael, R.M. Stevenson, J.J. Baumberg, J.S. Roberts, D.G. Lidzey, T. Virgili, D.D.C. Bradley, J. Lumin. 87–89 (2000) 25. [7] D.G. Lidzey, D.D.C. Bradley, A. Armitage, S. Walker, M.S. Skolnick, Science 288 (2000) 1620. . [8] H.v. Berlepsch, S. Moller, L. D.ahne, J. Phys. Chem. B 106 (2001) 5689.
[9] T.N. Gerasimova, N.A. Orlova, V.V. Shelkovnikov, Z.M. Ivanova, R.V. Morkov, A. Plekhanov, T.M. Polynskaya, V.V., Chem. Sustainable Dev. 8 (2000) 109. [10] R. Houdre, C. Weisbuch, R.P. Stanley, U. Oesterle, P. Pellandini, M. Ilegems, Phys. Rev. Lett. 73 (15) (1994) 2043. [11] D.A. Higgins, J. Kerimo, D.A. Vanden, Bout, P.F. Barbara, J. Am. Chem. Soc. 118 (1996) 4049. [12] T. Kobayashi, K. Misawa, J. Lumin. 72–74 (1997) 38. [13] M. Vacha, M. Furuki, T. Tani, J. Phys. Chem. B. 102 (1998) 1916. [14] V. Savona, L.C. Andreani, P. Schwendimann, A. Quattropani, Solid State Commun. 93 (1995) 733. [15] C. Weisbuch, R. Houdre, R.P. Stanley, in: H. Yokoyama, K. Ujihara (Eds.), Spontaneous Emission and Laser Oscillation in Microcavities, CRC, Boca Raton, 1995, p. 109. [16] R.P. Stanley, R. Houndre, C. Weisbuch, U. Oesterle, M. Ilegems, Phys. Rev. B 53 (16) (1996) 10 995.
Observation of strong exciton–photon coupling in an organic microcavity in transmission and photoluminescence P. Schouwinka,*, H. von Berlepschb, L. D.ahnec, R.F. Mahrta,d b
a Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany Freie Universitat . Berlin, Forschungszentrum fur . Elektronenmikroskopie, Fabeckstr. 36a, 14195 Berlin, Germany c Max Planck Institute of Colloids and Interfaces, Am Muhlenberg 1, 14476 Golm/Potsdam, Germany . d IBM Research, Zurich Research Laboratory, Saumerstrasse 4, 8803 Ruschlikon, Switzerland . .
Abstract An optical organic semiconductor microcavity in the strong coupling regime containing J-aggregates (1,10 -diethyl2,20 -cyanine (PIC)) as optically active material has been investigated. Stable thin layers of homogeneously distributed aggregates were prepared by spin-coating of a specific salt of this dye [(PIC+)2B10H2 10 ] without the need of a polymer matrix. Transmission and photoluminescence measurements reveal an anticrossing that is typical for the strong coupling regime. Compared with inorganic semiconductors, a large Rabi splitting of approximately 25 meV was observed in the transmission and photoluminescence measurements. r 2001 Elsevier Science B.V. All rights reserved. Keywords: Rabi splitting; Organic microcavities; J-aggregate
1. Introduction The understanding and control of interactions between an electromagnetic field and the optical transition of a material is of both fundamental and technological interest. Semiconductor microcavities are a very successful tool to alter the exciton– photon interaction. Two different regimes of interaction can be distinguished: the weak coupling regime and strong coupling regime. In the weak coupling regime, a spectrally very pure and strongly forward-directed emission is observed. *Corresponding author. Tel.: +49-6131-379-485; fax: +496131-379-100. E-mail address: [email protected] (P. Schouwink).
The strong coupling regime, however, manifests itself in an anticrossing of two coupled modes. These new cavity polariton modes are an admixture of the cavity photon modes and the optical transition of the material. The spontaneous emission is no longer an irreversible process, but an oscillation (Rabi oscillation) with decreasing amplitude. The closest energetic proximity of these two modes occurs at resonance of the cavity photon mode with the energy of the optical transition of the material inside the cavity and is called the vacuum Rabi splitting energy. The first observation of the strong coupling regime was with atoms within an optical microcavity [1] in the early 1980s. Inorganic quantum wells made it possible to achieve the strong coupling regime within optical inorganic
0022-2313/01/$ - see front matter r 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 2 3 1 3 ( 0 1 ) 0 0 3 7 5 - 1
822
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semiconductor microcavities [2] in the early 1990s. It was not until 1998, since Lidzey et al. could demonstrate the strong coupling regime within an optical organic ‘‘semiconductor’’ microcavity [3– 7]. However, up to now, only little is known [4] about the photoluminescence in the strong coupling regime of optical organic ‘‘semiconductor’’ microcavities. The strong coupling regime can be achieved in high-quality optical microcavities with an optically active material having an exciton with high oscillator strength combined with a small linewidth. J-aggregates fulfill these requirements [4,8]. In our study, the cationic dye 1,10 -diethyl-2,20 cyanine (PIC) which can form J-aggregates, was used as optically active organic material. Stable thin layers of homogeneously distributed PIC aggregates without any matrix could be prepared by spin-coating of PIC-decahydro-closo-decaborate salt [9]. A thin layer of homogeneously distributed J-aggregates was hence fabricated inside a planar l=2-microcavity.
2. Experimental Optical organic semiconductor microcavities (see inset Fig. 2a) were prepared in the following
way: On top of a dielectric mirror consisting of nine double layers of SiO2 (n ¼ 1:457) and TaO2 (n ¼ 2:03), a thin film of the dye PIC (see inset of Fig. 1) was prepared by means of spin-coating a saturated solution of the specific dye salt 1,10 diethyl-2,20 -cyanine decahydro-closo-decaborate [(PIC+)2B10H2 10 ] in a 2 : 1 mixture (weight ratio) of acetonitrile and ethylene dichloride. On applying a high acceleration of the spinning table (up to 3000 rpm in 1.6 s), layers with a typical thickness of 50 nm could be prepared from the saturated dye solution. Prior to spin-coating, the wettability of the mirrors was improved by a plasma treatment with ordinary air. Then, further, a 120 nm thick SiOx layer was evaporated at a background pressure of o2 105 mbar. The evaporation rate ( The thickness of the film was monitored was 2 A/s. by a quartz crystal oscillator. Finally, a 150 nm thick silver layer was evaporated as top mirror ( at a background with an evaporation rate of 5 A/s 5 pressure of o2 10 mbar. Different detunings between the photon mode of the cavity and the optical transition of the material inside the cavity can be achieved by applying different angles between the main cavity axis and the measurement direction [10]. The transmission measurements were taken using a 100 W halogen lamp as light source. For
Fig. 1. Absorption and PL spectrum of a thin film of the 1,10 -diethyl-2,20 -cyanine decahydro-closo-decaborate at 4.2 K. Inset: molecular structure of PIC.
P. Schouwink et al. / Journal of Luminescence 94–95 (2001) 821–826
the photoluminescence (PL) measurements, the sample was excited with the 532 nm line of a diode CW laser. The transmitted and emitted light were detected by a 0.3 m monochromator with a 1200 grooves/mm grating coupled to a CCDdetector. The samples were kept in a static flow cryostat at a temperature of 4.2 K during the measurements.
3. Results and discussion The absorption spectrum of the thin PIC film (Fig. 1) shows the characteristics of a J-aggregate with a narrow absorption band at 2.179 eV having a full-width at half-maximum (FWHM) of 41 meV. This is assigned to the exciton of the Jaggregate. Additionally absorption bands can be observed. The absorption spectrum is in agreement with absorption spectra of different PIC-salts (PIC-I, PIC-Cl, PIC-Br) in a polymer matrix [11– 13]. However, a shift to lower energies is visible due to the low temperature. (The low temperature PL spectrum of thin PIC-film is displayed in Fig. 1). Besides a sharp emission band at 2.169 eV, a broad emission band peaked at 1.979 eV is observed. The stokes shift is just 10 meV. We assign the sharp emission to the J-aggregate excition and the broad band emission to an emission from defect states [13]. Fig. 2a shows the low-temperature transmission spectra depending on the detuning between the exciton energy and the cavity photon mode. The exciton energy of the J-aggregate is defined as 0 meV. Far off resonance, at small angles (low energies), only one peak, corresponding to the cavity photon mode, can be observed. Tuning the photon mode energy to the energy of the exciton of the J-aggregate, an additional peak at higher energy appears and gains in integrated intensity. Between 291 and 301, the two peaks reach equal integrated intensities (see the arrow in Fig. 2a). Tuning to even higher angles, and hence higher energies of the cavity photon mode, a positive detuning is achieved. Here, the low-energy peak decreases in integrated intensity and finally disappears at around 341, whereas the high-energy
823
peak gains integrated intensity. The behavior described above is typical for the strong coupling regime in microcavities. At around 0 meV of detuning, the interaction between the cavity photon modes and the optical transition of the J-aggregate becomes large compared with the leakage channels. An emitted photon is reabsorbed before it escapes from the cavity. This leads to a mixing of the photon and exciton states. Two new eigenstates described as an admixture of the photon and exciton states are created. On resonance, at 0 meV detuning, both peaks have halfphoton and half-exciton character. A plot of the peak position depending on the cavity detuning (Fig. 3) shows a clear anticrossing of the two branches typical for the strong coupling regime. The closest proximity between the two branches (at 0 meV detuning), the so-called Rabi-splitting energy, is a measure of the interaction between the cavity photon mode and the optical transition. Here, the Rabi splitting energy is slightly bigger than 25 meV. In the weak coupling regime, the density of photon modes inside the cavity is different from the situation in the vacuum. Only a few photon modes are allowed due to the resonance conditions given by the restricted geometry. All other photon modes are suppressed. The cavity couples the optical transition of the material with the resonant photon modes. Therefore, photons have to be emitted into these allowed modes. Due to this coupling, a broad emission spectrum of the optically active material in the vacuum is reduced to the small spectral width of the allowed photon modes. In the strong coupling regime, however, the situation is different. Here, the simplest picture of the two coupled modes is a photon, that creates an exciton, that afterwards emits a photon. This process keeps on in a cyclic fashioned way [14]. Fig. 2b shows the low temperature PL spectra depending on the detuning between the exciton energy and the cavity photon mode. A scenario similar to the transmission spectra is observed. The peak position of the bands in the PL-spectra in the strong coupling-regime just resemble the dispersion curve for the transmission measurements in the strong coupling regime [10,15,16]. In Fig. 3, the peak position of the PL bands are plotted together
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Fig. 3. Peak position of the high-energy (circles) and low-energy (squares) bands for transmission (solid symbols) and PL (open symbols) spectra depending on the cavity detuning. The energy of the exciton of the J-aggregate is set as 0 meV. The dotted lines are a guide to the eyes. The two branches show a clear anticrossing behavior with a Rabi splitting of approximately 25 meV for the transmission measurement as well as for the PL measurement.
with the peak positions of the transmission bands. The peak positions of the two bands in transmission and PL are in good agreement. We assign this to a radiative emission from the two bands in the transmission measurements. Further measurements are under way to prove if the photoluminescence is thermalized, in that whether it follows the absorption spectra weighted by a Boltzmann population factor as it has been observed for
b—————————————————————————— Fig. 2. (a) Transmission spectra of the optical organic semiconductor microcavity at different angles between the main cavity axis and the measurement direction corresponding to different cavity detunings. The energy of the exciton of the Jaggregate is defined as 0 meV. Small angles correspond to large negative detunings, large angles to a large positive detuning. The arrow indicates the 0 meV detuning between 291 and 301. Inset: structure of the optical organic semiconductor microcavities used in this study. (b) PL spectra of the optical organic semiconductor microcavity at different angles between the main cavity axis and the measurement direction corresponding to different cavity detunings. The energy of the exciton of the Jaggregate is defined as 0 meV. Small angles correspond to large negative detunings, large angles to a large positive detuning. The arrow indicates the 0 meV detuning between 291 and 301.
semiconductor microcavities in the strong coupling regime [16]. 4. Conclusions High-quality optical organic semiconductor microcavities with a thin layer of homogeneously distributed J-aggregates of PIC as optically active material were prepared. The anticrossing behavior typical for the strong coupling regime in optical semiconductor microcavities has been observed in the transmission and photoluminescence measurements. The Rabi splitting in both cases is approximately 25 meV. Acknowledgements We thank A. Plekhanov and V.V. Shelkovnikov (Sibirian Branch of the Academy of Science, Novosibirsk, Russia) for providing the PIC material. The work was supported by the Deutsche Forschungsgemeinschaft (DA 287/5-1), Volkswagen Stiftung, Fond der Chemischen Industrie and the INTAS foundation (INTAS No. 97-10434).
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References [1] S. Haroche, D. Kleppner, Phys. Today 42 (1989) 24. [2] C. Weisbuch, M. Nishioka, A. Ishikawa, Y. Arakawa, Phys. Rev. Lett. 69 (1992) 3314. [3] D.G. Lidzey, D.D.C. Bradley, M.S. Skolnick, T. Virgili, S. Walker, D.M. Whittacker, Nature 395 (1998) 53. [4] D.G. Lidzey, D.D.C. Bradley, T. Virgili, A. Armitage, M.S. Skolnick, Phys. Rev. Lett. 82 (16) (1999) 3316. [5] D.G. Lidzey, T. Virgili, D.D.C. Bradley, M.S. Skolnick, S. Walker, D.M. Whittaker, Opt. Mater. 12 (1999) 243. [6] M.S. Skolnick, V.N. Astratov, D.M. Whittaker, A. Armitage, M. Eman-Ismael, R.M. Stevenson, J.J. Baumberg, J.S. Roberts, D.G. Lidzey, T. Virgili, D.D.C. Bradley, J. Lumin. 87–89 (2000) 25. [7] D.G. Lidzey, D.D.C. Bradley, A. Armitage, S. Walker, M.S. Skolnick, Science 288 (2000) 1620. . [8] H.v. Berlepsch, S. Moller, L. D.ahne, J. Phys. Chem. B 106 (2001) 5689.
[9] T.N. Gerasimova, N.A. Orlova, V.V. Shelkovnikov, Z.M. Ivanova, R.V. Morkov, A. Plekhanov, T.M. Polynskaya, V.V., Chem. Sustainable Dev. 8 (2000) 109. [10] R. Houdre, C. Weisbuch, R.P. Stanley, U. Oesterle, P. Pellandini, M. Ilegems, Phys. Rev. Lett. 73 (15) (1994) 2043. [11] D.A. Higgins, J. Kerimo, D.A. Vanden, Bout, P.F. Barbara, J. Am. Chem. Soc. 118 (1996) 4049. [12] T. Kobayashi, K. Misawa, J. Lumin. 72–74 (1997) 38. [13] M. Vacha, M. Furuki, T. Tani, J. Phys. Chem. B. 102 (1998) 1916. [14] V. Savona, L.C. Andreani, P. Schwendimann, A. Quattropani, Solid State Commun. 93 (1995) 733. [15] C. Weisbuch, R. Houdre, R.P. Stanley, in: H. Yokoyama, K. Ujihara (Eds.), Spontaneous Emission and Laser Oscillation in Microcavities, CRC, Boca Raton, 1995, p. 109. [16] R.P. Stanley, R. Houndre, C. Weisbuch, U. Oesterle, M. Ilegems, Phys. Rev. B 53 (16) (1996) 10 995.