journa l h om epa ge: www.elsev ier .com/ locate /synmet
uminescence features of nanocomposites of silicon-organicolymer/porous SiO2 and TiO2 films
. Ostapenkoa,∗, Yu. Ostapenkoa, O. Keritaa, D. Peckusb, V. Gulbinasb,. Eremenkoc, N. Smirnovac, N. Surovtsevac
Institute of Physics of NASU, pr. Nauki 46, Kiev 03028, UkraineCenter for Physical Science and Technology, Savanoriu 231, Vilnius, LithuaniaChujko Institute of Surface Chemistry of NASU, General Naumov street 17, Kiev 03164, Ukraine
r t i c l e i n f o
rticle history:eceived 22 November 2012eceived in revised form 4 October 2013ccepted 22 October 2013
a b s t r a c t
Photoluminescence properties of poly(di-n-hexylsilane) (PDHS) films as well as of PDHS adsorbed innanoporous silica and titania films, and dispersed in films of silica nanoparticles have been investigatedin a wide temperature range of 15–300 K. Photoluminescence spectra of all compounds were found to
vailable online 26 November 2013
eywords:rganic/inorganic nanocomposite filmsggregatesnhanced photoluminescence and lifetime
be dominated by the aggregate band. PDHS photoluminescence has been quenched by about 5 times innanoporous titania film in comparison with the silica film. Weak temperature dependences of PDHS pho-toluminescence intensities, lifetimes, band positions, and bandwidths have been observed in nanoporoussilica and titania films in comparison with neat PDHS film and PDHS dispersed in films of silica nanopar-ticles. It has been interpreted as a consequence of slow energy migration and weak photoluminescencequenching in nanoporous films.
. Introduction
�-Conjugated luminescent polymers are promising materialsor various photonic applications, such as active layers of light-mitting diodes [1–3], luminescent sensors and bioprobes [4–6].hotoluminescence (PL) quantum yield, which desirably shoulde close to 100%, is one of the major parameters determining theirpplication perspectives. Polymers usually have to be used in aolid state as thin films where macromolecules tend to form aggre-ates. It is known that aggregation of the organic polymers ofteneads to a partial or even complete quenching of their PL. Simulta-eously a decrease in the PL lifetimes is observed. This effect has
imited the scope of technological applications of the polymers.herefore substantial challenge is to discover and explore theechanisms and new functional properties of polymers when
ggregation plays a constructive, rather than destructive role.everal conceptions have been proposed to produce polymersith aggregation-enhanced emission (AEE): conformational pla-arization, J-aggregate formation, twisted intramolecular chargeransfer and restriction of the intramolecular rotation of individual
arts of macromolecules [7–10]. Theoretical and experimentalesearch of a number of authors [10,11] showed that the restric-ion of the intramolecular motion of macromolecules blocking the
∗ Corresponding author.E-mail address: [email protected] (N. Ostapenko).
nonradiative relaxation paths and activating the radiative decayis the most important mechanism of the AEE effect. As a result,polymers with AEE were synthesized by attaching propeller-like molecular structures of active hexaphenylsilanes ortetraphenylethenes to the polymer backbones [12,13].
We have recently investigated poly(di-n-hexylsilane) (PDHS)embedded into the SBA-15 nanoporous silica, obtained in a formof tablets pressed from porous powder [14]. It was shown thatthe PL quenching of the PDHS embedded in limited volumes ofSBA-15 nanopores is less effective. In the present work we ana-lyze a different way to obtain active polymers with AEE propertiesby incorporating macromolecules into nanopores of porous films.For this purpose we have developed a method of preparation oforganic/inorganic nanocomposite films, and investigated their PLspectra and PL lifetimes in a wide temperature range 15–300 K.As inorganic matrixes, we used nanoporous SiO2 and TiO2 filmswith given pore sizes and high surface area, as well as films ofdisperse SiO2 nanoparticles (nanosized SiO2). We have chosen �-conjugated silicon organic polymer PDHS as an organic component.This photoconductive and electroluminescent polymer has high PLquantum yield and high mobility of holes, which enables its appli-cation for emitting and transporting layers in electroluminescentdevices [15]. Our research results suggest that exciton diffusion and
related PL quenching are less efficient in PDHS in nanoporous SiO2and TiO2 films than in neat PDHS film or in PDHS dispersed betweenSiO2 nanoparticles. Weak exciton diffusion also causes weak tem-perature dependence of the PL intensity.
ig. 1. Electron microscope image of the SiO2 (a) and TiO2 (b) sol–gel films aftereat treatment at 623 K. The average pore diameter was of 10 nm.
. Experimental
Porous SiO2 and TiO2 films were obtained by sol–gel tem-late synthesis [16]. Precursors of tetraethoxy silane (TEOS) oretraisopropoxy titane (TIPT) were subjected to pre-hydrolysis inater–ethanol–1 M HCl solution at pH 2. Later, solution of template
gent, triblock copolymer poly(ethylene oxide)–poly(propylenexide)–poly(ethylene oxide)–EO20PO70EO20 (Pluronic P123,drich) in ethanol, was added, and reaction mixture was stirredigorously during 3 h. Porous films were prepared from the pre-ursor by “dip-coating” technique on glass or quartz substratesith the constant rate of 9 cm/min. Dry films were heat-treated
n a muffle furnace with a programmable heating regime (at aate of 1.5 ◦C/min up to 350 ◦C and 3 h kept at 350 ◦C). The surfacereas of the films were calculated from the adsorption–desorptionsotherms of hexane vapors, and were of 658 and 816 m2/g forhe SiO2 and TiO2 films respectively. The average pore diameteras calculated from the spectra of small-angle X-ray scattering
s being of about 10 nm. According to the electron-microscopiceasurements, the films had hexagonal pore structure (Fig. 1).To obtain PDHS/SiO2 or PDHS/TiO2 nanocomposite films, porous
iO2 or TiO2 films previously annealed at 350 ◦C were placed inDHS solutions in toluene (Mw = 53,600) with concentration of0−3 mol/l and were kept until reaching the adsorption equilibriumfter which the absorption spectra of the films did not change. Thenhe samples were washed by toluene to remove residual polymerrom the surface and dried to remove the solvent. Localization ofhe polymer in the pores and the degree of the pore filling was eval-ated from the absorption spectra of nanocomposites [17], taking
nto account that the porous films of silicon and titanium dioxidesre transparent in the polymer absorption region. The absorptionands of nanocomposites remained quite intense, even after wash-
ng of films in toluene up to 150 min. It indicates that the bonding
Metals 187 (2014) 86– 90 87
strength of the polymer chains with the matrix was strong enoughto prevent desorption, and allows as to suggest that polymer chainswere dominantly located in the pores. A simple dispersion interac-tion may be sufficient to keep the polymer adsorption on the surfaceof the pores. This is also evidenced by the fact that the polymer film,which was deposited by spin casting on the outer surface of theporous film, was easily washed with toluene within 15 min. How-ever, we cannot exclude a possibility that fractions of long polymerchains remained outside the pores.
To get another kind of the samples, we will call them asPDHS/nanosized SiO2 composites, nanosized SiO2 particles of about2 nm in diameter were dispersed in the 10−3 mol/l polymer solu-tion in toluene and slowly stirred in dark for several hours. Thenthis solution was deposited on a glass substrate by spin coating.
Neat polymer films were also prepared for comparison by apply-ing PDHS solution in toluene with concentration of 4.3 × 10−2 mol/lon surfaces of porous films or on glass substrates and drying with-out further washing.
PL spectra and decay kinetics of the samples were measuredusing Edinburgh Instruments time-correlated single photon count-ing (TCSPC) fluorescence spectrometer F900. The sample excitationwas performed by light emitted diode with 283 nm peak wave-length and about 15 nm bandwidth. The pulse duration was ofabout 750 ps and the repetition rate was 20 kHz. A liquid heliumcold finger cryostat (Janis CCS-100/204) was used for temper-ature dependent measurements in 15–300 K range in a slowcooling regime. PL relaxation lifetimes measured by TCSPC weredetermined by approximation of emission kinetics with multiex-ponential functions together with deconvolution of the apparatusfunction. Deconvolution procedure allowed us to determine shorterrelaxation times than the excitation pulse duration.
3. Result and discussion
3.1. Photoluminescence spectra of PDHS/inorganicnanocomposite films
Fig. 2a shows absorption and PL spectra of PDHS/SiO2 andPDHS/TiO2 nanocomposite films at room temperature. Absorptionspectra show two clearly separated bands with slightly differentpeak positions for SiO2 and TiO2 matrixes. Based on the analysisof the PDHS polymorphism [18,19] the absorption band at about310 nm should be attributed to the gauche polymer chain confor-mation, while the long wavelength band at about 360 nm, to theaggregate states. The strong aggregate band indicates that severalpolymer chains are situated inside single pore and a large frac-tion of them form aggregates. Despite the sample excitation to thegauche conformer absorption band, the PL spectra are dominatedby the aggregate band at about 380 nm, while gauche conformerband at about 340 nm has only low intensity. It indicates that exci-tation energy is efficiently transferred from gauche conformers toaggregate states.
At 15 K temperature (Fig. 2b) the aggregate band shifts to theshort wavelength side, while the gauche PL band is replaced by thenew band at about 355 nm, which shall be attributed to the transpolymer chain conformation formed at low temperature [18,19]. Itshould be also noted, that the relative intensities of the two bandsdepend on the polymer concentration in the solution used for thefilm preparation; intensity of the short wavelength band grows upwith decreasing the polymer concentration down to C = 10−4 mol/l.It indicates that occupation of the film pores decreases at low solu-
tion concentration, and less aggregate states are being formed. Thelong wavelength band in the PL spectrum of PDHS/SiO2 is about2.5 times as intense as that in the spectrum of PDHS/TiO2. Fig. 2cshows PL spectra at 15 K of the PDHS/nanosized SiO2 and of neat
88 N. Ostapenko et al. / Synthetic Metals 187 (2014) 86– 90
Fig. 2. (a) absorption and PL spectra of PDHS/TiO2 and PDHS/SiO2 films at roomtemperature, (b) PL spectra of PDHS/TiO2 and PDHS/SiO2 films at 15 K temperature,(fi
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DHS polymer films, as well as that of PDHS/SBA-15 (curve 4)anocomposite powders with pore diameter of 10 nm discussed inef. [18].
Comparison of the PL spectra of composite films with the ear-ier reported spectra of the PDHS/SBA-15 powders gives us morenformation about the conformation of PDHS polymer chains inimited volumes of silicon and titanium dioxide pores in films.t is well known that conformation of the PDHS polymer chainsocalized in the SBA-15 nanoporous silica, and consequently theirpectra are significantly different from the conformation and spec-ra of the neat polymer films. As Fig. 2c shows the PL spectrumf the neat polymer film consists of a single band with a maxi-um at 373 nm, while PDHS/SBA-15 composite has three spatially
ndependent centers of the polymer, which correspond to isolatedolymer chains in the gauche- and trans-conformations and to theirggregates [14,20]. The gauche-, trans- and aggregate centers haveL bands at 337, 355 and 369 nm (T = 15 K) respectively. Fig. 2chows that the PL spectrum of the PDHS/nanosized SiO2 compositeas almost identical PL bands to those of PDHS/SBA-15 compos-
te. This fact allows us to attribute the long wavelength PL band ofDHS/nanosized SiO2 composite to the PDHS aggregates [21]. TheL spectra of PDHS/SiO2 and PDHS/TiO2 nanocomposite films showhe same bands and hence the same conformations of the poly-
er chains, however, intensities of the bands are different (Fig. 2).hus, PDHS polymer chains in limited volumes of SiO2 and TiO2anopores, basically, form aggregates and the bands correspond-
ng to the transitions in the isolated polymer chains in gauche- andrans-conformations are very weak. Less efficient aggregate for-
ation in SBA-15 silica matrix is most probably related to lowerelative occupation of the matrix pores by polymer chains. Dif-erent morphologies of the porous materials apparently are also
mportant for the aggregate formation. SBA-15 synthesized usinghe same template – Pluronic P123, but without applying to theubstrate has higher degree of order than porous films, because
Fig. 3. Temperature dependence of the integral aggregate PL band intensity ofPDHS/SiO2, PDHS/TiO2, PDHS/nanosized SiO2, and of the neat PDHS films.
influence of the substrate leads to the structure destruction dur-ing drying and heat treatment of the films [16,22]. The fact thatthe pores of the film are closed on the one side by the substratecan create additional steric hindrance for penetration of long poly-mer chains into the pores, with depths of about 50 nm, comparablewith the polymer chain lengths. In this case, the ends of the poly-mer chains leaving from the neighboring pores can form aggregatesdue to van der Waals interactions between them.
Relative PL intensities of the PDHS/SiO2 and PDHS/TiO2 com-posites deserve additional consideration. PDHS/TiO2 film hadapproximately twice as large optical density at excitation wave-length as PDHS/SiO2 film, but its PL intensity was about 2.5 timeslower, indicating about 5 times lower PL yield. TiO2 is a strongelectron acceptor, and is expected to strongly quench polymer PLby electron transfer from photo-excited polymer macromoleculesto the electron-acceptor centers, namely coordinative unsaturatedtitanium ions and oxygen vacancies [23,24]. Therefore relativelyweak PL quenching remains not completely clear. One of the possi-ble explanations is that the polymer chains touch walls of the poresonly by their long hexyl substitutions, keeping relatively large dis-tances between polymer backbone and TiO2, and thus preventingfast electron transfer. Another possibility is that only the ends ofthe polymer chains sticking out of the pores are responsible for thePDHS/TiO2 PL. The later explanation is less likely, because PL spec-tra of PDHS/TiO2 and PDHS/SiO2 composites are very similar, whilepolymer chains inside and outside pores are expected to have dif-ferent spectra. Therefore PL spectra of the two composites are alsoexpected to be different if only polymers chain segments locatedoutside pores are responsible for the PDHS/TiO2 film PL, while PL ofPDHS/SiO2 film originates both from segments inside and outsidepores.
Fig. 3 shows temperature dependences of the integral intensitiesof the aggregate PL bands of the investigated samples in the temper-ature range of 15–296 K. The temperature dependences obtainedfor the PDHS/SiO2 and PDHS/TiO2 films are significantly differentfrom those obtained for the PDHS/nanosized SiO2 composite andfor the neat polymer film: intensity of the aggregate band of thePDHS/SiO2 and PDHS/TiO2 films weakly depend on temperature,even slightly increases above 200 K, while PL intensity drops down
twice at room temperature in the case of PDHS/nanosized SiO2composite and of neat PDHS film. Similar temperature independentPL relaxation has been determined for PDHS/SBA-15 composite
N. Ostapenko et al. / Synthetic Metals 187 (2014) 86– 90 89
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ig. 4. Temperature dependence of the aggregate PL band positions (a) and half-idths (b) of different PDHS samples.
owder [25] and attributed to the weak exciton diffusion. Theame conclusion is evidently also valid for the composite films.olymer chains located in different film pores are separated fromach other, preventing exciton transfer between them. Even if PLf the composite film partly originates from the polymer chainsticking out of the pores, the density of such chains is apparentlyoo low to create sufficiently dense network for efficient exci-on migration. In contrast, polymer chains in neat PDHS film andn PDHS/nanosized SiO2 composite are closely packed, enablingfficient and temperature dependent exciton migration and con-equently quenching by some impurities, defects, or other kindf quenching centers present in the polymer. Fig. 4 presents theemperature dependences of the aggregate PL band peak positionsnd of the band widths. Both these dependences are signifi-antly weaker for the nanocomposite films than for the neatDHS film. It supports the conclusion that the exciton diffusions much less efficient in the nanocomposite films; excitons local-ze on the low energy sites in the neat film causing the relativelytrong bathochromic PL band shift and the band broadening withemperature.
.2. Photoluminescence relaxation dynamics of PDHS/inorganicanocomposite films
Fig. 5 shows the PL relaxation traces measured at 30 K andt room temperature. The PL kinetics were approximated byi-exponential relaxation function with deconvolution of the appa-atus function. Deconvolution procedure allowed us to determinehorter relaxation times than the excitation pulse duration. Inddition to the main relaxation component with subnanosecondifetime, all kinetics have a weak component with several ns life-
ime. The weak component is probably caused by some impuritiesresent in nanocomposites. Its contribution is less than 1% there-ore we did not analyze it in detail. The PL decay kinetics of thenvestigated PDHS samples are in good agreement with the above
Fig. 5. PL decay kinetics of PDHS/TiO2 (a), PDHS/SiO2 (b) and of PDHS/nanosizedSiO2 films (c) measured at the maxima of the aggregate PL bands at 30 K and 296 Ktemperatures. The gray line in (c) shows the impulse response function.
described temperature dependences of the PL intensity. The domi-nating PL lifetimes of both nanocomposite films are slightly longerat 296 K than at 30 K in agreement with the temperature depend-ence of the PL intensity. A similar temperature independent PLdecay has been observed for PDHS in SBA-15 matrix [25]. In con-trast, PL lifetimes of the PDHS/nanosized SiO2 composite decreaseabout 1.3 times by their heating from 30 K to room temperature,similarly as was reported for the neat PDHS films [26]. Attributingthe PL decay to the exciton quenching via temperature activateddiffusion, we conclude that exciton diffusion in PDHS embeddedin porous films is relatively slow, like in SBA-15 matrix, while inPDHS/nanosized SiO2 film the diffusion is much more effective,like in neat PDHS films. It should be also noted, that the PL life-times of nanocomposite films are still about 1,5–2 times shorterthan in SBA-15 silica [25]. It suggests that the polymer chains innanoporous films are less ordered and/or isolated from quenchingcenters than in SBA-15 matrix.
Comparing PL decay kinetics in porous SiO2 and TiO2 films weobserve even less significant difference between PL lifetimes thanbetween their intensities. This disagreement may be attributed tothe very fast quenching component of PDHS/TiO2 film PL, unre-solved by our measurements, however it may be also causedto some experimental problems like film inhomogeneity, samplepositioning, degradation etc., causing inaccuracy of the PL intensitymeasurements.
4. Conclusions
Photoluminescence properties of nanocomposite PDHS/SiO2and PDHS/TiO2 films, as well as of the PDHS/nanosized SiO2 com-posite and of the neat PDHS film have been investigated in a
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emperature range of 15–300 K. PDHS PL yield is about 5 timesower and its lifetime about 1.4 times shorter in porous TiO2 filmhan in porous SiO2 film. We suggest that the relatively weak PLuenching TiO2 film is caused by the long hexyl side groups, whichrevent close contacts between polymer backbone and pore surfacereventing electron transfer, or, less probably, by PL of the polymeregments sticking out of the porous film. PL of the all investigatedomposites is dominated by the aggregate band. Weak temperatureependences of the PDHS PL intensities, lifetimes, band positions,nd bandwidths of nanocomposite films in comparison with thosef the neat PDHS film indicate that the exciton diffusion is much lessfficient in composite films than in the neat film, and consequentlyL quenching by some quenching centers present in polymer isess efficient. Thus, nanocomposite films is a promising technolo-ically convenient approach of preparation of polymer films withmproved PL properties.
cknowledgements
The authors are grateful to Prof. A. Watanabe for polymer syn-hesis. This work was partially financed by Ukrainian Ministry ofducation and Science and by the Research Council of Lithuaniahrough the Lithuanian-Ukrainian collaboration project.
[2] D.Y. Kim, H.N. Cho, C.Y. Kim, Blue light emitting polymers, Prog. Polym. Sci. 25(2000) 1089–1139.
[3] M. Shimize, T. Hijama, Organic fluorophores exhibiting highly efficient photo-luminescence in the solid state, Chem. Asian J. 5 (2010) 1516–1531.
[4] M. Wang, G.X. Zhaug, D.Q. Zhaug, D.B. Zhu, B.Z. Tang, Fluorescentbio/chemosensors based on silole and tetraphenylethene luminogens withaggregation-induced emission feature, J. Mater. Chem. 20 (2010) 1858–1867.
[5] S.W. Tomas, G.D. Joly, T.M. Swage, Chemical sensors based on amplifying fluo-rescent conjugate polymers, Chem. Rev. 107 (2007) 1336–1386.
[6] B. Adhikari, S. Majumdar, Polymers in sensors application, Prog. Polym. Sci. 29(2004) 699–766.
[7] J. Lin, J.W.V. Lam, B.Z. Tang, Aggregation-induced emission of silole molecules
and polymers: fundamental and applications, J. Inorg. Organomet. Polym. 19(2009) 249–285.
[8] Y. Ren, J.W.V. Lam, Y.A. Dong, B.Z. Tang, K.S. Wong, Enhanced emission effi-ciency and excited state lifetime due to restricted intramolecular motion insilole aggregates, J. Phys. Chem. B 109 (2005) 1135–1140.
[
Metals 187 (2014) 86– 90
[9] B.R. Gao, H.Y. Wang, Y.W. Hao, L.M. Fu, H.H. Fang, Time-resolved fluores-cence study of aggregation-induced emission enhancement by restriction ofintramolecular charge transfer state, J. Phys. Chem. B 114 (2010) 128–134.
10] Y.H. Hong, J.W.V. Lam, B.Z. Tang, fluorescent chemosensor for detection andquantitation of carbon dioxide gas, Chem. Commun. (2009) 4332–4353.
11] I. Chen, C.C.W. Law, J.W.V. Law, V. Dong, et al., Synthesis, light emission,nanoaggregation, and restriction intramolecular rotation of 1,1-substituted2,3,4,5-tetraphenylsiloles, Chem. Mater. 15 (2003) 1535–1546.
13] W.Z. Yuan, H. Zhao, X.Y. Shen, F. Mahtab, J.W.Y. Lam, J.Z. Sun, B.Z. Tang,Disubstituted polyacetylenes containing photopolymerizable vinyl groups andpolar ester functionality: polymer synthesis, aggregation-enhanced emission,and fluorescent pattern formation, Macromolecules 42 (2009) 9400–9411.
14] A. Dementjev, V. Gulbinas, L. Valkunas, N. Ostapenko, S. Suto, A. Watanabe,Coexistence of different conformer forms in nanosize poly(di-n-hexylsilane), JPhys. Chem. 111 (2007) 4717–4721.
15] A.H. Suzuki, H. Meyer, S. Hohino, et al., Electroluminescence from multilayerorganic light-emitting diodes using poly(methylphenylsilane) as hole trans-porting material, J. Appl. Phys. 78 (1995) 2684–2691.
16] G.V. Krylova, Yu.I. Gnatyuk, N.P. Smirnova, A.M. Eremenko, V.M. Gunko, Agnanoparticles deposited onto silica, titania, and zirconia mesoporous filmssynthesized by sol–gel template method, J. Sol–Gel Sci. Technol. 50 (2009)216–228.
17] N.I. Ostapenko, N.V. Kozlova, E.K. Frolova, et al., Spectral properties of silicon-organic polymer SiO2 porous film nanocomposites films, J. Appl. Spectr. 98(2011) 75–80.
zation and orientation in ultrathin films: a spectroscopic investigation, J. Polym.Sci. B 34 (1996) 2335–2349.
20] N. Ostapenko, N. Kozlova, S. Suto, A. Watanabe, Spectroscopy of nanosized com-posites consisting of silicon-organic polymers in nanoporous silicas, Fiz. Nizk.Temp. 32 (2006) 1363–1371.
21] A.I. Kuznetsov, O. Kameneva, N. Bityurin, et al., Laser-induced photopattern-ing of organic–inorganic TiO2-based hybrid materials with tunable interfacialelectron transfer, Phys. Chem. Chem. Phys. 11 (2009) 1248–1257.
22] A.M. Gunko, V.V. Turov, A.V. Turov, V.I. Zarko, V.I. Gerda, et al., Behavior of purewater and water mixture with benzene or chloroform adsorbed onto orderedmesoporous silicas, Cent. Eur. J. Chem. 5 (2007) 420–454.
23] G. Staruch, N. Smirnova, A. Eremenko, et al., Laser-induced electron transferprocesses in complex pyrene-b-cyclodextrin in titanosilicate systems, Theor.Exp. Chem. 37 (2001) 100–104.
24] A. Kathiravan, V. Anbazhagan, M. Asha Jhonsi, R. Renganathan, A Study on thefluorescence quenching of eosin by certain organic dyes, Z. Phys. Chem. 222(2008) 1013–1021.
25] K. Kazlauskas, A. Dementjev, V. Gulbinas, L. Valkunas, P. Vitt, A. Zukauskas, N.
Ostapenko, S. Suto, Temperature independent exciton relaxation in poly(di-n-hexylsilane) confined in nanoporous silica, Chem. Phys. Lett. 465 (2008)261–264.
26] M. Shimizu, S. Suto, T. Goto, et al., Temperature dependence of exciton dynamicsin poly (di-n-hexylsilane), Phys. Rev. B 63 (2001) 073403–073406.
