Influence of Photonic Crystal on Fluorescence Resonance Energy

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Influence of Photonic Crystal on Fluorescence Resonance Energy Transfer Efficiency between Laser Dyes Sunita Kedia, and Sucharita Sinha J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp512954p • Publication Date (Web): 27 Mar 2015 Downloaded from http://pubs.acs.org on March 30, 2015

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The Journal of Physical Chemistry

Influence of Photonic Crystal on Fluorescence Resonance Energy Transfer Efficiency Between Laser Dyes *

Sunita Kedia and Sucharita Sinha

Laser and Plasma Technology Division, Bhabha Atomic Research Centre, Mumbai 400 085, India

*

Corresponding author: Sunita Kedia Laser and Plasma Technology Division Bhabha Atomic Research Centre Mumbai, India 400 085 E-mail: [email protected] Tel no: + 91-22-25595352

1 ACS Paragon Plus Environment


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Abstract: Spontaneous emission by an excited molecule strongly depends upon the available density of states into which the molecule can decay. In a photonic crystal, the allowed local density of states depletes within the stop band and enhances at the band edge of the crystal. As a result, an emitter implanted in a photonic crystal is forced to redistribute its fluorescence energy within its emission spectral range and its spontaneous emission spectrum thus gets modified. Here, we studied the influence of change in local density of states on energy transfer efficiency between a donor-acceptor pair embedded in a colloidal photonic crystal. Rhodamine-B and Rhodamine-800 dyes were chosen as energy donor and energy acceptor, respectively. We observed, an angle dependent quenching in the emission intensity of donor accompanied by enhancement in acceptor emission when both dyes were in photonic crystal. This occurred owing to depletion in the allowed local density of states available to the donor. Reduction in fluorescence lifetime of the donor in presence of acceptor confirmed fluorescence resonance energy transfer between the chromophores. In spite of marginal overlapping between emission band of donor and absorption band of acceptor, the energy transfer efficiency between the dyes was ~80% in photonic crystal environment. This enhancement resulted from forced proximity and hence, reduced intermolecular distance between donor and acceptor on being physically restricted within nano-voids of the photonic crystal.

Keywords: Photonic Band Gap, Energy Transfer, Donor-Acceptor pair, Rhodamine-B, Rhodamine-800


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1. Introduction:

Three-dimensional (3-D) photonic crystals (PhC) have been investigated widely because they provide a handy route to control and alter the propagation of electromagnetic waves. PhC are artificial structures with periodic distribution of two or more dielectrics such that the periodicity matches with optical wavelength. When electromagnetic waves interact with lattice planes of the PhC, specific wavelengths are prohibited from propagating through the crystal in certain directions and as a result, high transmission losses are observed over this spectral range. This happens because of restricted availability of local density of state (LDOS) for photons in these specific directions. This restricted wavelength range is referred to as photonic stop band of the PhC. For low refractive index contrast between constituent materials, the PhC possesses an angle dependent stop band. Hence, LDOS is an angle dependent parameter in such crystals. Since spontaneous emission of active materials is proportional to the available LDOS,1 such PhC have been used effectively to modify the spontaneous emission of a variety of emitters implanted in it.2-5 PhC with angle dependent stop band have also been used as sensors,6 antennas,7 and photovoltaic devices8. However, PhC with high refractive index contrast disallows a particular range of wavelength to propagate through it in all directions and for all polarizations. In this case, the crystal exhibits complete band gap and available density of state is depleted for this specific wavelength range for all directions of propagation. Such PhC have been exploited to demonstrate low threshold lasing 9 and wave guiding10. There are mainly two approaches for fabrication of PhC, lithography

11

and self-

assembly.12 Among these, self-assembly is found to be a simple yet, stable, reproducible and cost effective method for synthesis of 3-D PhC. In self-assembly technique, organic or



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inorganic mono-dispersed micro-colloidal particles are allowed to grow on substrates such as glass or silicon wafer under ambient conditions. Under suitable environment, the microparticles or globules get arranged into face-centered cubic (FCC) lattice structure with approximately 26 % of air voids in its volume.

Foreign species can subsequently be

infiltrated into these voids for desired applications.13-14 Infrared radiation in the region of 700 nm to 1300 nm easily transmit through tissues and hence find wide application in phototherapy and non-invasive optical detection in clinical medicine.15 However, a significant disadvantage associated with most IR emitting dyes is that they have poor absorption at 532 nm, second harmonic radiation of Nd:YAG laser, that is commonly used for their optical pumping. Rhodamine-800 (Rh-800) dye, a member of the Xanthene derivatives characterized by excellent photostability and fluorescent yield is one such IR dye that emits efficiently in the near IR range. One technique adopted to overcome its poor absorption at 532 nm is to use a combination of dyes as a donor-acceptor (D-A) pair. In this case, the donor dye efficiently absorbs at 532 nm and transfers this energy to the IR dye molecule. Rhodamine-B (Rh-B) dye having strong absorption at 532 nm often serves as an efficient donor dye. Hence, Rh-B and Rh-800 forms a potential D-A combination enabling efficient IR emission when excited with a 532 nm pump source. Energy transfer between donor and acceptor occurs via both radiative and non-radiative channels. Among non-radiative energy transfer pathways fluorescence resonance energy transfer (FRET) is an energy transfer mechanism by which an excited donor transfers energy to an acceptor in ground state through long-range dipole-dipole interactions. The rate of energy transfer via this process depends on various factors, such as the extent of spectral overlap between emission band of donor and absorption band of acceptor, relative orientation of the transition dipoles and the distance between the donor and the acceptor species.16 The efficiency of energy transfer has a dependence of (Ro/R) 6 where Ro is the Forster radius and


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R is the inter-molecular distance.17 FRET is a dominant energy transfer mechanism between emitters when separated by 1-10 nanometer. FRET mechanism has tremendous application in chemistry, biology, and physics because of its non-interference characteristics, sensitivity, real time observation capability, fast response, and specificity. FRET process has been used for microscopic imaging and data analysis.18 Gambin et al used single-molecule FRET with multicolour measurements to probe complex distributions, dynamics, pathways, and landscapes in protein folding and binding reactions.19 Ma et al demonstrated FRET based ratiometric sensor for Hg2+ in pure water.20 Chatterjee et al used FRET mechanism as spectroscopic ruler.21 Recently, Ray et al discussed about the light focusing properties of plasmonic nanoparticles which are useful in the development of long range one-dimensional to three-dimensional FRET based optical rulers that can monitor biological and chemical processes.22 Bujdak et al. observed FRET between Rhodamine 123, rhodamine 610 and oxazine 4 fluorophores embedded in silicate laponite film.26 FRET has also been observed between pyrromethene 567 and rhodamine 610 in ethanol modified poly(methyl methacrylate) matrix by Li et al. 27 and between rhodamine 6G and oxazine 4 dyes in saponite dispersions medium by Czmerova et al.28 FRET mechanism between various laser dyes embedded in a PhC, have been reported by various groups.29-32 In most of these reports, emission spectrum of donor overlapped the absorption band of acceptor. In the study being reported, a PhC with a tunable stop band has been employed to investigate energy transfer from an energy donor (Rh-B) to an energy acceptor (Rh-800). While the donor dye molecules doped in polystyrene colloidal spheres were used to synthesize the PhC, an ethanolic solution of acceptor molecules was infiltrated in the PhC voids. Energy transfer efficiencies between these two dyes in solution and in PhC were compared. Owing to poor spectral overlap between emission spectrum of Rh-B and



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absorption band of Rh-800, clear evidence of energy transfer between this D-A pair in solution could be observed only when concentration of acceptor was raised to 100 times higher than that of donor in the dye mixture solution. However, when the D-A pair was placed within PhC such that, the photonic stop band overlapped the donor emission, efficient energy transfer from donor to acceptor occurred at much lower acceptor concentrations (~ 10 times donor concentration).

2. Experiment: 3D PhC were fabricated using Rh-B dye doped polystyrene colloidal spheres with mean sphere diameter of 302 nm by inward growing self-assembly technique.12 In this process, an optimized volume of a colloidal solution of dyed polystyrene microspheres was spread on glass substrates and allowed to dry in ambient. Within 3-5 hr, the polymer globules self arranged in FCC lattice structure with tetrahedral and octahedral interconnected voids of sizes around 33 nm and 62 nm, respectively.33 Scanning electron microscope (SEM) images were recorded to know the structural quality of the PhC. Stop band characterization was done by measuring reflectance and transmittance of the PhC using a spectrophotometer. To estimate concentration of Rh-B dye in polymer beads, the PhC was dipped in known volume of ethanol for one day, thereby ensuring all of the Rh-B dye doped in the PS spheres dissolved in ethanol leaving behind bare PhC on the substrate. In this manner, concentration of Rh-B in PhC was estimated to be 0.005 mM. Energy transfer between the D-A pair was studied under two conditions: in a dye mixture solution and with dyes embedded in the PhC matrix. In the former case, Rh-B and Rh-800 fluorophores were dissolved in ethanol and emissions were collected for different concentrations of acceptor with donor concentration held constant at 0.005 mM. For investigating energy transfer mechanism in PhC


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environment, Rh-B doped PhC was dipped in ethanolic solution of acceptor in a cuvette such that the acceptor molecules with ethanol infiltrated the crystal voids. The samples were excited at 532 nm with nanosecond pulsed radiation from a frequency doubled Nd:YAG laser and fluorescence was characterized using an optical fibre based spectrometer (Avantes, AvaSpec-2048XL). Fluorescence decay lifetime measurements were carried out using a time-correlated single-photon-counting (TCSPC) spectrometer (1BH, UK). The excitation source consists of a pulsed light emitting diode at 490 nm delivering 1.3 ns pulses at 1 MHz repetition rate. Samples were excited at 490 nm and the decay signals at 590 nm were recorded using a photo multiplier tube. The observed fluorescence decay was analyzed by a convolution procedure using a proper instrument response function. For better time resolution, ultrafast decay lifetime of the PhC in absence and in presence of acceptor was performed using a femtosecond fluorescence upconversion spectrometer (FOG 100, CDP Inc. Russia). The samples were excited at 400 nm with second harmonic of Ti:Sapphire laser having pulse duration of 50 fs and at repetition rate 88 MHz. The instrument response function measured independently shows Gaussian intensity profile with temporal width of 220 fs. Emission decays of the samples were recorded by keeping the sample in rotating cell to avoid photobleaching of the embedded dyes. The fluorescence decay was analyzed as a sum of exponentials as 34

= ∑ exp −/

(1)

where I(t) is the time-dependent fluorescence intensity. Bi and τi are the pre-exponential factor and fluorescence lifetime for the ith component of fluorescence decay, respectively.



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The quality of fit and consequently the mono- or bi- exponential nature of the decays were assessed by χ2 values and the distribution of the weighted residuals among the data channels.

3. Results and Discussion:

3.1 Photonic crystal characterization:

(a)

(b)

Fig. 1: SEM image of Rh-B doped PhC (a) hexagonal arrangement of micro-spheres on top surface of the crystal represent plane of face centered cubic lattice structure, and (b) cross-sectional view shows extent of closed packed layers in the crystal

The PhC contains finite number of close packed layers of hexagonally arranged RhB dye doped polystyrene spheres. Fig. 1a and 1b are the scanning electron microscope (SEM) images of the top surface (parallel to the substrate) and cross-section of the PhC, respectively. Well-ordered polymer beads in hexagonal geometry in Fig. 1a indicate the plane of FCC lattice structure. Sectional view of the PhC confirms uniform thickness with large extent of ordered layers in the structure.


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Fig 2: Reflection (solid line) at 10o transmission (dashed line) at normal incidence spectra of PhC, inset is reflection spectra of PhC at different angles Characterization of photonic stop band and emission studies of embedded dyes were performed from the plane along ΓL direction of the crystal. To identify photonic stop band, reflection and transmission spectrum of PhC are shown with solid and dashed lines in Fig. 2, respectively. The reflection spectrum shows peak reflectance of ~71% at 605 nm for near normal incidence (10o). This is associated with a corresponding trough in transmission spectrum. In the figure, peak reflectance appears blue shifted by 4nm in comparison to transmission dip, as transmission measurement was done at normal incidence while reflection was recorded at near normal (10o) incidence. The full width at half maxima (∆λ) of the reflection spectrum is 42 nm. About 30 numbers of ordered layers in the crystal was estimated from the Fabry-Perot oscillation observed on either side of reflection spectrum.35 These oscillations are indication of uniform thickness of the crystal with identical orientation of the crystal domains and good ordering of each layer in the depth. Angle resolved reflection spectra of the PhC are shown in the inset of Fig. 2. The reflection spectrum blue shifted at 9 ACS Paragon Plus Environment


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larger angles representing the pseudo band gap nature of the crystal. However, ∆λ remained same (~ 42 nm) for all angles once again signifying well-ordered layers in the crystal with fewer defects.

3.2 Spectral properties of donor-acceptor pair:

Fig. 3: (a) Normalized absorption spectra of Rh-B (solid line) and Rh-800 (dotted line) dyes in ethanol, and (b) Normalized emission spectra of Rh-B in solution (thick line), in PhC (thin line) at 532 nm excitation and absorption spectrum of Rh-800 (dotted line) Fig. 3 depicts absorption and emission spectra of chosen donor and acceptor dyes. Solid line in Fig 3a is the normalised absorption spectrum of Rh-B dissolved in ethanol showing maximum absorbance at 542 nm. The peak absorption of acceptor is at 681 nm, shown with dotted line in Fig. 3a. While the donor has considerable absorption at 532 nm the acceptor dye Rh-800 has negligible absorption at this wavelength. Thick line in Fig. 3b is the normalized emission spectrum of Rh-B in ethanolic solution for excitation at 532 nm. There is a marginal spectral overlap between emission spectrum of donor and absorption spectrum of acceptor (dotted line). Modified environment and unavoidable defects in artificial PhC shifted the Rh-B emission peak from 563 nm to 586 nm and broadened it by 34%, as depicted


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by thin line in Fig. 3b. This resulted in an increased spectral overlap between emission of RhB and absorption spectrum of Rh-800 within the PhC. Hence, in a PhC environment, rate of energy transfer from donor Rh-B to acceptor Rh-800 is expected to improve on account of this increased spectral overlap.

Fig. 4 : (a) Emission spectra of D-A in dye mixture solution at 532 nm excitation, with fixed donor concentration at 0.005 mM and acceptor concentrations 0.005 mM (thin line), 0.05 mM (dotted line), 0.5 mM (dashed line), and acceptor (thick line) alone at concentration 0.5 mM, and (b) ratios of integrated emission of acceptor to integrated emission of donor for different concentrations of acceptor

In our study, extent of energy transfer from D to A was first investigated in a homogenous dye mixture solution. Fig. 4a shows the emission spectra of the mixture when concentration of Rh-B was fixed at 0.005 mM and concentration of Rh-800 was varied stepwise from 0.005 mM, to 0.5 mM. For 0.005 mM concentration of acceptor in the mixture, the emission from Rh-800 was negligible in comparison to RhB, as shown with thin line in Fig. 4a. However, acceptor emission intensity increased gradually when its concentration was increased to 0.05 mM, and then to 0.5 mM, as shown by dotted and dashed lines in Fig. 4a. Significant quenching in donor emission intensity along with noticeable enhancement in acceptor emission intensity occurred for 0.5 mM concentration of acceptor. This exhibits



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occurrence of energy transfer in the D-A pair. To confirm role of dye Rh-B in effectively transferring pump energy to Rh-800 dye molecules, an ethanolic solution of only Rh-800 at a concentration of 0.5 mM was excited at 532 nm. No detectable emission was observed from this solution containing acceptor alone, as shown with thick line in Fig. 4a. This establishes the fact that donor Rh-B act as a conduit transferring pump energy to acceptor Rh-800 enabling fluorescence from Rh-800 when pump source is at 532 nm. Integrated emission ratios of acceptor to donor for varying concentrations of Rh-800 in mixture solution are shown in Fig. 4b.The ratio increased with acceptor concentration indicating quenching of donor emission intensity in presence of acceptor. With further increase in acceptor concentration, this ratio showed a flattening trend indicating all donor molecules had been exhausted in this regime.

Fig. 5: Emission spectra of Rh-B doped PhC dipped in acceptor solution of concentration 0.05 mM (a) at 10o (solid line), reflection spectra of PhC at 10o in air (thin line) and in ethanol (dashed line), and (b) at different angles (solid lines) and at 10o (dashed lines)

To explore energy transfer between chosen dyes in PhC environment, the dyed PhC was dipped in Rh-800 dye solution in a cuvette and pumped at normal incidence. Thick line in Fig. 5a depicts the emission spectrum of the dyes implanted PhC recorded at 10o when 12 ACS Paragon Plus Environment

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concentrations of donor and acceptor were 0.005 mM and 0.05 mM, respectively. The peaks around 582 nm and 720 nm correspond to emission from D and A, respectively. After immersion, the acceptor dye molecules along with ethanol seeped into the air-voids of the PhC and as a result the effective refractive index of crystal increased by 5.5 %. Because of higher index ethanol in the voids, the photonic stop band red-shifted by ~ 50 nm. Thin and dashed lines in Fig. 5a are the reflection spectra of PhC in air and in ethanol recorded at 10o, respectively. In this situation, the stop band moved beyond the emission range of donor and hence could not strongly modify the energy transfer process between Rh-B to Rh-800. For the stop band of PhC to positively affect and enhance transfer of energy from donor to acceptor the stop band should necessarily overlap the donor emission. For this, the emissions were recorded at larger angles of incidence such as, angles ≥ 35o. Fig. 5b shows the influence of photonic stop band on emission of donor at different angles (thick lines) compared to its emission when stop band effect was absent (dotted lines). The dip observed in the emission band of Rh-B occurs because of reduced LDOS at that wavelength. Since, LDOS is an angle dependent property of PhC the emission spectra of embedded donor too changed with angles.3 When the stop band matched with emission maxima of donor (40o– 50o), the donor emission was effectively suppressed with simultaneous enhancement in acceptor emission intensity as compared to emission recorded at 10o. In this case, the concentration of acceptor was 10 times higher than the concentration of donor for this, ratio of integrated emission of acceptor to donor was found to be 0.64. This value is much higher than the value (0.16 from Fig. 4b) obtained in case of dye mixture solution for similar concentrations of acceptor and donor. This indicates efficient energy transfer from donor to acceptor occurred in PhC matrix.



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Fig. 6: Integrated emission ratios of acceptor to donor at different angles when dyed PhC was immersed in acceptor solution of concentration 0.5 mM , inset shows emission spectrum of crystal recorded at 20o (thin line) and at 42o (thick line) Fig. 6 shows the integrated emission ratio of acceptor to donor in PhC when concentrations of Rh-B and Rh-800 were 0.005 mM and 0.5 mM, respectively. Significant improvement in the ratio at angle ≥ 35o is a clear indication of energy transfer from D to A when photonic stop band entered within the emission range of donor. Inset of Fig. 6 shows a typical emission spectrum of dyed PhC placed in acceptor solution of concentration 0.5 mM recorded at 20o (thin line) and 45o (thick line). Inhibition in donor emission associated with enhancement in acceptor emission is clearly noticeable in this figure, establishing how emission intensity of Rh-800 exceeds that emitted by donor Rh-B.


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3.3 Lifetime measurements:

Fig. 7: Fluorescence decay curve for (a) Rh-B dye doped PhC in air (curve-1), PhC immersed in Rh-800 solution (curve-2), and (b) Rh-B in solution (curve-1) and dye mixture solution (curve-2), ‘IR’ is instrument response function

Curve-1 in Fig. 7a is the fluorescence decay curve of Rh-B dye embedded in the PhC matrix. The fluorescence of implanted donor exhibits a bi-exponential decay with lifetime components (τi) 4.09 ns and 115 ps and pre-exponential factors (Bi) 0.72 and 0.28, respectively. The bi-exponential decay nature of Rh-B in PhC is attributed from subensembles of dye molecules undergoing different interaction with their environment. The longer decay component originated from Rh-B molecules being influenced by the presence of polystyrene matrix however, the shorter component is attributed to molecules undergoing some additional decay processes.36 The lifetime of the donor modified significantly in presence of Rh-800. The fluorescence decay of PhC in acceptor solution was bi-exponential with faster decay components 2.9 ns and 18.5 ps with pre-exponential factors 0.2 and 0.8, respectively. The decay trace of dye doped PhC in presence of acceptor is shown with curve2 in Fig. 7a. Quenching in lifetime of the donor in presence of acceptor signifies nonradiative energy transfer between Rh-B and Rh-800. For comparison, fluorescence decay profiles of Rh-B in absence (curve-1 in Fig. 7b) and in presence (curve-2 in Fig. 7b) of Rh15 ACS Paragon Plus Environment


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800 in ethanolic solution were also measured and found almost same as 2.78 ns and 2.68 ns, respectively. This indicates possibility of energy transfer between dyes in solution form is less. The instrument response function (labelled as IR) and the best-fit simulated decay curves (solid line passing through the exponential points) are also shown in Fig. 7a and 7b. The energy transfer efficiencies (η) from Rh-B to Rh-800 in periodic PhC and in dye mixture solution were calculated using following equation 37

= 1 −

(2)

where and are the average lifetime of donor in absence and in presence of acceptor, respectively, such that 〈〉 = ∑ and ∑ = 1 . The efficiency of energy transfer between D-A pair in PhC and in dye mixture solution are determined as 80 % and 4%, respectively.

Fig. 8: Ultrafast fluorescence decay of Rh-B dye doped PhC (solid circles) and dyed PhC immersed in Rh-800 solution (open circles), ‘IR’ is instrument response function. Inset shows the magnified spectra.


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Solid and open circles in the Fig. 8 are the ultrafast fluorescence decay traces of Rh-B doped PhC and dyed PhC immersed in the acceptor, respectively. For both cases, the decays were four-exponential; the best-fit simulated curves are shown with solid lines in Fig. 8. Clear quenching in donor lifetime in presence of the acceptor is noticeable in the image. The decay components for Rh-B dye doped PhC are 0.5902 ps, 6.29 ps, 71.85 ps, and 4010 ps with pre-exponential factors -0.12 %, 0.59 %, 12.78 %, and 86.75 %, respectively. In presence of acceptor, the decay components were comparatively faster and are; 0.2486 ps, 3.8878 ps, 40.4859 ps, and 2900 ps with pre-exponential factors -0.05 %, 0.33 %, 3.73 %, and 95.99 %, respectively. This quenching in donor lifetime clearly indicates energy transfer from donor to acceptor. There are three advantages associated with the PhC which play important role in improving the energy transfer efficiency between dyes, (a) increased spectral overlap between donor emission and acceptor absorption in PhC (Fig. 3b), (b) increased proximity of acceptor and donor molecules within PhC facilitating effective energy sharing between D and A, and (c) increased time spent by de-excited photons trapped inside PhC structure because of restricted LDOS. When photonic stop band and emission band of the donor overlap photons generated through de-excitation of optically pumped donor are prohibited from propagating through the structure and hence remain trapped within the PhC. All these mechanisms boost probability of energy transfer between donor and acceptor in PhC in comparison to a dye mixture solution. Complete quenching of donor emission was not expected in present system, because the void sizes ( ~ 33 nm and ~ 62 nm) in the PhC were greater than the defined length (1-10 nm) within which the non-radiative energy transfer occurs. Therefore, the donor molecules were partially quenched by the acceptor molecules and some of the donor did not have a nearby acceptor to share energy.34



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Conclusion:

Good quality self-assembled PhC were synthesized and fluorescence resonance energy transfer between Rh-B (donor) and Rh-800 (acceptor) was investigate in the periodic environment. A significant energy transfer between the fluorophores was observed for the angles where photonic stop band overlapped emission spectra of donor. The excited state lifetime of the donor reduced in the presence of acceptor and this confirmed fluorescence resonance energy transfer between the embedded dyes. The energy transfer efficiency was found to be ~ 80% in PhC. Our results show that PhC can serve as an efficient environment to enhance energy transfer efficiency between embedded laser dyes.

Acknowledgment: Sunita Kedia acknowledges the Board of Research in Nuclear Science (BRNS), DAE, Government of India for Dr. K. S. Krishnan Research Fellowship. Authors acknowledge Dr. S. Nath, Mr. A. K. Mora, and Dr. B. Nilotpal, RPCD BARC, for their help in lifetime measurements.

Supporting Information: Molecular formula of Rhodamine-B dye Molecular formula of Rhidamine-800 dye Schematic of FRET This information is available free of charge via the internet at http://pubs.acs.org


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[10] Noda, S.; Tomoda, K.; Yamamoto, N.; Chutinan, A. Full Three-Dimensional Photonic Bandgap Crystals at Near-Infrared Wavelengths Science 2000, 289, 604-606 [11] Miyake, M.; Chen, Y. C.; Braun, P.V.; Wiltzius, P. Fabrication of Three-Dimensional Photonic Crystals Using Multibeam Interference Lithography and Electrodeposition Adv. Mater. 2009, 21, 3012-3015 [12] Yan, Q.; Zhou, Z.; Zhao, X.S. Inward-Growing Self-Assembly of Colloidal Crystal Films on Horizontal Substrates Langmuir 2005, 21, 3158- 3164 [13] Kedia, S.; Vijaya, R.; Ray, A.K.; Sinha, S. Photonic Stop Band Effect in ZnO Inverse Photonic Crystal Opt. Mater. 2011, 33, 466 - 474 [14] Kubo, S.; Gu, Z. Z.; Takahashi, K.; Fujishima, A.; Segawa, H.; Sato, O. Tunable Photonic Band Gap Crystals Based on a Liquid Crystal-Infiltrated Inverse Opal Structure J. Am. Chem. Soc. 2004, 126, 8314-8319 [15] Smith, K. C. The Photobiological Basis of Low Level Laser Radiation Therapy Laser Theraphy 1991, 3, 19-24. [16] Blum, C.; Zijlstra, N.; Lagendijk, A.; Wubs, M.; Mosk, A. P.; Subramaniam, V.; Vos, W. L. Nanophotonic Control of the Forster Resonance Energy Transfer Efficiency Phys. Rev. Lett. 2012, 109, 203601-1-5 [17] Lebrun, M. C. C.; Prats, M. Fluorescence Resonance Energy Transfer (FRET): Theory and Experiments Biochem. Educ. 1998, 26, 320-323 [18] Sekar, R. B.; Periasamy, A. Fluorescence Resonance Energy Transfer (FRET) Microscopy Imaging of Live Cell Protein Localizations The journal of Cell Biology 2003,160, 629-633 [19] Gambin, Y.; Deniz, A. A. Multicolor Single-Molecule FRET to Explore Protein Folding and Binding Mol. BioSyst. 2010, 6, 1540-1547


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Figure Captions: Figure 1: SEM image of Rh-B doped PhC (a) hexagonal arrangement of micro-spheres on top surface of the crystal represent plane of face centered cubic lattice structure, and (b) cross-sectional view shows extent of closed packed layers in the crystal

Figure 2: Reflection (solid line) at 10o transmission (dashed line) at normal incidence spectra of PhC, inset is reflection spectra of PhC at different angles

Figure 3: (a) Normalized absorption spectra of Rh-B (solid line) and Rh-800 (dotted line) dyes in ethanol, and (b) Normalized emission spectra of Rh-B in solution (thick line), in PhC (thin line) at 532 nm excitation and absorption spectrum of Rh-800 (dotted line)

Figure 4 : (a) Emission spectra of D-A in dye mixture solution at 532 nm excitation with fixed donor concentration at 0.005 mM and acceptor concentrations 0.005 mM (thin line), 0.05 mM (dotted line), 0.5 mM (dashed line), and acceptor (thick line) alone at concentration 0.5 mM, and (b) ratio of peak intensities of acceptor to donor for different concentrations of acceptor

Figure 5:

Emission spectra of Rh-B doped PhC dipped in acceptor solution of

concentration 0.05 mM (a) at 10o (solid line), reflection spectra of PhC at 10o in air (thin line) and in ethanol (dashed line), and (b) at different angles (solid lines) and at 10o (dashed lines).

Figure 6: Peak intensity ratios of acceptor to donor at different angles when dyed PhC was immersed in acceptor solution of concentration 0.5 mM , inset shows emission spectrum recorded at 20o (thin line) and at 42o (thick line).

Figure 7: Fluorescence decay curve for (a) Rh-B dye doped PhC in air (curve-1), PhC immersed in Rh-800 solution (curve-2), and (b) Rh-B in solution (curve-1) and dye mixture solution (curve-2), ‘IR’ is instrument response function. 23 ACS Paragon Plus Environment


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Figure 8: Ultrafast fluorescence decay of Rh-B dye doped PhC (solid circles) and dyed PhC immersed in Rh-800 solution (open circles), ‘IR’ is instrument response function. Inset shows the magnified spectra.


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Table of Contents Image:



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Author Biographies:

Sunita Kedia completed her PhD in photonic crystal based micro-cavity lasers from Indian Institute of Technology, Bombay in 2011. She was a postdoctoral fellow in Theoretical Physics division at Physical Research Laboratory, Ahmedabad. She received Dr. K. S. Krishnan Fellowship from Department of Atomic Energy in 2013. Her research interests are study of Resonance energy transfer between chromophores in photonic band gap environment, femtosecond micromachining and laser treatment on bioactive glasses to enhance biocompatibility.

Sucharita Sinha has carried out extensive theoretical and experimental investigations on nonlinear optical phenomena in laser-atom interaction, photo-thermal properties of tunable-laser media and developed novel attractive means to improve the quality of high-average-power laser beams. She received her Ph.D degree in Physics from Mumbai University in 1990 for her work on Optically Pumped Molecular Gas Lasers. Her work on theoretical analysis of quantum size effects in composite materials and semiconductor nanospheres resulting in tailored optical absorption spectrum is widely cited in literature. Among her current research interests, in the field of laser material ablation process she has demonstrated a unique dry laser etching technique required for metallographic examination of nuclear fuel pellets, and laser based surface micro-structuring of electron emitters leading to vastly improved field-emission properties.


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Influence of Photonic Crystal on Fluorescence Resonance Energy

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