Multifunctional Reversible Fluorescent Controller Based on a One

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A multi-functional reversible fluorescent controller based on one dimensional photonic crystal Yuxin Wu, Huaizhong Shen, Shunsheng Ye, Dong Yao, Wendong Liu, Junhu Zhang, Kai Zhang, and Bai Yang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b09650 • Publication Date (Web): 27 Sep 2016 Downloaded from http://pubs.acs.org on September 30, 2016

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ACS Applied Materials & Interfaces

A multi-functional reversible fluorescent controller based on one dimensional photonic crystal Yuxin Wu, Huaizhong Shen, Shunsheng Ye, Dong Yao, Wendong Liu, Junhu Zhang, Kai Zhang*, Bai Yang State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012 (P. R. China) KEYWORDS: one dimensional photonic crystal, fluorescent controller, multi-functional, pH responsive, quantum dots

ABSTRACT

With the aim to build multi-functional solid fluorescent controller, one dimensional photonic crystal and CdSe fluorescent single layer were separated on the opposite side of quartz substrates. The separation structure remarkably facilitates materials selection for the fluorescent controller, which allows to freely choose the fluorescent substance and constituents of 1DPC from a wild range of available materials with the best desirable properties and without caring about the interactions between them. Fluorescent enhancement and weaken effect were successfully achieved when the excitation light was irradiated from different sides of the fluorescent device. In addition, the fluorescent intensity can be altered reversibly along with environmental pH values according to the change of a pH-responsive one dimensional photonic

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crystal layer, which is quite different from previous reported quenching mode. Meanwhile, the original position of photonic stop band is essential to decide the pH value where the best effect of fluorescent control. It provides a way to adjust the effect of fluorescent controller according to certain applied situation. The mechanism of fluorescent variation was confirmed by the assist of finite-difference time-domain simulation. Furthermore, this device is also able to modulate fluorescent wavelength and full width at half maximum by overlapping the photonic stop band and the emission of CdSe. Therefore, this method offers a universal strategy for the fabrication of fluorescent controllers.

1. Introduction As manipulating solid fluorescence (FL) has derived merits in improving the efficiency of practical applications such as sensor, lighting device and optoelectronic equipment, majority of developmental reports focus on the synthesis and modification of FL substances. Meanwhile, utilizing an external structure platform to tune FL has also aroused more and more interests for their universality. Surface plasmon resonance (SPR) and fluorescence resonance energy transfer (FRET)1,

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are common approaches for the manipulation of FL. Though these methods are

effective and widely used, there are still drawbacks such as complicated experimental processes and limited tuning effect. For these reasons, photonic crystal (PC) is an attractive alternative for FL manipulation3, 4. Photonic crystal, a periodic nanostructure with alternative arrangement of at least two constituents, can manipulate the propagation of photons in a similar way that semiconductors control electrons.5 The intrinsic characteristic of PC is the forbidden band, a spectral range of intense reflectivity, known as a photonic stop band (PSB). Among various of PCs, one


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dimensional photonic crystal (1DPC) has aroused great attention for the simplest PC structures and various functions6. In 1DPCs, layers of materials with different refractive index were alternatively modulated along one direction and the multiple functions depend on diverse composite materials and tunable optical properties. The optical properties of 1DPCs are influenced by the refractive index of constituent materials used, thickness of layer, incident angle and the number of layers7. Benefited from different stimuli-responsive polymers8 adopted, various of 1DPCs can perform specific response to humidity9, chemicals10, infrared light (IR)11, electricity12, magnetism13 etc. Besides, the hybridization between polymers and inorganic materials has provided more possibilities for developing materials diversity, functional variability, and structural stability, which significantly promote the practical applications of 1DPCs14-16. Up to now, the PSB, photonic band edge and photonic band gap of PCs have been utilized for the manipulation of FL17, 18. For example, Lei Jiang and coworkers. have reported the amplified FL by utilizing PSB of face-centered cubic PC to enhance the sensitivity toward trinitrotoluene (TNT)19 and metal ions20. Hernán Míguez fabricated an optical resonator for pressure sensing by tuning the matching degree between resonant or forbidden modes and the emission lines, which makes the luminescence being strongly modulated21. Ozin's group has achieved a narrow-band and monochromatic dye laser by utilizing blue edge of the PSB to overlap the R6G spontaneous emission22. The above-mentioned structures, however, either involve the infiltration of FL materials into PCs or use FL materials as a part of composition blocks of PCs. This kind of design is relatively complicated since it need carefully select the polarity and solubility of constituent materials in PCs or modify the surface of FL substances to make them


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inter-miscibility and preserve their own optical properties respectively. For these reasons, a facile and universal method to manipulate FL by external platform is highly desired at present. In this paper, we propose a universal method for the fabrication of the FL controller devices with a new architecture in which 1DPCs and FL materials are modulated on the different sides of a quartz substrate separately. In such way, one can choose the 1DPC materials and FL materials freely, without considering their solubilities or polarities. Herein, we choose CdSe quantum dots (QDs) as the FL source because of their widely use in the areas of light-emitting diode (LED)24, solar cell25 and biomarkers26. When the incident light was irradiated from 1DPC side of the substrate, the FL intensity of CdSe decreases due to the weaken of excitation light. While, CdSe FL were enhanced if the incident light irradiates from CdSe layer side since the incident light reflected by PSB was as second excitation light of CdSe. The FL can be further manipulated continuously and reversibly by choosing pH-responsive materials as a component for the 1DPCs. In addition, tuning the PSB location allows to change both FL peak position and full width at half maximum (FWHM) accordingly. As a result, a mult-functional FL controller has been realized. 2. Experimental 2.1

Materials

(N,N)-Dimethylaminoethyl methacrylate (DMAEMA, 99.5%), ethylene dimethacrylate (EGDMA, 98%) were purchased from Aladdin and were stored at 4℃. Polymethylmethacrylate (PMMA, Mw=120,000 g/mol) and azodiisobutyronitrile (AIBN) were obtained from Aldrich and AIBN was recrystalized twice in 95% ethanol before use. Chloroform, isopropanol (IPA), tetrabutyl titanate, HCl, Na2PO4•12H2O, and citric acid were used as received without further


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purification. The quartz plates with the thickness of 1 mm were cut into 2 cm × 2 cm pieces, soaked in a boiling piranha solution (a mixture of 98 wt% H2SO4/30 wt% H2O2 with a volumetric ratio of 7: 3) for 20 min (caution: strong oxide), then rinsed with deionized water and alcohol successively several times, stored in ethanol lastly, and dried with N2 stream before use. Polydimethylaminoethylmethacrylate (PDMAEMA) was prepared via solution radical polymerization. Briefly, 4.0 mL DMAEMA, 800 µL EGDMA, and 20 mg AIBN were dissolved in 50 mL chloroform in a sealed round-bottom flask. Then, the whole system was kept under nitrogen at 60 °C for 6 hours. CdSe was chosen as the FL substance and prepared by following a recipe thoroughly described elsewhere27. The titania sol (TiO2) was prepared according to the reference 28. Briefly, 4 mL tetrabutyl titanate was dissolved in 2.0 mL IPA in a conical flask for 5 min. The mixture of 210 µL water, 17 µL concentrated HCl and 4.0 mL IPA was ultrasonic treated for 5 min. The mixture solution was dripped into the above conical flask over 10 min, and the resulting solution was stirred for 12 h at room temperature. Mixed acid-base buffer solutions at the range of pH 2.2-7.0 were used, and the pH was adjusted to the desired value with different volume of 0.2 M Na2HPO4 and 0.1 M citric acid aqueous solution (as described in Table S1). 2.2

Fabrication of fluorescent controller

A pH-sensitive FL controller was fabricated by alternately spin-coating TiO2 sol and the PDMAEMA at 3000 rpm for 1 min on one side of a quartz substrate. The TiO2 layer was baked at 100 °C for 10 min and the polymer layer was baked at 135°C for 10 min. To guarantee the same optical property of both sides of photonic crystals, the first and the last layer were TiO2 layers in all the cases. The thicknesses of TiO2 and PDMAEMA layers were tuned by the control of their concentrations in IPA and chloroform solutions, respectively. The CdSe QDs (0.1mol/L,


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1 mL) were dispersed in PMMA/toluene solution (0.1 g/mL, 2 mL) and were spin-coated on the opposite side of the substrate at 1000 rpm for 1 min. 2.3

Characterization

Scanning electron microscopy (SEM) images were recorded with a JEOL FESEM 6700F electron microscope at an accelerating voltage of 3 kV. The samples were sputtered with a thin layer of Pt prior to imaging. Transmission electron microscope (TEM) micrographs were recorded with a Hitachi H-800 electron microscope with an accelerating voltage at 200 kV. The angle-dependent specular reflection was evaluated using spectrometer from 200 to 1000 nm consisting of a collimated beam of a fiber-coupled tungsten-bromine lamp (Ocean Optics DT1000CE) and a goniometer (Rigaku), adopting Maya 2000 Pro detector. FL spectroscopy was performed with a Shimadzu RF-5301 PC spectrophotometer. The pH values of the buffer solution were confirmed using a pH meter (Sartorius, Professional Meter PP-5V). Digital camera photographs were shot by Canon Powershot G1X with a commercial fiber laser (470 nm) irradiation. The calculated reflectance spectra and electric field were obtained using the commercialized software package, FDTD Solutions (Lumerical 20 Solutions, Inc., Canada). We set the layer thicknesses and refractive indexes of the simulation models according to corresponding samples. The thicknesses of PDMAEMA and TiO2 were determined by using a Dektak 150 surface profiler (Veeco). The refractive indices of the polymer thin films at the wavelength of 632.8 nm were measured on an AUEL-III auto45 laser ellipsometer equipped with a He-Ne laser (λ = 632.8 nm). The thicknesses were verified via SEM cross-sectional images. 3. Results and Discussion 3.1

Building of fluorescent controller


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A schematic illustration of the FL controller is shown in Figure 1. The responsive FL controller was obtained by preparing the 1DPC ([PDMAEMA/TiO2]6.5, where 6.5 represents the number of bilayers) on one side of a quartz substrate and the FL layer (CdSe/PMMA) on the opposite side. From the illustration, the light source and detector were located on the same side of the device and perpendicular to each other. A monochrome (470 nm) light was adopted as excitation light with an incident angle of 30°. The excitation wavelength was selected according to the absorption wavelength of CdSe (Figure S2a) and the availability of light source. The incident and detection angles were resulted from the instrument structure. This schematic gives a situation that incident light comes from 1DPC via quartz substrate to CdSe successively as example (which is defined as front side). In fact, the light can also be illuminated from the CdSe side (back side). 3.2

pH responsive behavior of 1DPCs

In this work, the PDMAEMA is responsive to pH, which guarantees the device is to be pH adjustable. First of all, the pH responsive behavior of 1DPC was studied. The 1DPC with 6.5 bilayers was fabricated on the quartz substrate with TiO2 gel as the first and last layers. The cross-sectional SEM images of the 1DPC are shown in Figure 2a. The TiO2 layers are brighter than the polymer layers because of their higher electron density. It can be seen that the interfaces between the different layers are very sharp, which insured the good optical quality of the 1DPC structure. Then, the 1DPC was immersed in buffer solution (from pH=7.0 to 2.2) and reflectance spectra were monitored from both front side and back side (quartz side) of the device as shown in Figure 2b. Three pH values were chosen to demonstrate the adjustability of the device. Figure


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S1a shows the PSB red-shifted from 550 nm to 720 nm gradually when the pH decreased from 7.0 to 2.2. According the Bragg formula, that is

2 2 mλ Bragg = 2 D neff - sin θ

From the equation, m represents the diffraction order, besides, the PSB peak position (λBragg) is proportional to the efficient refractive index (neff) and the thickness of a bilayer (D), but inversely proportional to the incident angle (θ)29. Upon decreasing the pH value, the PDMAEMA layers swelled significantly due to the electrostatic repulsion between the protonated amino groups in PDMAEMA30. The thicknesses of PDMAEMA layers resulted in the PSB peak position to shift to longer wavelength according to the Bragg equation (Figure 2b). In addition, under the same pH conditions (Figure 2b and S1a), the variations of PSB peak positions and reflectance intensity of 1DPC were ignorable when the excitation light was irradiated from either the front or back sides of substrate, which suggests the symmetrical structure of 1DPC and the excellent transmittance of the quartz substrate (Figure S5). As for the FL controller device, when incident light irradiates from CdSe side, the reflectance spectra are not exact owing to the absorption of QDs. However, the reflectance spectra can be monitored from the 1DPC side instead of CdSe side. Furthermore, Figure S1b indicates that the peak positions of the transmittance and reflectance spectra of the 1DPC were the same and had the same shifting trend with the change of pH values. In addition, for 1DPC the incident light is almost the summation of reflectance and transmittance parts, which is proved by the mirror effect between the reflectance and transmittance spectra (Figure S1b). Therefore under a certain incident light, the transmittance


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intensity decreases with the increase of the reflectance intensity. For the FL controller device with the 1DPC and CdSe on the opposite sides, the transmitted light was efficient to excite CdSe. But the exact transmittance spectra of the 1DPC is difficult to measure due to the absorption and reflectance of the CdSe layer. Therefore, only the reflectance spectra of the controller device were monitored in the following study. In addition, the PSB positions of the device showed remarkable consistency during 15 cycles of the swelling-deswelling treatments by adjusting pH values (Figure 2c). This result indicates the excellent repeatability and stability of the 1DPC structure. The steady repeatable behavior demonstrated that the structure of 1DPC was well maintained during the swelling-deswelling process. To make the 1DPC return to the original state, the device was immersed in deionized water for several hours. Then the amino groups in PDMAEMA were deaprotonated under the osmotic pressure and ion balance31. Thus the electrostatic repulsions among the polymer chains decreased. And then 1DPC was heated in 60℃ oven for hours after every detection process to expel all the water out. 3.3

CdSe layer stability

In order to investigate the stability of the CdSe/PMMA layer, the CdSe/PMMA solution was spin-coated on a quartz substrate without 1DPC layers on the opposite side. The FL spectrum of the CdSe/PMMA thin film with an emission peak at 580 nm is shown in Figure S2b. The TEM study revealed that the CdSe QDs were well-dispersed in the PMMA layer (Figure S2c), that is, no aggregation of CdSe QDs was observed. Therefore, the FL property of the CdSe QDs was well preserved in the PMMA layer. In addition, the low water permeability of the hydrophobic PMMA matrix can also protect the CdSe QDs from the buffer solutions23. Both the PL intensity


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and peak position showed negligible changes upon pH treatments from 2.2 to 7.0 (Figure 3). The inset of Figure 3 displays the FL intensities of CdSe were constant at different pH (from 2.2 to 7.0). These results suggest the CdSe QDs can be well protected by PMMA matrix and their FL can't be influenced by the stimuli of the environmental pH. 3.4 The manipulation of fluorescent intensity The PSB position of the device was originally set at 410 nm (30 °). For pH below 7.0 the PSB overlapped with the excitation wavelength (470 nm) of the CdSe QDs, meanwhile, it caused little disturbance to their FL emission band at 580 nm (Figure 4a, red circle). Thus, the FL property of CdSe QDs is mainly dependent on the reflectance intensity of the 1DPC at their excitation wavelength (470 nm). As the reflectance intensity at 470 nm of the pH-responsive 1DPC changes with pH; therefore, the PL intensity of CdSe layer can be tuned accordingly. To evidence this hypothesis, the FL spectra were firstly measured from the front side of the device with the incident light irradiating from the front side (see 3.1 section for details). As indicated in Figure 4a, the reflectance spectra of the device showed the PSB was red-shifted from 410 nm to 490 nm after being immerged into different buffer solutions (from pH=7.0 to 2.2), and the corresponding FL intensity varied within the scope of 361 to 547 counts (Figure 4b). Figure 4c summarized the reflectance intensity at 470 nm and PL intensity as a function of pH values. It can be seen that the FL intensity shows an opposite trend with the variation of reflectance intensity at different pH values. The FL intensity reached its minimum at pH of 3.0, when the PSB shifted to the excitation light wavelength at 470 nm and the reflectance was maximized. These changing processes were recorded by optical images (Figure 4d to f). It can be seen that the controller device with the treatment of pH=3.0 solution (Figure 4f) showed much weaker FL


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than that of the untreated device (Figure 4e) due to the different overlap of their PSB and the excitation wavelength of 470 nm. In addition, the device with only the CdSe layer, that is without the 1DPC (Figure 4d), showed much stronger FL compared to the other two devices. To sum up, when the incident light was irradiated from the 1DPC side of device, incident light was partly shielded by PSB, less incident light could transmitted through quartz and reached CdSe layer as excitation light, thus the FL of CdSe will be reduced. The manipulation of the FL of CdSe layer has been successfully achieved through the control of the overlap between the PSB of 1DPC and the excitation light for CdSe QDs by adjusting different pH values. The FL intensity showed an opposite trend with the variation of reflectance intensity and reached its minimum when the PSB was shifted to the excitation wavelength of 470 at pH of 3.0. We also studied the manipulation of FL with pH values when the incident light and FL detector were on the back side of the device with otherwise the same conditions. The trend of reflectance spectra with pH values (Figure 5a) was the same as Figure 4a owing to the same device was adopted. It should be noted that due to the direct irradiation of the incident light on the CdSe layer, the FL intensity was much stronger than that from the 1DPC side. Narrower slits of excitation and emission light were chosen to avoid to be out of the detection range. The exact FL intensity values (Figure 5b and c) measured with the incident light from the back side were stronger than those in Figure 4b and c under the same pH conditions. Contrary to previous scenario, the illumination of incident light from the back side resulted in that the FL intensity showed a same trend with the variation of reflectance intensity (Figure 5c). This result was attributed to the limit absorption of the CdSe thin film, which led to a fraction of the incident light to be transmitted through the film and reflected by the 1DPC. The reflected light can excite the FL of CdSe film again. Therefore, the trend of FL intensity was consistent with the


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reflectance intensity of the 1DPC, which is determined by its PSB position. Among different pH conditions, the PSB processed the best overlap with the excitation wavelength of 470 nm at pH of 3.0, resulting in the strongest reflectance intensity and consequently maximum FL intensity as shown in Figure 5b and c. Similar mechanism has been proposed by others.32 The optical image of the FL controller device after treated with pH=3.0 solution (Figure 5f) showed much brighter red FL compared the untreated one (Figure 5e), which is contrary to previous scenario. This result also suggests the FL intensities with the irradiation from opposite sides of the device yield the largest difference when the PSB has the best overlap with the excitation light. To demonstrate the manipulation of FL, we patterned the CdSe layer with a photolithography mask. Figure S3 shows digital color images of the device with the CdSe film patterned with "JLU" letters. It can be clearly seen that the FL intensity of the same device changed with different pH values and irradiation directions. Thus the FL of the controller device can be manipulated in multi-degrees. 3.5 The mechanism of fluorescent control In order to understand the mechanism, a model was established using finite-difference time-domain (FDTD) simulation as illustrated in Figure 6a. The structure consisted of air, 1DPC and quartz substrate as shown from top to bottom. Based on the measuring results, the thickness of TiO2 layers was set as 49 nm. Two thicknesses of 72 nm and 91 nm were selected for de-swelled and swelled PDMAEMA layers, respectively. The simulated PSBs of 1DPC with de-swelled and swelled PDMAEMA were 400 nm and 450 nm, respectively (Figure S4), which shows a good agreement with the experimental results. The simulated reflectances at 470 nm for the 1DPCs with de-swelled and swelled PDMAEMA layers were 3.48% and 80.70%,


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respectively. When incident light (470 nm) from the front side (Figure 6b and 6c), the electric intensities of two devices both decayed from incident plane to substrate bottom and oscillated several times throughout the periodic structure. The electric intensities concentrated near the incident plane and the electric intensities of high-reflectivity device decreased more than low-reflectivity device. And on the bottom of substrate, electric intensity was weaker for the device with higher reflectivity. This dispersion was due to the manipulation of 1DPC on light. When PSB was closer to the incident light wavelength, reflectance intensity at excitation wavelength was more intense. 1DPC could prohibit the propagation of light, thus it localized excitation light near the incident surface. So excitation light intensity on the bottom of substrate (CdSe side) would be reduced. It was the reason for the weaker FL when PSB was 450 nm. This phenomenon was in agreement with experimental results. When excitation light came from bottom of the substrate (CdSe side), the electric intensities enhanced from air towards the substrate (CdSe side) (Figure 6d and Figure 6e). The most intense electromagnetic field was achieved on the bottom of the substrate. The same as before, the electric intensity was more intense when it was closer to incident light plane. And when reflectance intensity at excitation peak position increased, more electric field near incident plane would be enhanced and the difference in electric field became bigger in the whole structure. Thus FL substance would be excited more effectively, and the emission intensity would be more intense. The result is coincident with afore-mentioned FL manipulation mechanism. 3.6 The achievement of different fluorescent controller We have also analyzed the FL manipulation of a controller device with its original PSB almost at the excitation wavelength of 470 nm for the CdSe layer (Figure 7). As depicted in reflectance spectra (Figure 7a), the PSB was continuously red-shifted away from 470 nm when the pH of the


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buffer solutions was reduced from 7.0 to 2.2. The FL intensities with the incident light from either the front side (Figure 7b) or the back side (Figure 7d) of the device increased or decreased monotonically with the decrease of pH, respectively. The variation tendencies of FL and reflectance intensities with pH are different for the incident light irradiated from the front (back) side of device (Figure 7c, 7e), which is consistent with the result mentioned above. Differently, the best effect of manipulation located at pH=7.0 value. Controlling the condition of FL state endows the device with the ability to adapt to different specific situations. 3.7 Manipulation of other emission properties by utilizing 1DPC The above sections have studied the effects of the PSB and the excitation light position on the FL intensity of the controller device. To explore the direct interaction between 1DPC and FL emission, the PSB was originally tuned to 469 nm (incident angle was equal to 60°). The variation of incident angle is because PSB overlapped with the FL emission rather than the excitation light when it was irradiated from 1DPC with 30°angle. Thus, to analyze the effect of 1DPC on FL, the CdSe emission was regarded as incident light and its relative position with 1DPC formed 60°angle. According to Figure 8a, PSB red shift from 469 nm to 524 nm with pH decreasing and gradually approached the FL emission scope. When the light irradiates from 1DPC, both of the peak position and full width at half-maximum (FWHM) of the FL emission spectra changed. With pH reducing, the intensity of short-wavelength FL spectra decrease firstly and the longer-wavelength (>580 nm) FL keep stable until pH=3.0 (Figure 8b), which are represented as red-shift of emission peak position and broaden of FWHM. This phenomenon indicates that 1DPC could not only control FL emission intensity but also adjusted other FL properties. It is attributed to the overlap part between 1DPC and FL emission, the PSB prohibited


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this part of FL from reaching detector. The closer the PSB peak position and emission light wavelength, the more FL portion reduced. 4. Conclusion

In summary, a tunable FL controller was fabricated by preparing the 1DPC (PDMAEMA/TiO2) and CdSe FL layer on the opposite side of a quartz substrate. Benefited from the pH-responsive PDMAEMA layer, a pH-tuning FL device was obtained by the control of the relative position between the PSB of 1DPC and the excitation wavelength of CdSe layer. The manipulation effect can be directly read-out by naked eyes. The FL intensity also depended on the direction of the light irradiated from the front or back side of the device. By altering the original PSB, the pH effect of the brightest and darkest FL can be changed and the FL peak position and FWHM can be modulated as well. The approach we have presented is not limited to a CdSe QDs; thus, it can be universally applied to other FL materials as well. If a kind of wide FWHM FL substance is chosen, we suppose a colorful FL controller will be attained. In addition, the stimuli to trigger the controller can be various by utilizing other responsive polymers. We have proposed is a proof-of-concept and universal method for the fabrication of FL controllers for different situations.

FIGURES


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Figure 1. Schematic illustration of the FL controller and relative position of excitation light and detector.

Figure 2. (a) SEM images of the 1DPC with 6.5 bilayers on the quartz substrate. The scale bar is 1.0 µm. (b)Reflectance spectra measured from the front and reverse (quartz side) sides of the 1DPC in different pH solutions; (c) Reversibility of reflectance peak positions of 1DPCs switched between pH=2.2 buffer solution and deionized water (pH=7.0) over 15 cycles.


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Figure 3. FL spectra of the CdSe/PMMA thin film in different pH buffer solutions, and the inset: FL emission intensities at different pH values (excitation wavelength of 470 nm).


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Figure 4. (a) Reflectance spectra and (b) FL spectra of device after dipping into different pH buffer solutions. (c) Reflectivity at excitation light wavelength (470 nm) and PL intensity as a function of pH values; and the digital photos of the CdSe monolayer under (d) a bare quartz, (e) the original device, and (f) the device after dipping in pH=3 solution illuminated by a 470 nm laser. Scale bar =1.0 cm.


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Figure 5. (a) Reflectance spectra and (b) FL spectra of device after dipping into different pH buffer solutions. (c) Reflectivity at excitation light wavelength (470 nm) and PL intensity as a function of pH values; and the digital photos of the CdSe monolayer under (d) a bare quartz, (e) the original device, and (f) the device after dipping in pH=3 solution illuminated by a 470 nm laser. Scale bar =1.0 cm.


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Figure 6. (a) The model structure for the FDTD simulation (chromatic scale bar represents the refractive index). Simulated electromagnetic field distributions along the y-direction of the proposed 1DPC with PSB peak positions at 400 nm (b and d, incident from air and quartz sides, respectively) and 470 nm (c and e, incident from air and quartz sides, respectively). The chromatic scale bars of these four figures represent the electromagnetic field intensity.

Figure 7. (a) Reflectance spectra of the device treated with different pH buffer solutions; (b) and (d) FL spectra of device after dipping into different pH solutions when excited from

1DPC and


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CdSe side of the device, respectively; variations of reflectance at the excitation light wavelength (470nm) and the FL intensities of the device as a function of the pH values for excitation light (470 nm) from (c) 1DPC and (e) CdSe side.

Figure 8. (a) Reflectance spectra of the device (original peak position of 469 nm with an incident angle of 60 °) after dipping into different pH buffer solutions and (b) the corresponding FL spectra of the device excited with a excitation light of 470 nm from its front side.

ASSOCIATED CONTENT Supporting Information. The whole 1DPC optical properties (reflectance spectra and transmittance spectra) varying with pH. CdSe’s layer intrinsic properties. And optical images of device with different PL intensity. Also, the simulation spectra calculated by FDTD (PDF).This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author E-mail: [email protected].


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Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ACKNOWLEDGMENT This work was financially supported by the National Science Foundation of China (NSFC) under Grant No. 51433003, 51373065, 91123031, 81320108011, and the Specialized Research Fund for the Doctoral Program of Higher Education (SRFDP) under Grant No. 20130061130010. REFERENCES (1)

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Multifunctional Reversible Fluorescent Controller Based on a One

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