Postsynthetic and Selective Control of Lead Halide Perovskite

Sep 19, 2016 - The dashed line in Figure 1a shows the absorption spectrum of the CH3NH3PbBr3 microplate (see Experimental Section and Figure S1). ...
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Letter pubs.acs.org/JPCL

Postsynthetic and Selective Control of Lead Halide Perovskite Microlasers Nan Zhang,†,§ Kaiyang Wang,†,§ Haohan Wei,‡ Zhiyuan Gu,† Wenzhao Sun,† Jiankai Li,† Shumin Xiao,*,‡ and Qinghai Song*,† †

National Key Laboratory on Tunable Laser Technology, Department of Electrical and Information Engineering and ‡Department of Material Science and Engineering, Harbin Institute of Technology, Shenzhen, 518055, China S Supporting Information *

ABSTRACT: The control of photoluminescence and absorption of lead halide perovskites plays a key role in their applications in micro- and nano-sized light emission devices and photodetectors. To date, the wavelength controls of lead halide perovskite microlasers are mostly realized by changing the halide mixture in solution. Herein, we report the postsynthetic and selective control of the optical properties of lead halide perovskites with conventional semiconductor technology. By selectively exposing a CH3NH3PbBr3 microstructure with chlorine in inductively coupled plasma, we find that the wavelengths of absorption, photoluminescence, and laser emissions of exposed structures are blue-shifted around 50 nm. Most importantly, the device characteristics such as the photoluminescence intensities and laser thresholds are well maintained during the reaction process. We believe our finding will significantly boost the practical applications of lead halide perovskite based optoelectronics.

teristics are usually fixed and are hard to be modified again. Recently, a few postsynthetic control technologies have been recently studied with anion exchange in either solution or vapors.21−23 However, the first one usually happens within 1 s and is hard to be precisely controlled,21 whereas the latter one dramatically degrades the device performances, such as shortcircuit current density and the intensity of electroluminescence.22 Most importantly, to integrate the single-crystal perovskite microdevices into on-chip photonic circuits11 and to generate nanodevice arrays with uniform functions,24 it is essential to selectively tailor the absorption, emission, and other properties (such as refractive index) of a single device in submicrometer or nanoscale. Therefore, it is highly desirable to develop a simple and controllable technique to postsynthetically control the microlasers while primarily maintaining their device characteristics. Herein, we demonstrate a simple technique to postsynthetically control the absorption and emission properties of lead halide perovskite. Using a standard semiconductor technology, we show for the first time that the absorption, PL, and lasing wavelengths of single crystalline CH3NH3PbBr3 microplate can be widely tuned with precise control in both the spectral and spatial positions. Most importantly, the PL and lasing characteristics of lead halide perovskite based devices are well preserved during the reaction processes. The first step toward controlling the PL and laser emissions of lead halide perovskites is the synthesis of high-quality single

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he lasing actions in lead halide perovskite microwires and microplates have been intensively studied in the past two years.1−17 Because of their relatively long carrier lifetime, diffusion length, and low defect density, single crystalline lead halide perovskites have shown very high optical gain and large external quantum efficiency.3,4 Meanwhile, their high refractive indices and ultrasmooth facets can trap light well via either endfacet reflection [for Fabry−Perot (FP) lasers]4−8 or total internal reflection [for whispering gallery (WG) like lasers].9−14 Consequently, lasing actions have been successfully observed in lead halide perovskite microwires, nanowires, and microplates by either single-photon excitation or two-photon pumping.5 To date, the record low threshold around 220 nJ/cm2 (ref 4) and record high quality (Q) factor over 500014 have been demonstrated at room temperature. Unidirectional laser emissions have recently been reported in waveguide-connected lead halide perovskite microdisks.15 All of these laser characteristics are even comparable to classical covalent semiconductor lasers such as gallium arsenide microdisk lasers.18−20 Remarkably, the lead halide perovskites show extremely broad wavelength tunability based on stoichiometry.2 Through a simple mixing of different amounts of methylammonium iodide, bromide, or chloride in the precursor solution, the lasing wavelengths can be tuned from near-infrared to blue or ultraviolet in single crystalline lead halide perovskite microstructures. All of the above unique properties make lead halide perovskites ideal for lasing. The wavelength control in lead halide perovskite is mostly realized during the synthesis process. Once the single crystalline devices such as microwires and microplates are synthesized, their absorption, photoluminescence (PL), and lasing charac© XXXX American Chemical Society

Received: August 6, 2016 Accepted: September 19, 2016

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DOI: 10.1021/acs.jpclett.6b01751 J. Phys. Chem. Lett. 2016, 7, 3886−3891

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The Journal of Physical Chemistry Letters

partially replace Br− with Cl− and thus change the chemical composition and the corresponding emission wavelength. In our experiment, we have placed the CH3NH3PbBr3 microstructures into inductively coupled plasma (ICP, Oxford PlasmaPro System 100 Cobra ICP 180) and exposed them with chlorine. Here we keep the pressure of chlorine at 5 mTorr and the ICP power at 400 W (see Experimental Section). Figure 1c shows the measured absorption (dashed line) and PL (solid line) spectra after reaction in ICP for 60 s. While the CH3NH3PbBr3 microplate is the same one and no obvious damages can be seen in SEM image, the absorptive band edge shifts to 503 nm, and the center wavelength of the PL emission also changes to around 493 nm. The wavelength shifts of absorption and PL are both around 50 nm. The XRD spectrum is shown in Figure 1d, which is very close to Figure 1b. This indicates that the crystal structure of the microplate is primarily maintained during the postsynthetic control. Figure 2a illustrates the detailed impacts of reaction in ICP on the optical properties of lead halide perovskites. Here the

crystalline perovskite microstructures. Considering the potential applications of lead halide perovskite in green gap region, here we synthesized CH3NH3PbBr3 perovskites with a one-step solution-processed precipitation method (see Experimental Section).5,11 This synthesis method can generate a large number of high-quality, single crystalline CH3NH3PbBr3 microwires and microplates,14,15 which are sufficient to support both FP lasers and WG lasers. In this experiment, we selected one microplate to study its corresponding optical properties. The corresponding scanning electron microscopy (SEM) image is shown as the inset in Figure 1a. The length, width, and

Figure 1. Influences of ICP reaction. Panels a and c are the absorption (dashed line) and photoluminescence (solid line) spectra before and after reaction in ICP. Panels b and d are their corresponding XRD spectra. The inset in panel a is the top-view SEM image of the sample where the scale bar is 50 μm.

thickness of the microplate are 49 μm, 20 μm, and 297 nm, respectively. The dashed line in Figure 1a shows the absorption spectrum of the CH3NH3PbBr3 microplate (see Experimental Section and Figure S1). A clear absorption band edge can be seen at 550 nm. All these results are consistent with previous reports.5,8,9 The solid line in Figure 1a is the corresponding PL spectrum, which is obtained by pumping the microplate with a frequency-doubled Ti:sapphire laser (see Experimental Section and Figure S2). It is a broad peak centered at 542 nm with a full width at half-maximum (fwhm) around 30 nm. Figure 1b shows the X-ray diffraction (XRD) spectrum of the synthesized microstructures. All the XRD peaks are consistent with previous reports and can be indexed to the single crystalline cubic phase of CH3NH3PbBr3 perovskites.11,15 It is worth noting that the perovskite thickness and planar dimensions remain constant during the ion exchange reaction in the ICP chamber, as shown in Figure S3. Then we started to control the PL and absorption of the CH3NH3PbBr3 microplate. In conventional methods, the wavelengths of emission and absorption can be tuned via varying the halide mixture in lead halide perovskites.3,21−23 Considering the possibility of combining lead halide perovskite with conventional semiconductor technology, here we study the possible interaction between single crystalline CH3NH3PbBr3 microstructure and the chlorine gas or plasma. As pointed out by Eames et al, lead halide perovskites are mixed ionic−electronic conductors.25 Consequently, it is possible to

Figure 2. Postsynthetic control of PL and absorption. (a) PL (solid line) and absorption spectra (short dash−dot line) of microplate as a function of reaction time. (b) Dependences of PL wavelength (spheres), absorption band edge (triangles), and integrated output intensity (squares) on the reaction time. Here the pumping density is fixed at 2.71 μJ/cm2. (c) Changes of chemical composition in lead halide perovskite microplate.

results are taken from another microplate with thickness around 742 nm. With the increase of reaction time from 0 to 60 s, both the absorption and photoluminescence shift to shorter wavelengths. Figure 2b summarizes the PL central wavelength and absorption band edge as a function of reaction time. We can see that both the absorption and PL are almost linearly dependent on the reaction time. The slope of decrease is around −0.75, and total wavelength shift is almost 50 nm. Following the previous studies on solution-processed wavelength control, the changes in absorption and emission wavelengths usually relate to the modifications on the halide composition in lead halide perovskite. Here, because the lead halide perovskite microplate was exposed with chlorine in ICP, the wavelength shifts in PL and absorption might also be attributed to the changes in chemical composition. Further anion exchange with reaction time past 60 s could be observed. However, the severe degradatioin of PL intensity and decreased wavelength shift discount the importance and practicability of the proposed method. 3887

DOI: 10.1021/acs.jpclett.6b01751 J. Phys. Chem. Lett. 2016, 7, 3886−3891

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The Journal of Physical Chemistry Letters To confirm the changes in chemical composition, we carried out energy-dispersive X-ray spectroscopy (EDS) analysis. The ratio of Br/Pb in as-grown samples is around 75/25, which is consistent with a PbBr3 stoichiometry. After the samples are exposed in chlorine in ICP for 60 s, the ratio of Br−/Pb2+ changes to around 59.1/25, whereas the ratio of Cl−/Pb2+ increases from 0 to 15.2/25. Figure 2c shows the percentages of Br− and Cl− in perovskite microplate as a function of reaction time. Here all the reaction conditions are the same as those in Figure 1c. With the increase of reaction time, we can see that the percentage of Br− decreases linearly, whereas the percentage of Cl− increases linearly. Meanwhile, the ratio of (Br− + Cl−)/ Pb2+ in CH3NH3PbBr3 microplate is well maintained at around 3 (squares in Figure 2c). These results, associated with the XRD results, clearly show the replacement of Br− with Cl− during the reaction in ICP. Thus, the blue shifts of emission and absorption wavelengths can be simply attributed to the variation of halide mixture in lead halide perovskite. Then the intriguing question becomes how the Br− is replaced by Cl− in the single crystalline microplate. Within the lead halide perovskites CH3NH3PbX3, the significant equilibrium concentration of X−, Pb2+, and CH3NH3+ vacancies can support vacancy-mediated diffusion at room temperature.25,26 As the chlorine is ionized into Cl− in ICP, it is natural for us to consider the possible ion-implanting process or anion exchange. When Cl− ions reach the single crystalline, Br− will be simply replaced or exchanged with Cl− and the composition in the CH3NH3PbBr3 microplate is changed. One may argue that the substitution reaction between chlorine gas and Br− can also modify the halide composition and change the emission wavelengths.22,23 To exclude this possibility, we have done a control experiment by reducing the ICP power to 0 (see Figure S4). In this case, the chlorine is gaseous and is similar to that in previous reports.22 After placing a CH3NH3PbBr3 microplate into 10 mTorr chlorine gas for 30 s at 5 °C, we can still see the slight blue shift of the photoluminescence. However, the PL intensities have also been reduced. In addition, the lasing actions in the microplate have been eliminated by the reaction with Cl2. This shows that the chlorine gas can not only exchange the anion but also degrade the emissions, consistent with the previous report.22 Therefore, we know that the chlorine ions instead of chlorine gas play a key role in the postsynthetic wavelength control in Figure 2. We note here that the ICP power is very important in this technique. When the power is low, the wavelength shift is much smaller and the PL intensity is degraded. If the ICP power is higher than 500 W, the physical process can also damage the CH3NH3PbBr3 microplate (Figure S5). In additional to the wavelength shift, another important feature about ICP-processed perovskite microplate is that the integrated intensities of PL spectra are well maintained during the reaction process (squares in Figure 2b). This indicates that the developed wavelength control technique can also be used to tailor the laser emissions from lead halide perovskite devices. Associated with the PL experiment, the lasing actions of the microplate in Figure 2 have also been studied by increasing the pumping density. All the results are summarized in Figure 3. Before the reaction in ICP, we can see the transition from a broad PL peak to a sharp laser peak around 555 nm (Figure 3a). The corresponding fluorescent microscope image (the inset in Figure 3a) shows two bright spots at the facets of the microplate, indicating the formation of transverse WG laser9 in

Figure 3. Postsynthetic control of the lasing actions. (a) Emission spectra at different pumping conditions. The inset shows the microscope image of microplate above lasing threshold. (b) Dependences of output intensity and line width on pumping density. The inset shows the polarization of the microlaser. (c) Laser spectra from the same CH3NH3PbBr3 microplate after different reaction times. Here the pumping density is fixed at 3.75 μJ/cm2. (d) Lasing wavelength (spheres) and threshold (squares) of perovskite microplate laser as a function of reaction time.

the plane perpendicular to the substrate plane (see Figure S6). The lasing behavior (spheres) can be more clearly seen in Figure 3b, where the output intensity is plotted as a function of pumping density. With the increase of pumping density, the output intensity changes slowly at the beginning and increases dramatically once the pumping density is above 3.4 μJ/cm2. The dependence of fwhm on the pumping density is summarized in Figure 3b (squares). When the pumping density is above 3.4 μJ/cm2, the laser line width dramatically reduces to 0.33 nm, which is about 2 orders of magnitude smaller and gives a Q factor around 1667. The superlinear behavior of integrated output intensity and the reduction in fwhm as a function of pump density in Figure 3b well confirm the lasing actions in microplate. As shown in the inset of Figure 3b, the polarization is transverse magnetic (TM) mode with dominant magnetic field polarized perpendicular to the wave propagation direction in the transverse plane perpendicular to the substrate plane. As pointed out by Zhu et al.,4 the polarization of the lasing modes is determined by the waveguide mode. The waveguide modes are of hybrid nature with both weak longitudinal electric and magnetic components. Figure 3c shows the evolution of laser spectrum from the CH3NH3PbBr3 microplate with the increase of reaction time from 0 to 60 s. We can see that the laser peak gradually shift from 554.9 nm (original) to 544.5 nm (10 s), 533.8 nm (20 s), 527.6 nm (30 s), 521.2 nm (40 s), 512.9 nm (50 s), and 506.3 nm (60 s). The spheres in Figure 3d summarize the dependence of lasing wavelength on the reaction time. The blue shift is also quite linear, and the total wavelength shift is around 50 nm, consistent with the changes of PL and absorption well. The squares in Figure 3d show the thresholds of the microplate laser after different reaction time (see the details about the thresholds and spectra in Figure S7). When the reaction time in ICP is below 60 s, no obvious increase in laser threshold can be found. This is also well consistent with the changes in PL intensity (see Figure 2b). Actually, some thresholds after reaction in ICP are even lower than the original 3888

DOI: 10.1021/acs.jpclett.6b01751 J. Phys. Chem. Lett. 2016, 7, 3886−3891

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The Journal of Physical Chemistry Letters microplate laser. A similar phenomenon has also been observed in the PL. These results clearly show that the ICP can effectively tune the emission wavelengths without degrading their output intensities and thresholds. Figure 3 illustrates that the lasing wavelength of the CH3NH3PbBr3 microlaser can be tuned by the reaction time in ICP. Consequently, this technique can be used to generate a microlaser array in which each module has different reaction time in ICP and thus has different lasing wavelengths. One example is shown in Figure 4a, where three lead halide

Figure 5. Selective postsynthetic control. (a) Top-view SEM image of the microplate where the scale bar is 50 μm. The ICP-processed area is marked by the yellow dashed area. The width and thickness of the microplate are 39 μm and 561 nm, respectively. The lengths of covered and uncovered areas are 34 and 21 μm, respectively. (b) Laser spectra recorded from the covered and uncovered parts of lead halide perovskite microplate. The insets show the corresponding fluorescent microscope images.

around 532 nm, which is more than 20 nm smaller than the original part. This kind of wavelength shift is consistent with the results in Figure 3 and can also be explained by the changes of chemical composition in lead halide perovskite (see Figure 2c). It should be noted that the lasing behaviors observed in both original and ICP-processed parts are based on the WG mode lasing, which is formed in the transverse plane perpendicular to the substrate.9 In addition to the wavelength shift, another interesting point is that the lasing wavelengths of the covered part are well-maintained after the reaction in ICP. This shows that the PMMA layer can efficiently protect the lead halide perovskite and thus makes individual control of emission wavelengths on the same device possible. This kind of selective control on the same device can be a key step toward nanoscale control of lead halide perovskite devices. Given that PMMA photoresist could protect perovskite without degradation of optical properties, versatile and functional devices could be fabricated via standard semiconductor technology. This will open a new world for the perovskite material-based applications in optoelectronics and integrated photonics. From the results in Figures 2 and 3, we know that the absorption, PL, and laser emission can all be tuned by reaction time in ICP. The changes in PL and lasers can be applied to tune the color of light-emitting devices or lasers.27 Similarly, the changes in absorption band edge make the postsynthetic control of photodetector possible, especially the selective control of a single photodetector.28,29 Here, we note that the refractive index of lead halide perovskite can also be tuned. The absorption spectra in Figure 1a,d are not flat at longer wavelength. Such kinds of undulate spectra are caused by the interference between top and bottom surfaces of the single crystalline microplate. Consequently, the refractive index of perovskite can be simply obtained from these curves (Figure S11).30,31 The fitted results are shown in the Supporting Information. We can see that the refractive index is changed once the lead halide perovskite microplate is processed with ICP. Such kinds of changes are more dramatic near the absorption band edge. Taking the refractive index at 550 nm as an example, the maximal change is Δn = 0.2 after reaction in ICP for 60 s, which is large enough to tailor the resonant properties of photonic devices.32 In summary, we have studied the postsynthetic control of the optical properties of lead halide perovskite with standard semiconductor technology. By processing a CH3NH3PbBr3 microplate in ICP with chlorine, we find that the absorption,

Figure 4. Microlaser array with different lasing wavelengths. (a) Topview SEM image of the microwire array where the scale bar is 20 μm. (b) Laser spectrum of the microlaser array. The corresponding fluorescent microscope image is shown as an inset.

perovskite microwires are placed shoulder-to-shoulder via micromanipulation.8,9 Each microwire shows a single-mode laser emission at around 550 nm before reaction in ICP (Figure S8). Three perovskite microwires were individually processed in ICP for 0, 30, or 50 s. Then the three microwires were moved by a microfiber tip and placed side-by-side on a silicon grating. Figure 4b shows the laser spectrum of the microlaser array. We can see that the ICP-processed microwire laser array produces three laser groups, which come from three individual microwires. The detailed experimental results are presented in the Supporting Information. We note that the result in Figure 4 is only a simple demonstration experiment. The lasing wavelengths and the array numbers can be further improved by precisely controlling the reaction time and increasing the number of microwires. The most unique property of this postsynthetic control technique is that different locations on the same sample can be individually controlled, which is almost impossible in a conventional solution-processed technique. To illustrate this advantage, we have tailored another microplate with E-beam lithography and studied the corresponding lasing characteristics. The microplate was coated with 300 nm poly(methyl methacrylate) (PMMA) e-beam photoresist, and half was exposed by electron beam. After developing in (methyl isobutyl ketone) MIBK, half of the microplate was still coated with PMMA and the exposed half was exposed in air (see the SEM image of microplate in Figure 5a). Then the sample was placed into ICP and processed for 30 s (the details of fabrication can be found in Experimental Section). Figure 5b shows the laser spectra from different positions on the lead halide perovskite microplate. The PMMA-covered part generates laser peaks at around 554 nm, which is similar to all previously reported CH3NH3PbBr3 microlasers. The details in laser behavior can also be found in Figures S9 and S10. Once the exposed half was pumped, dramatic changes have been observed. While the fluorescent microscope image also shows two bright spots on the facets of microplate, the lasing wavelengths blue shift to 3889

DOI: 10.1021/acs.jpclett.6b01751 J. Phys. Chem. Lett. 2016, 7, 3886−3891

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of the platform was maintained at 5 °C; and the ICP power was 400 W. A 20−30 min condition test with the same recipe has been done to control the chamber environment. E-Beam Lithography. Basically, a 500 nm PMMA film is spincoated onto an ITO-coated glass with synthesized perovskite and baked at 40 °C for 1 h. Then the sample is exposed to the electron beam in E-beam writer (Raith E-line, 10 kV) and developed in the MIBK/isopropanol (IPA) (1:3) solution for 10 s. After being rinsed in IPA for 10 s, the sample is dried by a nitrogen gun and processed with ICP.

PL, and laser emission all shift to shorter wavelengths. Such kinds of wavelength shifts are found to be linearly dependent on the reaction time, and the total wavelength change can be as large as 50 nm. Our experimental results show that the ICP processing can be a nice technology to postsynthetically control the characteristics of microlasers or microdetectors. On the basis of this technique, a microlaser array that emits different lasing wavelengths has been demonstrated, and the local properties of a single lead halide perovskite microlaser have been selectively tuned. Compared with previous reports,21−23 the proposed method exhibits several advantages, such as facile patterning, high accuracy of both reaction postion and time, precise control of absorption and PL wavelength, morphology retention, and wide application range (microwires, microplates, and layers). In addition, the main device characteristics have been well-preserved during the reaction process for the first time. In addition, the postsynthetic control technique is not restricted in CH3NH3PbBr3. It might also be able to realize the alloys of CH3NH3PbClxI3−x and CH3NH3PbBrxI3−x via ion exchange in ICP and thus has the potential to tune the whole visible wavelength range. We believe that our postsynthetic control technique will shed light on the advances of lead halide perovskite based micro- and nano-sized optoelectronic or photonic devices.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpclett.6b01751. Experimental setups for measuring absorption and photoluminescence spectra, energy-dispersive X-ray spectroscopy and PL characteristics before and after chlorine gas processing, and ICP processing results of perovskite microstructures and simulation results (PDF)

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AUTHOR INFORMATION

Corresponding Authors

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*E-mail: [email protected]. *E-mail: [email protected].

EXPERIMENTAL SECTION Synthesis of CH3NH3PbBr3 Microwire. The CH3NH3PbBr3 perovskite microstructures were synthesized on a hydrophobic indium tin oxide (ITO) glass. Basically, 15 μL of 0.02 M CH3NH3Br·PbBr2 solution, which was prepared by mixing equal volumes of solutions of CH3NH3Br (0.04 M) and PbBr2 (0.04 M) in DMF (N,N-dimethylformamide), was cast onto an ITO glass. The ITO glass was amounted on four pieces of cleanroom wipers, which were immersed in 10 mL of CH2Cl2 in a 50 mL beaker. The beaker was sealed with two pieces of porous Parafilm (3M). After 24 h, CH3NH3PbBr3 perovskite microstructures can be obtained (Figure S12). Optical Characterization. The absorption of microwires and microplates is measured as the following. The white light was collimated and then focused by a 40× objective lens on the top surface of the sample. The transmitted light is collected by an optical lens and coupled to a spectrometer. The reflected light is collected by the same objective lens and detected by a chargecoupled device (CCD) camera and spectrometer (Figure S1). In the lasing experiment, the samples were mounted onto a three-dimensional translation stage under a homemade microscope and excited by a frequency-doubled laser (400 nm, using a BBO crystal) from a regenerative amplifier (repetition rate1 kHz, pulse width 100 fs, seeded by MaiTai, Spectra Physics). The pump light was focused on the top surface of the samples through a 40× objective lens, and the beam size was adjusted to ∼35 μm. The emitted light was collected by the same objective lens and coupled to a CCD (Princeton Instruments, PIXIS UV enhanced CCD) coupled spectrometer (Acton SpectroPro s2700) via a multimode fiber. The fluorescent microscope images were recorded by a CCD camera behind a long-pass filter. The experimental setup is shown in Figure S2. ICP Processing. The induced coupled plasma (ICP) processing was performed with Oxford instruments plasma technology 380 plasma source. Before the reaction, the chamber was pumped to the level of 10−9. During the ICP processing, the flow rate of the chlorine gas was 5 sccm; the chamber pressure was stabilized at 10 mTorr; the temperature

Author Contributions §

N.Z. and K.W. contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by National Nature Science Foundation of China under Grant NSFC-11374078 and Shenzhen fundamental research plan under Grants JCYJ20160301154309393, JCYJ20160505175637639, and JCYJ20160427183259083.

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REFERENCES

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DOI: 10.1021/acs.jpclett.6b01751 J. Phys. Chem. Lett. 2016, 7, 3886−3891

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DOI: 10.1021/acs.jpclett.6b01751 J. Phys. Chem. Lett. 2016, 7, 3886−3891