• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    One-pot synthesis of concentration and excitation dual-dependency truly full-color photoluminescence carbon dots

    2022-09-16 05:25:18ChenWeiShunHuFuxinLiangZhiningSongXueLiu
    Chinese Chemical Letters 2022年8期

    Chen Wei, Shun Hu, Fuxin Liang, Zhining Song,?, Xue Liu

    a Institute of Clean Energy Chemistry, Key Laboratory for Green Synthesis and Preparative Chemistry of Advanced Materials, College of Chemistry, Liaoning University, Shenyang 110036, China

    b Institute of Polymer Science and Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China

    ABSTRACT The paper describes a kind of truly full-color photoluminescence (PL) CDs.The CDs were prepared by using one-pot hydrothermally heating citric acid and formamide at 200 °C for 2 h.The CDs have three fluorescent centers at blue, green, and red light region.Their color was regulated through two means,including changing excitation wavelengths or CDs concentrations.The emission maxima changed from blue to red with the increase of excitation wavelengths or CDs concentrations.The full-color PL behavior of the CDs was inherited and conserved in the solid polymer matrix, giving multicolor CDs/polymer films and light emitting diodes (LEDs).White-light LED (WLED) with the CIE coordinate approaching to (0.31,0.32) were also achieved.

    Keywords:Carbon dots Full-color Fluorescent centers Concentration and excitation White-light LEDs

    Multicolor luminescent materials have received significant attention due to their broad application in sensing, bioimaging, fullcolor displays, light-emitting diodes, and optoelectronic devices[1–6].In these multicolor luminescent materials, rare-earth based nanoparticles, semiconductor quantum dots and organic fluorescent dyes have been developed [7–10].However, these luminescent materials often have many problems such as poor water solubility,complex preparation procedures, or high bio-toxicity [7–15].Moreover, current methods for regulating the colors of these materials are also limited.Therefore, it remains challenges to develop novel multicolor luminescent materials with high utility and rich color regulation.

    Carbon dots (CDs) as a novel type of multicolor luminescent materials have many remarkable advantages, such as superior optical properties, good solubility and biocompatibility, compared with traditional multicolor luminescent materials [16–20].The preparation procedures of CDs are simple and easy, and their raw materials are abundant [21,22].Hence, it is easier to prepare CDs with multicolor luminescence by choosing appropriate carbon source or controlling reaction conditions.A great variety of CDs with fullcolor emission (blue-red light region) have been successfully prepared by adjusting starting materials [23,24], reaction condition[25,26], or separation method (path-A) [27].Lin’s group synthesized three types of CDs inducing emissions in red, green and blue(RGB) three primary colors of luminescence through solvothermal treatment of three different phenylenediamine isomers as carbon sources [23].Sunet al.prepared multiple-color-emission CDs by regulating the thermal-pyrolysis temperature of citric acid and urea [26].Dinget al.reported that a kind of full-color light emitting CDs, which were hydrothermally synthesized in one pot and separatedviasilica column chromatography [27].Besides, some CDs can also achieve multicolor luminescence by changing the excitation wavelength [28,29], solvents [30,31], or CDs concentration [32,33] (path-B).Panet al.prepared excitation-dependent truly full-color CDs presenting unusually comparable emission intensity nearly across the entire range of visible spectrum [29].Wanget al.synthesized excitation-independent multicolor emissive CDs, which showed different color emissions in different solvents or polymer matrixes [30].Chenet al.reported concentrationdependent multicolor CDs with emissions changing from blue to orange light [33].Both these two methods (path-A and path-B)contribute significantly to the development of full-color CDs.Nevertheless, each of these methods has its own advantages and drawbacks.The full-color CDs from path-A (CDs-A) are generally able to access various color emissions with high intensity and efficiency.However, various colors of CDs-A are actually achieved from a group of CDs, and such kind of full-color CDs is suitable for fullcolor displays.On the other hand, the full-color CDs from path-B(CDs-B) can directly achieve various color emissions from a single CD.Such kind of full-color CDs is available for sensing through monitoring obvious stimuli-responsive color transition.Nevertheless, various colors of CDs-B are generally achieved from a fluorescent center, which results in low fluorescent intensity and efficiency of certain color emissions.Truly full-color CDs-B with multiple fluorescent centers at three primary colors were rarely reported.Truly full-color CDs can guarantee intensity and efficiency of various color emissions and have practical value.

    Fig.1.(a) TEM image the CDs; inset: HRTEM image and the particle size histograms of the CDs.(b) FT-IR spectra of the CDs.(c) XPS full-survey; (d) high-resolution C 1s; (e) high-resolution N 1s; (f) high-resolution O 1s XPS spectra of the CDs.

    Herein, we report a kind of concentration and excitation dual-dependency truly full-color fluorescent CDsviaa one-pot solvothermal synthesis by using citric acid and formamide (Scheme S1 in Supporting information).The CDs present full-color emission from blue to green, yellow, and red with the increase of excitation wavelength and its concentration.The full-color CDs are confirmed to contain multiple fluorescence emission centers in the 2D fluorescent excitation-emission matrix.They can be applied in preparing full-color polymer films and LEDs.

    The morphology and composition characterizations of the CDs including TEM, FT-IR and XPS were performed.The TEM image illustrates that the CDs are well-dispersed in ethanol (Fig.1a),with average particle sizes of approximately 2.9 nm.The highresolution TEM (HRTEM) image shows that the sample has similar well-resolved lattice fringes with a spacing of 0.21 nm, indicating the successful synthesis of well-crystallized CDs [34,35].The FTIR spectrum exhibits the characteristic absorption bands (Fig.1b),including the stretching vibrations of C=N/C=O, C=C and C–N at 1680, 1605, and 1390 cm?1, and the asymmetric and symmetric stretching vibrations of C–O–C at 1130 and 1075 cm?1.The broad absorption bands from 3200 cm?1to 3350 cm?1indicate the presence of amino (–NH2) and hydroxyl (–OH) functional groups on the surface of the CDs.Furthermore, the chemical compositions of the CDs were investigated by XPS analysis (Figs.1c-f), which further support the FT-IR analysis.For instance, the CDs mainly contain C, O, and N elements (i.e., C/O/N = 1.0/0.75/0.28, molar ratios).The typical high-resolution XPS C 1s spectrum can be deconvoluted into five binding energies (i.e., C–C/C=C, 284.4 eV; C–N, 285.5 eV;C–O, 286.5 eV; C=N/C=O, 287.8 eV; –COOH, 288.6 eV) (Fig.1d and Table S1 in Supporting information) [29,36].In the high-resolution XPS N 1s, two fitting peaks at 399.8 and 400.8 eV are corresponding to the graphitic-like/amino N and pyrrolic-like N, respectively(Fig.1e) [37].The two fitting peaks of O 1s XPS at 531.5 and 532.8 eV are attributed to C=O and C?O bonds (Fig.1f).These characterizations show the CDs compose of nano-scale graphitelike skeleton/core, and they are covered with N and O containing heterocyclic chemical structures and abundant amino and hydroxyl functional groups.

    Fig.2.(a) PL spectra of the CDs dispersed in ethanol solvent under different excitation wavelengths.(b) The maximum emissions under different excitation wavelengths and their corresponding normalized fluorescence intensity.(c) CIE chromaticity coordinate of blue, green, yellow, and red excited at the indicated wavelengths.(d) PL emission photographs of the CDs recorded under the excitation wavelengths from 370 nm to 600 nm.

    Fig.3.(a) UV–vis absorption spectra of the CDs prepared at 160, 180 and 200 °C,respectively; (b) Raman spectra of the CDs prepared at 160, 180 and 200 °C, respectively.

    Fig.4.(a) Photograph of the CDs ethanol solutions with various concentrations in daylight (upper) and 365 nm UV-light excitation (bottom).(b) CIE chromaticity coordinate of A1-A8 samples excited at the indicated wavelengths.The concentrations of A1-A8 samples are 0.0064, 0.0128, 0.0192, 0.032, 0.0448, 0.064, 0.128, and 0.192 mg/mL, respectively.(c) Normalized PL emission spectra of the A1 (Blue), A4(Green), A6 (Yellow), and A8 (Red) samples under their optimum excitation wavelength.

    The excitation-dependent optical properties of the CDs were thoroughly investigated by fluorescence (FL), UV–vis absorbance and Raman analysis.As shown in Fig.2a, there is no regular pattern in the variation of the fluorescence spectra of the CDs dispersed in ethanol solvent as altering the excitation wavelengths from 370 nm to 600 nm unlike most of the other CDs.The fluorescence emissions nearly cover the entire visible spectrum.The normalized maximum fluorescence intensities and their locations are provided in Fig.2b and Fig.S1a (Supporting information) for allowing easy observation.The emission wavelengths suffer a red-shift from 450 nm to 650 nm.Multiple platforms appear in the curve of the emission wavelength to excitation wavelength, demonstrating the CDs experience several fluorescence emitters.Under the combined effect of these emitters, all of these fluorescence spectra are asymmetric with a wide full width at half maximum (FWHM).From the curve of the fluorescence intensity to excitation wavelength, four peaks appear at 458, 536, 548, and 646 nm under the excitation wavelength of 380, 450, 470 and 590 nm, respectively.These four fluorescence spectra were converted to CIE coordinates to determine the exact spatial coordinates of the chromophores,and CIE color coordinates of blue (0.19, 0.21), green (0.34, 0.53),yellow (0.40, 0.55) and red (0.66, 0.31) emitters were achieved(Fig.2c).These colors are readily observed by naked eye as well from the photographed cuvettes (Fig.2d and Fig.S1b in Supporting information).The QYs of carbon dots under 380, 450, 470 and 590 nm are determined to be 11.1%, 21.3%, 15.9% and 9.4%, respectively.

    Fig.5.2D fluorescent matrix scan of the A1-A8 samples.

    Fig.6.(a) CDs/PVA films with multicolor emissions under the excitation of 365 nm UV-light; (b) blue-light, green-light, yellow light, and red-light LED prototypes.(c)WLED prototype and its solid-state emission spectrum.(d) CIE chromaticity coordinate of the WLED.

    The difference (ΔW) between the excitation wavelength and their maximum emission wavelength can reflect the degree of the excitation lights (Table S2 in Supporting information).The results show obvious variation in the corresponding differences among the various excitation lights, and again confirm the existence of multiple emitters.Moreover, it is obvious that the ΔWtend to converge when the emission wavelengths approach the optimum excitation wavelength of the corresponding emitters.This multicolor fluorescence phenomenon could be formed by the sp2carbon-induced variation in energy gaps between theπandπ?states [38,39].The size of the sp2carbon domains can determine the quantum confinement effect of the CDs and drive their emission toward the light region with long emissions [3].To elucidate the relationship between the sp2structure of the CDs and their luminescent behavior, several CDs were prepared with the same starting materials of equal amounts under different hydrothermal temperatures (Fig.S2 in Supporting information).The fluorescence emitters at three primary colors (red, green, and blue light) were compared at various preparation temperatures.The CDs at 160 and 180 °C show two main fluorescence emitters in the blue light and green light region; the CDs at 220 °C show three fluorescence emitters in the three primary color region similar to the above-mentioned CDs at 200 °C; the CDs at 240 °C show only one fluorescence emitter in the blue light region.Over-carbonization has occurred in the CDs at 240 °C, and makes them show monochromatic luminescence.The fluorescence emitter in the blue region appears in all of the CDs, and is hardly affected by their preparation temperatures.The fluorescence emitter in the green light region is underpowered by the high temperature.Conversely, the fluorescence emitter in the red light region is enhanced with the increasing preparation temperatures.The characteristic absorption in the UV–vis spectra can reflect the structural features of the CDs, including sp2structure(Fig.3a and Fig.S3 in Supporting information).In the UV region of 210–350 nm, a single peak is observed at 345 nm with a shoulder peak at 282 nm, corresponding to then-π?transition of the C=O bond and theπ-π?transition of the C=N bonds, respectively.With the increased preparation temperatures, then-π?peak is reduced while theπ-π?peak is elevated.The elevatedπ-π?transition suggests an increased energy gap between theπandπ?states and an increased conjugated sp2domain [40].Besides, the elevated visible absorption at 560 nm in the UV–vis spectra can also confirm the size increase of the conjugated sp2domain in the particles [23].Fig.3b shows the Raman spectra of three CDs at 160, 180 and 200 °C.The peaks at 1387 and 1525 cm?1in the Raman spectra correspond to the disordered (D band) and graphite (G band) carbon in carbon materials [26,39].The ratio ofID/IGis 1.12, 1.09 and 1.06 at 160, 180 and 200 °C, respectively.The decreasedID/IGalso implies the increased number of embedded graphitic carbon atoms in the CDs with their increased preparation temperatures, that is,the increased conjugated sp2domain in the CDs.

    The CDs present not only excitation-dependent luminescence,but also concentration-dependent luminescence.In order to investigate the concentration-dependent PL behavior of the CDs, we prepared a series of CDs ethanol solutions with the concentration of 0.0064, 0.0128, 0.0192, 0.032, 0.0448, 0.064, 0.128 and 0.192 mg/mL, respectively (A1-A8 samples).With the increased concentration of the CDs, the colors of CDs solutions gradually deepen in daylight (Fig.4a, upper).Interestingly, under the excitation of 365 nm UV-light, the CDs solutions display full-color PL emission, which can be directly observed by naked eye as well(Fig.4a, bottom).The increase in the CDs concentration leads to a red shift in their emission.Furthermore, the normalized PL emission spectra of the A1-A8 samples were recorded under the excitation wavelength of 400 nm (Fig.S4 in Supporting information), and the PL emission centers of the CDs exhibit gradual bathochromic shift with the increase of the CDs concentration.The fluorescence spectra were converted to CIE coordinates to determine the exact spatial coordinates of these CDs.Commission Internationale de L’Eclairage 1931 (CIE) coordinate of A1-A8 samples shows that the CDs excited at 400 nm can achieve full-color emission from blue to red (Fig.4b).The corresponding CIE coordinates are (0.16, 0.19),(0.21, 0.32), (0.25, 0.44), (0.35, 0.57), (0.44, 0.54), (0.52, 0.47), (0.61,0.38), and (0.67, 0.32), respectively.Four CDs samples (A1, A4, A6,and A8), their CIE color coordinates of blue, green, yellow, and red, were chosen to further investigate their PL properties in details.Under the optimum excitation wavelengths (λoe), their maximum fluorescence emissions (λme) are just located in the blue light (λoe= 380 nm,λme= 446 nm), green light (λoe= 450 nm,λme= 529 nm), yellow light (λoe= 470 nm,λme= 547 nm),and red light (λoe= 590 nm,λme= 653 nm) region, respectively (Fig.4c).Their PL spectra under different excitation wavelengths and corresponding excitation-emission spectra under theλoeare shown in Figs.S5 and S6 (Supporting information).The CDs at lower concentrations (A1, A4 and A6) show three main fluorescence emitters in the blue light, green light, and red light region, and A8 sample show two main fluorescence emitters in the green light and red light region.With the raise of the concentration, the fluorescence emitters in the blue light region are gradually underpowered; those in the green light region increase first and then decrease; those in the red light region remain upregulated.The UV–vis absorption spectra (Fig.S7 in Supporting information) of the CDs can illustrate the full-color fluorescence emissive phenomenon.The CDs with the emissions in the longwavelength region have an obvious absorption peak in long wavelength, which may be attributable to the formation of large sp2conjugation [23,35].With the increasing CDs concentration, the UV–vis absorption of the CDs in the long-wavelength region increases significantly.

    To further investigate the mechanism of the concentrationdependent PL behavior of the CDs, specified 2D fluorescent matrix scans were performed on the A1-A8 CDs.The fluorescence center in the blue light region lies within the excitation wavelength range from 360 nm to 390 nm (Fig.5a).A new fluorescent center appears in the green light region in A2 CDs (Fig.5b).Clearly, the fluorescence center in the blue light and green light region are located at 447 and 515 nm, with the excitation wavelength of 375 and 415 nm, respectively.With the increase of CDs concentration (A1-A3), the emission intensity of the green fluorescent center gradually increases.The emission intensity is raised with the red shift of the emission wavelength (A4-A6), implying an effective energy transfer from blue light to green light regionviaa broad band absorption, which can be inferred from the UV–vis absorption spectra of the CDs in Fig.S7 (Supporting information).A further increase in CDs concentration causes the disappearance of the fluorescent emissive center in blue light region (A7).Next, the fluorescence emission center gradually shifts towards the red light region.A large irregular emission area in the red light region is observed in A8, showing a new fluorescent emissive center at 650 nm.The fluorescence center in the red light region can be assigned to the intrinsic energy level of the N-related defect states between surface bands [1].

    It has been reported that the full-color PL behavior of the CDs can be extended to solid-state films for solid-state lighting.In this case, full-color emissive CDs/polyvinyl alcohol (PVA) composite films were successfully fabricated (Fig.6a).PVA matrix favors the CDs with different concentrations to maintain their fullcolor PL behavior when the films are shaped [40].Notably, the obtained CDs/PVA films inherit the concentration and excitation dualdependency full-color PL behavior.With increased CDs concentrations, CDs/PVA films emit a strong light from blue to red under UV light of 365 nm.The normalized solid-state PL emission spectra of the CDs/PVA films show obvious red-shift from blue light region to red light region with the increased excitation wavelength(Fig.S8a in Supporting information).The corresponding CIE coordinates of the CDs/PVA composite films at different excitation wavelengths are (0.26, 0.35), (0.32, 0.50), (0.41, 0.52), and (0.54, 0.45),respectively (Fig.S8b in Supporting information).CDs-based LEDs with various color emissions were prepared by using the corresponding CDs/PVA films and InGaN LED chips centered at 365 nm.These LEDs emit bright blue light, green light, yellow light, and red light (Fig.6b and Fig.S9 in Supporting information).Furthermore,by combining blue light and yellow light CDs/PVA films, WLED with the CIE coordinate approaching to (0.31, 0.32) were achieved(Figs.6c and d), realizing the LEDs with full-wavelength emissions.In a word, the full-color CDs have proved promising and very useful in manufacturing forward-looking multicolor films and LEDs.

    In summary, both concentration and excitation doubledependence fluorescent CDs with truly full-color emission have been synthesized through a simple one-pot hydrothermal method.The CDs with tunable fluorescence colors can achieve full-color PL emission (including three primary color emissions) by adjusting the excitation wavelength and concentration.The excitation and concentration double-dependence PL behavior of the CDs can be attributed to the multiple emission centers formed from the different-sized conjugated sp2domains of the CDs.It can be confirmed that there are three fluorescent centers in the CDs corresponding to blue, green, and red light region in the 2D fluorescent excitation-emission matrix.Based on the unique multicolor PL properties, the CDs/PVA films were prepared and show similar excitation and concentration double-dependence solid-state PL behavior.Meanwhile, LEDs and WLED based on the CDs/PVA films were also fabricated for multicolor lighting.These applications confirm the versatile functions and bright prospect of the CDs in multicolor prototypes.

    Declaration of competing interest

    The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

    Acknowledgments

    This work was supported by National Natural Science Foundation of China (No.51873085) and Liaoning Revitalization Talents Program (No.XLYC2007056).

    Supplementary materials

    Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2022.01.053.

    国产爱豆传媒在线观看 | 成人三级黄色视频| 19禁男女啪啪无遮挡网站| 又大又爽又粗| 欧美中文综合在线视频| 国语自产精品视频在线第100页| 一进一出抽搐gif免费好疼| 久久99热这里只有精品18| 满18在线观看网站| 精品久久久久久成人av| 欧美日韩精品网址| 精品国产一区二区三区四区第35| 男女之事视频高清在线观看| 欧美一级毛片孕妇| 欧美绝顶高潮抽搐喷水| 精品国产一区二区三区四区第35| 男女之事视频高清在线观看| 午夜成年电影在线免费观看| 少妇熟女aⅴ在线视频| 亚洲 国产 在线| 波多野结衣高清作品| 日韩高清综合在线| 精品国产乱子伦一区二区三区| 亚洲五月色婷婷综合| 久久狼人影院| 在线观看午夜福利视频| 国产精品一区二区免费欧美| 精品一区二区三区视频在线观看免费| 国产91精品成人一区二区三区| 啪啪无遮挡十八禁网站| 国产人伦9x9x在线观看| 婷婷精品国产亚洲av| 精品国产一区二区三区四区第35| 老鸭窝网址在线观看| 成人三级做爰电影| 欧美性长视频在线观看| 日本 av在线| 国产成人精品久久二区二区91| 国产亚洲欧美98| 91在线观看av| 在线视频色国产色| 免费人成视频x8x8入口观看| 高清在线国产一区| 亚洲三区欧美一区| 国产欧美日韩精品亚洲av| 给我免费播放毛片高清在线观看| 高潮久久久久久久久久久不卡| 亚洲三区欧美一区| 久久香蕉国产精品| 在线观看日韩欧美| 久久精品国产综合久久久| 成人av一区二区三区在线看| 国产欧美日韩精品亚洲av| 麻豆国产av国片精品| 国产成人av激情在线播放| 黄网站色视频无遮挡免费观看| 欧美黑人精品巨大| 国产亚洲av嫩草精品影院| 91老司机精品| 男人舔女人的私密视频| 久久人妻福利社区极品人妻图片| 99久久综合精品五月天人人| 亚洲精品一卡2卡三卡4卡5卡| 在线观看一区二区三区| 18美女黄网站色大片免费观看| www.熟女人妻精品国产| 黄色 视频免费看| 中文字幕人妻丝袜一区二区| 国产麻豆成人av免费视频| 日日爽夜夜爽网站| 午夜福利高清视频| 亚洲性夜色夜夜综合| 久久久精品国产亚洲av高清涩受| 中文字幕高清在线视频| 久久婷婷成人综合色麻豆| 久久久久久九九精品二区国产 | 色哟哟哟哟哟哟| 午夜福利一区二区在线看| 两个人视频免费观看高清| 国产亚洲欧美98| 看片在线看免费视频| 成人18禁高潮啪啪吃奶动态图| av片东京热男人的天堂| 中国美女看黄片| 午夜福利视频1000在线观看| 免费在线观看成人毛片| 日韩欧美国产在线观看| 亚洲专区字幕在线| 亚洲国产高清在线一区二区三 | 免费看美女性在线毛片视频| 中亚洲国语对白在线视频| 欧美人与性动交α欧美精品济南到| 大香蕉久久成人网| 精品一区二区三区四区五区乱码| 国产人伦9x9x在线观看| 欧美激情久久久久久爽电影| 欧美不卡视频在线免费观看 | 成人国产综合亚洲| 精品不卡国产一区二区三区| 午夜福利高清视频| 国产私拍福利视频在线观看| 一级片免费观看大全| 精品熟女少妇八av免费久了| 国产精品电影一区二区三区| 亚洲三区欧美一区| 免费在线观看完整版高清| 69av精品久久久久久| 亚洲成人久久爱视频| 国产激情欧美一区二区| 免费在线观看影片大全网站| 97碰自拍视频| 国产精品日韩av在线免费观看| 欧美激情极品国产一区二区三区| 久久午夜亚洲精品久久| 淫妇啪啪啪对白视频| 999久久久精品免费观看国产| 在线免费观看的www视频| 日本 欧美在线| 日韩欧美在线二视频| 在线观看舔阴道视频| 婷婷精品国产亚洲av| 超碰成人久久| 国产精品亚洲一级av第二区| 久久久久久久久久黄片| 三级毛片av免费| 国产免费男女视频| 久久亚洲精品不卡| 后天国语完整版免费观看| 首页视频小说图片口味搜索| 成人国产综合亚洲| 国产av一区二区精品久久| 欧美日韩亚洲综合一区二区三区_| 久久久国产成人精品二区| 成人国产综合亚洲| av有码第一页| 午夜成年电影在线免费观看| www.自偷自拍.com| 欧美成人一区二区免费高清观看 | 成年女人毛片免费观看观看9| 成年版毛片免费区| 亚洲精品粉嫩美女一区| 国产成人啪精品午夜网站| 久久久久久免费高清国产稀缺| 天堂√8在线中文| aaaaa片日本免费| 日韩精品中文字幕看吧| 国产私拍福利视频在线观看| 欧美黄色淫秽网站| 亚洲五月色婷婷综合| 在线天堂中文资源库| 好男人在线观看高清免费视频 | 一级片免费观看大全| 我的亚洲天堂| 精品国产一区二区三区四区第35| 一级作爱视频免费观看| 国语自产精品视频在线第100页| 日本精品一区二区三区蜜桃| www国产在线视频色| 侵犯人妻中文字幕一二三四区| 亚洲男人天堂网一区| 人人妻人人澡人人看| 欧美性长视频在线观看| 亚洲精品粉嫩美女一区| www.熟女人妻精品国产| 国产野战对白在线观看| 亚洲五月婷婷丁香| 国产免费男女视频| 亚洲精品国产精品久久久不卡| 女人被狂操c到高潮| 侵犯人妻中文字幕一二三四区| 老汉色av国产亚洲站长工具| 国产激情久久老熟女| 久久久久久免费高清国产稀缺| 国产精品爽爽va在线观看网站 | 97碰自拍视频| 99riav亚洲国产免费| 久久久久久久久中文| 日韩 欧美 亚洲 中文字幕| 亚洲成av人片免费观看| 久久久久国产精品人妻aⅴ院| 欧美黄色片欧美黄色片| e午夜精品久久久久久久| 亚洲午夜精品一区,二区,三区| 88av欧美| 国产激情久久老熟女| 日韩欧美 国产精品| 日韩欧美免费精品| 中文字幕久久专区| 国产午夜福利久久久久久| 国产一区二区三区视频了| 国产97色在线日韩免费| 美国免费a级毛片| 久久国产乱子伦精品免费另类| 变态另类丝袜制服| 精品欧美国产一区二区三| 真人做人爱边吃奶动态| 成人av一区二区三区在线看| 久久久久久久久久黄片| 国产av又大| 两个人看的免费小视频| 久久精品91蜜桃| 日本精品一区二区三区蜜桃| 欧美日韩福利视频一区二区| 制服人妻中文乱码| 亚洲精品一卡2卡三卡4卡5卡| 97人妻精品一区二区三区麻豆 | 午夜久久久久精精品| 亚洲精品在线观看二区| 1024手机看黄色片| 777久久人妻少妇嫩草av网站| 99在线人妻在线中文字幕| 国产精品久久久久久人妻精品电影| 级片在线观看| 18禁黄网站禁片免费观看直播| 久久九九热精品免费| 国产伦在线观看视频一区| 免费在线观看完整版高清| 女人被狂操c到高潮| 妹子高潮喷水视频| 久久精品成人免费网站| 欧美国产精品va在线观看不卡| 日韩欧美三级三区| 国产激情久久老熟女| 嫩草影视91久久| 国产精品久久视频播放| 国产亚洲精品一区二区www| 岛国视频午夜一区免费看| 国产日本99.免费观看| 在线观看66精品国产| 欧美日韩中文字幕国产精品一区二区三区| 中文在线观看免费www的网站 | 亚洲狠狠婷婷综合久久图片| 精品一区二区三区av网在线观看| 久久精品夜夜夜夜夜久久蜜豆 | 老司机午夜福利在线观看视频| 久久香蕉精品热| 国产伦人伦偷精品视频| 久久久久久久久中文| 久久精品aⅴ一区二区三区四区| 中文字幕人妻熟女乱码| 在线观看www视频免费| 精品免费久久久久久久清纯| 在线观看舔阴道视频| 国产成年人精品一区二区| 狂野欧美激情性xxxx| 悠悠久久av| av超薄肉色丝袜交足视频| 中文资源天堂在线| 国产一区二区激情短视频| 级片在线观看| 国产又爽黄色视频| 人人妻人人澡人人看| 国产亚洲精品久久久久久毛片| 久久中文字幕人妻熟女| 色播在线永久视频| 哪里可以看免费的av片| 最近最新中文字幕大全电影3 | 午夜激情福利司机影院| 亚洲成人久久性| 免费搜索国产男女视频| www日本在线高清视频| 久久久国产精品麻豆| 国产精品一区二区免费欧美| 香蕉av资源在线| 欧美一级毛片孕妇| 无遮挡黄片免费观看| 欧美人与性动交α欧美精品济南到| 精品福利观看| 成人午夜高清在线视频 | av视频在线观看入口| 人人妻人人看人人澡| 亚洲,欧美精品.| 亚洲成国产人片在线观看| ponron亚洲| 18禁裸乳无遮挡免费网站照片 | 美女高潮到喷水免费观看| 一本精品99久久精品77| 在线永久观看黄色视频| 狂野欧美激情性xxxx| 97碰自拍视频| 99久久国产精品久久久| 日本免费一区二区三区高清不卡| 91国产中文字幕| 欧美激情久久久久久爽电影| 免费观看人在逋| 免费在线观看日本一区| 国产91精品成人一区二区三区| 亚洲欧美精品综合久久99| 成人国产一区最新在线观看| 一级作爱视频免费观看| 99久久久亚洲精品蜜臀av| 精品久久久久久久末码| 国产乱人伦免费视频| 中文字幕另类日韩欧美亚洲嫩草| 亚洲国产日韩欧美精品在线观看 | 好看av亚洲va欧美ⅴa在| 黄色视频不卡| 看免费av毛片| 哪里可以看免费的av片| 久久青草综合色| 国产一卡二卡三卡精品| 级片在线观看| 国产91精品成人一区二区三区| 色av中文字幕| 精品国产一区二区三区四区第35| 中出人妻视频一区二区| 国产一级毛片七仙女欲春2 | 亚洲中文av在线| 国产一区二区在线av高清观看| 中国美女看黄片| 国产高清videossex| 香蕉久久夜色| 久久人人精品亚洲av| 亚洲七黄色美女视频| 午夜久久久久精精品| 欧美一区二区精品小视频在线| 精品国产乱码久久久久久男人| 日韩欧美在线二视频| 日韩欧美 国产精品| 日日干狠狠操夜夜爽| 国产aⅴ精品一区二区三区波| 12—13女人毛片做爰片一| 日本免费a在线| 在线播放国产精品三级| 悠悠久久av| 亚洲欧美一区二区三区黑人| 国产aⅴ精品一区二区三区波| 好男人电影高清在线观看| 欧美日韩乱码在线| 精品国产乱子伦一区二区三区| 最好的美女福利视频网| 黄片大片在线免费观看| 免费一级毛片在线播放高清视频| 亚洲,欧美精品.| 国产人伦9x9x在线观看| 亚洲第一青青草原| 黄色a级毛片大全视频| 亚洲成人国产一区在线观看| 亚洲人成网站高清观看| 老汉色av国产亚洲站长工具| √禁漫天堂资源中文www| 午夜福利高清视频| 国产精品自产拍在线观看55亚洲| xxxwww97欧美| 亚洲精品一卡2卡三卡4卡5卡| 日韩欧美一区视频在线观看| 高清毛片免费观看视频网站| 变态另类成人亚洲欧美熟女| 午夜免费激情av| 亚洲熟女毛片儿| 亚洲五月天丁香| 国语自产精品视频在线第100页| 欧美成人性av电影在线观看| 亚洲国产精品合色在线| 母亲3免费完整高清在线观看| 99国产精品一区二区三区| 午夜亚洲福利在线播放| 色老头精品视频在线观看| 最近最新中文字幕大全免费视频| 美女国产高潮福利片在线看| 老鸭窝网址在线观看| 国产黄片美女视频| 欧美成人一区二区免费高清观看 | 一本精品99久久精品77| 欧美黑人欧美精品刺激| 怎么达到女性高潮| 女性生殖器流出的白浆| 亚洲av成人一区二区三| 中文字幕另类日韩欧美亚洲嫩草| 免费在线观看视频国产中文字幕亚洲| 亚洲九九香蕉| 国产精品乱码一区二三区的特点| 亚洲国产精品成人综合色| 欧美日韩瑟瑟在线播放| 在线免费观看的www视频| 最近最新中文字幕大全电影3 | 精品午夜福利视频在线观看一区| 美女免费视频网站| √禁漫天堂资源中文www| 国产av一区二区精品久久| 亚洲第一电影网av| 亚洲精品色激情综合| 久久热在线av| 变态另类丝袜制服| 91在线观看av| 两个人视频免费观看高清| 国产精品国产高清国产av| 亚洲一码二码三码区别大吗| 欧美精品亚洲一区二区| 日韩大码丰满熟妇| 精品少妇一区二区三区视频日本电影| 久久久久九九精品影院| 每晚都被弄得嗷嗷叫到高潮| 精品一区二区三区四区五区乱码| 日韩成人在线观看一区二区三区| 熟女少妇亚洲综合色aaa.| 日韩精品免费视频一区二区三区| 国产av一区在线观看免费| 午夜免费观看网址| 国产99久久九九免费精品| 欧美激情极品国产一区二区三区| 亚洲av成人一区二区三| 亚洲七黄色美女视频| 亚洲色图av天堂| 久久久久国内视频| 国产一区二区三区视频了| 亚洲色图 男人天堂 中文字幕| 国产午夜福利久久久久久| 欧美人与性动交α欧美精品济南到| 日韩欧美 国产精品| 国产成人一区二区三区免费视频网站| 91字幕亚洲| e午夜精品久久久久久久| 国产成人系列免费观看| 亚洲国产中文字幕在线视频| 欧美黄色片欧美黄色片| 成人精品一区二区免费| 日本免费a在线| 老熟妇乱子伦视频在线观看| 这个男人来自地球电影免费观看| 999精品在线视频| 一进一出抽搐动态| 色在线成人网| 亚洲第一电影网av| 久久精品影院6| 亚洲中文日韩欧美视频| 精品国产乱码久久久久久男人| 不卡av一区二区三区| 欧美在线一区亚洲| 国产午夜福利久久久久久| 久99久视频精品免费| 精品人妻1区二区| 国产成人欧美在线观看| 亚洲精品久久成人aⅴ小说| 国产aⅴ精品一区二区三区波| 亚洲国产欧洲综合997久久, | 两个人视频免费观看高清| 手机成人av网站| 99riav亚洲国产免费| 黄色 视频免费看| 亚洲人成伊人成综合网2020| 亚洲国产看品久久| 国产精品一区二区免费欧美| 一个人免费在线观看的高清视频| 岛国在线观看网站| 久久性视频一级片| 一级毛片精品| 国产又爽黄色视频| 男人操女人黄网站| 国产精品一区二区精品视频观看| 国产av不卡久久| svipshipincom国产片| 亚洲国产精品999在线| 久久久精品国产亚洲av高清涩受| 久久精品91蜜桃| www.www免费av| 国产精品一区二区精品视频观看| 91av网站免费观看| 中文字幕高清在线视频| 在线天堂中文资源库| 午夜免费鲁丝| 日韩欧美三级三区| 国产精品久久电影中文字幕| 亚洲国产精品sss在线观看| 欧美色欧美亚洲另类二区| 日本免费一区二区三区高清不卡| a在线观看视频网站| 久热爱精品视频在线9| 国产精品自产拍在线观看55亚洲| 99精品在免费线老司机午夜| 国产欧美日韩精品亚洲av| 亚洲人成网站高清观看| 国产91精品成人一区二区三区| 脱女人内裤的视频| 男女之事视频高清在线观看| 一级黄色大片毛片| 在线观看日韩欧美| 精华霜和精华液先用哪个| 久久久久精品国产欧美久久久| 亚洲成av片中文字幕在线观看| 人妻丰满熟妇av一区二区三区| 国产黄a三级三级三级人| 在线观看舔阴道视频| 男女视频在线观看网站免费 | 男女下面进入的视频免费午夜 | 久久精品夜夜夜夜夜久久蜜豆 | 亚洲欧美精品综合久久99| 变态另类成人亚洲欧美熟女| 亚洲狠狠婷婷综合久久图片| 一级毛片精品| 88av欧美| 丰满人妻熟妇乱又伦精品不卡| 波多野结衣av一区二区av| 久久这里只有精品19| 精品电影一区二区在线| 久久久国产成人免费| 亚洲精品国产区一区二| 欧美乱妇无乱码| 日韩中文字幕欧美一区二区| 丝袜人妻中文字幕| 少妇 在线观看| 免费看十八禁软件| 激情在线观看视频在线高清| 最近最新中文字幕大全免费视频| 无限看片的www在线观看| 一个人免费在线观看的高清视频| 国产激情欧美一区二区| АⅤ资源中文在线天堂| 国产人伦9x9x在线观看| 久久精品国产清高在天天线| 高清在线国产一区| 国产av一区二区精品久久| www.精华液| 男女床上黄色一级片免费看| 一本大道久久a久久精品| 久久久久九九精品影院| 男女午夜视频在线观看| 成人18禁高潮啪啪吃奶动态图| videosex国产| 国产精品免费视频内射| 99热6这里只有精品| 男女下面进入的视频免费午夜 | 午夜a级毛片| 丁香六月欧美| av视频在线观看入口| 久久久久久免费高清国产稀缺| x7x7x7水蜜桃| 国产91精品成人一区二区三区| 色播在线永久视频| 午夜福利在线观看吧| 日韩精品青青久久久久久| 欧美国产日韩亚洲一区| 国产午夜精品久久久久久| 美女国产高潮福利片在线看| 可以在线观看的亚洲视频| 久久精品夜夜夜夜夜久久蜜豆 | 亚洲欧美日韩高清在线视频| 久久精品国产亚洲av高清一级| 国产视频一区二区在线看| 久久久精品国产亚洲av高清涩受| 久久精品国产亚洲av香蕉五月| 波多野结衣巨乳人妻| 久久天躁狠狠躁夜夜2o2o| 欧美又色又爽又黄视频| 丰满人妻熟妇乱又伦精品不卡| 视频区欧美日本亚洲| 亚洲一区中文字幕在线| 别揉我奶头~嗯~啊~动态视频| 97人妻精品一区二区三区麻豆 | 亚洲精品在线观看二区| 国产aⅴ精品一区二区三区波| 俄罗斯特黄特色一大片| 国产99白浆流出| 精品午夜福利视频在线观看一区| 哪里可以看免费的av片| 亚洲色图av天堂| 午夜激情福利司机影院| 亚洲成人国产一区在线观看| 欧美乱色亚洲激情| 后天国语完整版免费观看| 啦啦啦免费观看视频1| 日日爽夜夜爽网站| 久久天躁狠狠躁夜夜2o2o| 国产av在哪里看| 国产精品一区二区免费欧美| 两个人视频免费观看高清| 精品电影一区二区在线| 黄色丝袜av网址大全| av超薄肉色丝袜交足视频| 日韩欧美国产一区二区入口| 级片在线观看| 午夜亚洲福利在线播放| 一区二区三区高清视频在线| 99热这里只有精品一区 | 国产精品影院久久| 九色国产91popny在线| 亚洲精品中文字幕一二三四区| 日韩欧美 国产精品| 成人18禁在线播放| 亚洲九九香蕉| 免费在线观看影片大全网站| 日韩欧美在线二视频| 听说在线观看完整版免费高清| 一区二区三区激情视频| 精品日产1卡2卡| 成人亚洲精品一区在线观看| 日韩中文字幕欧美一区二区| 精品日产1卡2卡| 90打野战视频偷拍视频| 动漫黄色视频在线观看| 欧美另类亚洲清纯唯美| 嫩草影院精品99| 亚洲一区二区三区色噜噜| 亚洲男人的天堂狠狠| 国产精品自产拍在线观看55亚洲| 精品一区二区三区视频在线观看免费| 日韩一卡2卡3卡4卡2021年| 中文字幕人妻丝袜一区二区| 国产乱人伦免费视频| 国产亚洲欧美98| 在线天堂中文资源库| 亚洲五月色婷婷综合| 久久久久国产一级毛片高清牌| 波多野结衣高清作品| 婷婷精品国产亚洲av| 国产精品亚洲av一区麻豆| 女生性感内裤真人,穿戴方法视频| 精品少妇一区二区三区视频日本电影| 国产区一区二久久| 在线天堂中文资源库| 欧美成人午夜精品| 成人三级做爰电影| 亚洲狠狠婷婷综合久久图片| 久久婷婷成人综合色麻豆| 在线播放国产精品三级|