Research progress on nonlinear optics of polyvinylidene fluorid and its copolymers films
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摘要:
聚偏二氟乙烯(PVDF)及其共聚物薄膜拥有极佳的电活性、较高的衍射效率、显著的非线性光学效应,广泛应用于光电转换、光调控、光开关等光电功能器件等。本文简要介绍了近年来PVDF及其共聚物薄膜非线性光学研究方面的主要进展,指出该类薄膜共混、纳米掺杂、超薄化的发展方向。同时指出需从第一性原理-光子带隙计算着手研究其非线性光学性质,以高灵敏度Z-扫描及马克条纹法结合椭偏为主要测量方式。本综述将为该类薄膜的非线性光学研究及制备提供一定的参考。
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关键词:
- 聚偏二氟乙烯及其共聚物 /
- 薄膜 /
- 铁电 /
- 非线性光学
Abstract:Polyvinylidene fluoride (PVDF) and its copolymers films have been extensively used in photoelectric functional devices such as photoelectric conversion, optical regulation, optical switch. They are the most important polymeric ferroelectricity materials with excellent electro-active properties, high diffraction efficiency and significant nonlinear optical effect. We summarize the progress in nonlinear optical effect of polyvinylidene fluoride and its copolymers films both in domestic and foreign research within the last several years. We illustrate that the development direction of the films will be nanoscale-doping, blending modification and ultrathin. The nonlinear optical properties should be investigated by the first-principle and photonic band gap calculations, and measured by the means of the high sensitivity Z-scan, Marker fringe combing with ellipsometry. This study can provide an insight for the development and utilization for polyvinylidene fluoride and its copolymers films in future.
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图 1 Z-扫描技术示意图。(a)Z-扫描技术原理:Ⅰ表示高斯光进入非线性材料后的波前畸变,Ⅱ为Z-扫描实验装置,其中D1与D2为光电探测器,D2/D1比值与Z存在函数关系[20];(b)通过马克条纹技术测量二阶及三阶非线性参数示意[21];(c)质心扫描技术原理[24]
Figure 1. Schematic illustration of the Z-scan technique. (a) The principle of the Z-scan technique: Ⅰ-the wavefront deformation of Gaussian beam when entering nonlinear materials, Ⅱ-the Z-scan experimental apparatus in which the ratio D2/D1 is recorded as a function of the sample position Z, D1 and D2 are photodetectors[20]; (b) setup for second and third harmonic generation by means of the Maker fringe technique[21]; (c) the principle of barycentric scan technique[24]
图 3 PVDF及其共聚物光学薄膜非线性光学经典研究示意图。(a)用于二次谐波测试的PVDF 楔形薄膜的几何形状, k表示入射激光传输方向[4];(b)PVDF的LB膜红外-椭偏谱中测得的消光系数k||、k┴ 与折射率n||、n┴[57];(c)通过绕垂直轴旋转平面样品获得的马克条纹,入射光为水平偏振光。上图:当入射偏振光垂直于丁香酚溶液,在67.8°入射角下的相位匹配证据,二次谐波仍为水平方向;下图:在注满丁香酚溶液的透明试管中,通过绕垂直轴旋转极化共聚物膜获得的马克条纹,入射偏振光和二次谐波均为水平方向[52];(d) 当楔形样品在平行于激光束方向上平移时获得的SHG振荡条纹图[4]
Figure 3. Schematic illustration of classical research on nonlinear optics of PVDF and its copolymer optical thin films. (a) Sample geometry and orientation for SHG measurements on PVDF film. The direction of the laser beam propagation corresponds to k[4]. (b) The attenuation constants k|| and k┴ and the refractive indices n|| and n┴ of the LB films obtained from the IR-VASE (Variable angle spectrometer ellipsometry) data analysis[57]. (c) Maker fringes obtained by rotating the planar samples around a vertical axis, with a horizontal polarization of the incident beam. Above: evidence of phase matching at an incidence angle of 67.8° in Eugenol when the incident polarization is vertical. The SHG polarization is still horizontal. Below: Maker fringes obtained by rotating the poled copolymer film around a vertical axis in a transparent cell filled with Eugenol. The incident polarization and the SHG polarization are horizontal[52]. (d) SHG fringes pattern obtained when wedge sample is translated parallel to its length across laser beam (fundamental)[4]
图 4 PVDF/金属氧化物纳米复合薄膜的非线性光学性能。(a)PMMA/PVDF-ZnO纳米聚合物薄膜的透射率变化[78];(b)PVDF/ZnO/CuO 纳米聚合物薄膜线性吸收系数谱[81] ;(c)单一PVDF及PVDF-ZnO纳米薄膜的直接带隙[73]; (d)PVDF/ZnO纳米复合薄膜在开孔Z-扫描模式下的归一化透射率与样品位置的关系[74]
Figure 4. NLO properties of PVDF/metallic oxide nanocomposites films. (a) The transmittance of PMMA/PVDF-ZnO nanocomposites[78]; (b) linear absorption coefficient spectra of PVDF/ZnO/CuO nanocomposites[81]; (c) plots (direct band gap) for PVDF pristine and PVDF-ZnO Nanocomposites[73]; (d) the normalized transmittance as a function of sample position in open-aperture Z-scan for PVDF/ZnO nanocomposites [74]
图 5 PVDF/低维碳材料薄膜的非线性光学性能。(a)不同氧化还原石墨烯浓度下的 PVDF/RGO薄膜光限制图[93];(b)单一 PVDF与 PVDF/RGO 纳米聚合物薄膜的紫外-可见光透射谱[100];(c)不同多壁碳纳米管掺杂浓度下的PVDF/多壁碳纳米管复合薄膜透明照片;(ⅰ)单一PVDF,质量分数分别为(ⅱ)1%,(ⅲ)2%,(ⅳ)5%[101]; (d)CQDs掺杂的PVDF改性薄膜在紫外辐照200 h 前后透射率对比图[104]
Figure 5. NLO properties of PVDF/low-dimensional carbon materials films. (a) Optical limiting graphs for PVDF/RGO films with different concentrations of RGO[93]; (b) transmittance of pristine PVDF and PVDF-RGO nanocomposites[100]; (c) transparency camera image for PVDF/MWCNT composites films[101] with different concentration of MWCNT: (ⅰ) pure PVDF, quality score is (ⅱ) 1%, (ⅲ) 2%, (ⅳ) 5%; (d) transmittance of the modified CQDs/PVDF nanocomposite films before and after 200 h of UV exposure [104]
图 6 无机非金属晶体材料、金属盐及复合填料掺杂的PVDF薄膜非线性光学特性。(a)PVDF(TTTT)接枝在埃洛石纳米管上的构型示意[107];(b)PVDF@SiO2@S1扫描电镜图[113];(c)PVDF/埃洛石纳米管复合薄膜的归一化透射率(不同掺杂浓度下Z -扫描曲线)[107];(d)单一PVDF与PVDF/钛酸锂纳米复合薄膜的折射率变化图[111];(e)不同浓度 MoS2掺杂的PVDF薄膜直接带隙曲线[117];(f)TiO2掺杂多壁碳纳米管/PVDF 复合薄膜的傅里叶红外透射谱[123]
Figure 6. NLO properties of PVDF films doped with inorganic nonmetallic crystals, metallic salts, and composite fillers. (a) Schematics of TTTT(PVDF) configuration on HNTs[107]; (b) SEM micrographs of PVDF@SiO2@S1[113]; (c) transmittance of the PVDF/ HNTs films with Overlaid Z-scan curves[107]; (d) refractive index for pure PVDF and Li4Ti5O12/PVDF nanocomposites[111]; (e) direct bandgap of the MoS2 doped in PVDF nanocomposite samples[117]; (f) FTIR spectrums of TiO2@MWCNTs/PVDF composites[123]
图 7 PVDF及其共聚物薄膜的量子化学计算。(a)Ag/PVDF复合材料1250大原子系统模拟元胞,银原子灰色,氟原子蓝色,碳原子红色,氢原子绿色[131];(b)Ag/PVDF纳米复合材料的反射率R:(i)与(ii)表示入射光沿z轴与x轴,(iii)表示真空中Ag纳米颗粒沿z轴和x轴入射[131](c)上图为非极性α相→极性γ、β相的跃迁路径,下图为PVDF的α相TGTG链转变为β相的全T链时,分子链二面角变化,红色箭头表示偶极矩的方向,而黑色双箭头表示几何级数[130];(d)PVDF的折射率与(e)色散计算值,a、b、c 分别代表光子沿a、b、c轴的极化方向[70];(f)PVDF(九相晶体结构)折射率的理论计算值[132]
Figure 7. Quantum chemical calculation for PVDF and its copolymers films. (a) Snapshot of a Ag/PVDF1250 nanocomposites simulation cell. Silver atoms are shaded gray, fluorine blue, carbon red, and hydrogen green[131]; (b) the normal reflectance (R) of Ag/PVDF nanocomposites materials: (i) and (ii) are incident light along the z- and x-axes; (iii) present the respective optical properties of Ag-nanoparticles in vacuum, with incident fields along the z- and x-axes[131]; (c) the two-step transition pathway connecting the nonpolar α phase and the polar γ and β phases, the top panels show the conversion to the γ phase through a rotation of one chain, the bottom panel illustrates dihedral angle changes in the TGTG chain as it transforms to the T chain of the β phase. Red arrows indicate the directions of the dipole moments while black double arrows indicate the geometrical progression[130]; (d) calculated dispersion curves for the d-coefficients and (e) the refractive indices of PVDF. Labels a, b, and c represent the photon polarization directions along the crystal axes a, b, and c, respectively;[70] (f)theoretically calculated refractive index of PVDF[132]
表 1 PVDF及其共聚物薄膜的光学性能相关参数
Table 1. Optical characteristics of PVDF and its copolymer films
Refractive
indexsecond-harmonic
coefficientsIntrinsic Birefringences[51] Coherent
wavelengthgFibers α(Ⅱ) β(Ⅰ) γ(Ⅲ) a1.42[51]
a1.425[46]
a1.41−1.49[54]
b1.408[71]
b1.404−1.540[68]
a1.99[69]
a1.4−1.9[55]d33: 0.22 pm/V [52]
d31: 0.05 pm/V[52]
b−35 pm/V[55]
bd33: −40 pm/V[60];
bd33: −20±2 pm/V[60 ];
cd33: 1.66 pm/V[70]
cd31: 2.01 pm/V[70]0.0302 d0.0236 0.030773 0.001022 30 μm[46]
37 μm
(±3 μm)[52]e0.0236 0.030773 0.001022 0.0387 f0.0950 0.1132 0.0739 c0.0082[70] electro-optic coefficients(EO) Elasto-optic coefficients quadratic electro-optic coefficients $\left| {r_{51}^x } \right|$ [50]0.10×10−12 mV−1 $ \left| {\mathop \pi \nolimits_{11}^E - \left( {{\raise0.7ex\hbox{${\mathop n\nolimits_2^3 }$} \mathord{\left/ {\vphantom {{\mathop n\nolimits_2^3 } {\mathop n\nolimits_1^3 }}}\right.} \lower0.7ex\hbox{${\mathop n\nolimits_1^3 }$}}} \right)\mathop \pi \nolimits_{12}^E } \right| $ [50]3.6×10−12m2N−1 $ \left| {\mathop g\nolimits_{44}^x } \right| $ 0.02 m4C−2 [50] [70] 0.23×10−12 mV−1 21 m4C−2[59] $\left| {r_{42}^x } \right|$ [50]0.21×10−12 mV−1 $ \left| {\mathop h\nolimits_{55}^x } \right| $ 6.8×10−23 m2V−2[50] [70] 1.78×10−12 mV−1 4.11×10−18 m2V−2[59] $ \left| {\mathop r\nolimits_{13}^x - \left( {{\raise0.7ex\hbox{${\mathop n\nolimits_2^3 }$} \mathord{\left/ {\vphantom {{\mathop n\nolimits_2^3 } {\mathop n\nolimits_1^3 }}}\right.} \lower0.7ex\hbox{${\mathop n\nolimits_1^3 }$}}} \right)\mathop r\nolimits_{23}^x } \right| $ [50]0.38×10−12 mV−1 $ \left| {\mathop \pi \nolimits_{21}^E - \left( {{\raise0.7ex\hbox{${\mathop n\nolimits_2^3 }$} \mathord{\left/ {\vphantom {{\mathop n\nolimits_2^3 } {\mathop n\nolimits_1^3 }}}\right.} \lower0.7ex\hbox{${\mathop n\nolimits_1^3 }$}}} \right)\mathop \pi \nolimits_{22}^E } \right| $ [50]1.8×10−12 m2N−1 $ \left| {\mathop g\nolimits_{13}^x - \left( {{\raise0.7ex\hbox{${\mathop n\nolimits_2^3 }$} \mathord{\left/ {\vphantom {{\mathop n\nolimits_2^3 } {\mathop n\nolimits_1^3 }}}\right.} \lower0.7ex\hbox{${\mathop n\nolimits_1^3 }$}}} \right)\mathop g\nolimits_{23}^x } \right| $ [50]0.01 m4C−2 [70] 1.48×10−12 mV−1 $ \left| {\mathop h\nolimits_{13}^x - \left( {{\raise0.7ex\hbox{${\mathop n\nolimits_2^3 }$} \mathord{\left/ {\vphantom {{\mathop n\nolimits_2^3 } {\mathop n\nolimits_1^3 }}}\right.} \lower0.7ex\hbox{${\mathop n\nolimits_1^3 }$}}} \right)\mathop h\nolimits_{23}^x } \right| $ [59]26×10−23 m2V−2 a: Preparation with Spin-coating; b: Preparation with LB method; c. Calculations based on the formalism of Hughes and Sipe; d: Calculations based on Bunn, Denbigh (C-C, C-H) and Denbigh (C-F); e: Calculations based on Bunn, Denbigh (C-C, C-H) and Vogel(C-F); f: Calculations based on Denbigh (C-C, C- H) and LeFevre and LeFevre (C-F). g: Birefrigence of Melt-Spun PVDF Fibers before (above) and after (below) the poled films (Clod-Drawing, Elongated-40%) 表 2 PVDF-金属氧化物纳米聚合物薄膜的线性及非线性光学相关参数
Table 2. Linear optical and nonlinear optical parameters of PVDF/MO (metallic oxide) nanocomposites films
Nonlinear optical parameters Samples Leff β εr n2 ΔΦ0 Ed (eV) Ei (eV) Ea(eV) |χ(3)| P/ZnO [81] 1.051[81]
0.2339~0.30405[73]1.942[81]
17.58~2.064[73]3.15~4.91[81] −1.624[81]
−4.562~
12.22[73]0.181[81]
0.147~
0.29[74]5.57~4.95[73]
3.24[81]4.76~3.35[73] 1.16[73] 0.7145[73] P/ZnO/CuO [81] 0.862 4.740 — −3.220 0.294 — — — 1.4039 Samples β' εr n p Ed (eV) Ef (eV) ᴧ P/ZrO2[69] 3396.8~26.10 3.97~5.83 1.99~2.41 1.62~7.27 1.53~5.89 2.94~0.76 0.34~9.29 Linear optical parameters Samples εr n k Samples T εr P/CrO2[83] 2.77−5.83 1.395~1.43 0.005~0.03 P/Gd2O3: Eu3+[89] 82%~85% 7~7.5 P/PPO/POPOPGd2O3:Eu3+[89] 75%~77% 12~15 Samples[82] α εr Ed (eV) Samples[76] α Ed (eV) Ei (eV) P/PEO-Al2O3 0.99 3.56~6.35 4.91 P/PMMA-V-ZnO 0.88~0.60[78] 2.8 2.5 P/PEO-SnO2 0.99 2.7~4.68 4.62 P/PMMA-S-ZnO 0.82~0.60[78] 3.0 2.8 P/PEO-TiO2 0.982 3.08~5.05 3.53 P/PMMA-Dy-ZnO 0.78~0.60[78] 2.5 2.2 Samples α n Ed (eV) Ei (eV) k(10−2) T εr P/PMMA-ZnO [78] 0.975~0.602 [78]
0.83~0.40[76]1.29~1.54[78] 5.22~5.75[78]
2.9[76]2.6[78] 0.018~0.06[78] 35%~40%[78] 2.37~1.67[78] P/PMMA [78] 0.44[78]
0.50~0.35[76]1.21~1.22[78] 5.85[78]
4.4[76]3.7[76] 0.01[76] 65%~70%[76] 1.46[76] Samples α εr Ed (eV) Ea(eV) Samples α La2O3/P-TrFE[85] 0.968~0.996 163 3.15~2.80 10.20~0.15;20.84~0.41 P/Nd2O3[88] 0.90 — Fe3O4/P-HFP[87] 0.90 Note:P-PVDF, 1- ac activation energy (Eac), 2-dc activation energy (Edc), Ed-Direct band gap, Ei-Indirect optical band gap, n-linear refractive index (λ≈633 nm), Ea-optical activation energy, Ef-Fermi energy, n2-nonlinear refractive index (cm2/W×10−13), β-nonlinear absorption coefficient (two-photon, cm/W×10−8), α-linear absorption coefficient, transmittance, εr-dielectric constant, χ(3)-third order nonlinear optical susceptibility(10-6esu), Leff-effective length of the sample(10−3 cm), ΔΦ0-the nonlinear phase shift, k-the extenction coeffecient (λ≈633 nm), p-average polarizability (C2 m2J−1×10−39), β′-first hyperpolarizability(C3 m3J−2×10−51), ᴧ-anisotropy (C2 m2J−1×10−39), V-ZnO: ZnO doped with vanadium, S- ZnO: ZnO doped with sulfur, Dy-ZnO:ZnO doped with dysprosium. 表 3 PVDF/低维碳材料纳米聚合物薄膜的线性及非线性光学相关参数
Table 3. Linear optical and nonlinear optical parameters of PVDF/low-dimensional carbon materials nanocomposites films
Nonlinear optical parameters samples β n2 Pth Imχ(3) |χ(3)| P/RGO[99] 195−400 3.410−6.270 8.4−7.84 6.19−12.95 6.2−12.96 Linear optical parameters samples α n Ed (eV) Ei (eV) T P/RGO[100] 83%−99% 1.8−2.2 5−4.3 4.4−3.2 30%−1% PVDF/CQDs[105] 90%−98.5% 1.22−1.55 2.96−5.00 1.16−4.32 4%−12% samples T P-OH@CQDs/PVA [104] 88%(300−800 nm) PVDF/MWCNT[101] 0(5%CNT)、22%(2%CNT)、48%(1%CNT) Note:P-PVDF, Ed-direct band gap, Ei-indirect optical band gap, n-linear refractive index (λ≈633 nm), n2-nonlinear refractive index (cm2/W×10−10), β-Nonlinear absorption coefficient (two-photon, cm/GW), α-linear absorption coefficient, T-transmittance (λ≈633 nm), χ(3): third-order nonlinear optical susceptibility (10−11 esu), Imχ(3); The imaginary part of third-order nonlinear optical susceptibility (10−11 esu), Pth-optical limiting threshold power (MW/cm2). 表 4 PVDF/无机非金属晶体材料聚合物薄膜的线性及非线性光学相关参数
Table 4. Linear optical and nonlinear optical parameters of PVDF/inorganic nonmetallic crystalline materials nanocomposites films
Nonlinear optical parameters samples Δφ0 Leff n2 χ3 Pristine PVDF[107] 2.05 24.3 −3.13 −1.7872 P/HNT[107] 0.59−2.2 13.9−20.4 1.24−4.89 1.2075−8.9922 samples n∞ λ0(nm) S0 ε∞ N/m* ωp Li4Ti5O12[111] 2.78 213.62 1.47 8.15 0.472 4.09 P/Li4Ti5O12[111] 3.50−7.32 269.68−291.60 1.55−6.19 15.64−74.83 3.684−35.60 8.25−11.67 Linear optical parameters Samples α Ei (eV) 200 nm<λ<400 nm 400 nm<λ<800 nm BaTiO3[110] 0.99 0.684 3.6 (0.8)PVDF/(0.2)BaTiO3[110] 0.999 0.997 2.9 0.6PVDF/0.4BaTiO3[110] 0.999 0.999 2.4 1PVDF/5BaTiO3[109] 0.9−0.5 0.2−0.5 3.85−3.3 Note:P-PVDF, Ed−Direct band gap, Ei−Indirect optical band gap, n-Linear refractive index (λ≈633 nm), n2− nonlinear refractive index (cm2/W×10−12), T-transmittance (λ≈633 nm), χ(3): third-order nonlinear optical susceptibility (10−8esu), α-linear absorption coefficient, Pth−optical limiting threshold power (MW/cm2), Leff: the effective length (μm); Δφ0: the on-axis nonlinear phase shift at the focus; n∞: the long wavelength refractive index, λ0: the average oscillator wavelength, S0: average oscillator strength (1014 m−2), ε∞: high-frequency dielectric constant, N/m*: free carriers ratio (×1057 m−3), ωp: the plasma frequency (1014 s−1), n-Linear refractive index (λ≈633nm), k-the extension coefficient (10−3, 220 nm<λ<380 nm). -
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