鹵化物非線性光學晶體合成與光學特性探討

(1)

國

立

交

通

大

學

機械工程學系

博士論文

鹵化物非線性光學晶體合成與光學特性探討

Synthesis and Characterization of Nonlinear Optical Halide

Crystals

研究生：林志光

指導教授：周長彬

(2)

鹵化物非線性光學晶體合成與光學特性探討

Synthesis and Characterization of Nonlinear Optical Halide Crystals

研究生：林志光 Student：Zhi-Guang Lin

指導教授：周長彬 Advisor：Chang-Pin Chou

國立交通大學

機械工程學系

博士論文

A Dissertation

Submitted to Department of Mechanical Engineering College of Engineering

National Chiao Tung University In Partial Fulfillment of the Requirements

for the Degree of Doctor of Philosophy

in

Mechanical Engineering March 2008

Hsinchu, Taiwan, Republic of China

(3)

I

中文摘要

本論文係採用化學合成法來成長光學非線性AGeX

3

(A = Rb, Cs;

X = Cl, Br)晶體，並藉由電子微探儀(EPMA)量測晶體成分比例、微差

掃描熱卡計(DSC)量測晶體相變溫度、粉末X光繞射儀(PXRD)量測晶

體結構、拉曼散射光譜儀(Raman)量測晶體振動型態、傅立葉紅外線

光譜儀(FTIR)量測晶體可穿透範圍、紫外光可見光光譜儀(UV-visible)

量測晶體能隙、光激發螢光光譜儀(PL)量測晶體發光特性、粉末二倍

頻(PSHG)量測晶體非線性係數、橢圓儀(ellipsometry)量測晶體折射係

數。由成分分析結果顯示，陰陽離子置換比例如同預期；且熱分析結

果顯示，晶體的居禮轉換溫度及熔點皆會隨著溴原子含量的增加而提

高，顯示所合成的AGeX

3

晶體皆以固溶體型態存在。從X光繞射結果

得知，

CsGe(Br

x

Cl

1−x

)

3

晶體結構會隨著溴原子含量的增加而歪斜扭

曲；但(Rb

z

Cs

1−z

)GeBr

3

晶體結構則是隨著銣原子含量的增加而朝正方

對稱結構變化。由拉曼散射光譜儀分析顯示，晶體的拉曼訊號會隨著

溴原子含量的增加而有紅位移的現象產生。而光激發螢光光譜分析顯

示，晶體的光激發光訊號會隨著晶體使用環境溫度的降低而有紅位移

的現象產生。紫外光可見光光譜儀分析顯示，陰離子取代的比例能調

變晶體能隙值的大小。而傅立葉紅外線光譜儀分析顯示，晶體的穿透

範圍會隨著溴原子含量的增加而擴大。由粉末二倍頻檢測結果得知，

晶體的二階非線性係數會隨著溴原子含量的增加而變大，但會隨著銣

原子含量的增加而變小。

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II

Abstract

In this thesis, we grow the NLO crystals by chemical synthesis. Most studies have examined the structural, linear optical and nonlinear optical properties of the AGeX3 (A = Rb, Cs; X = Cl, Br) crystals by varying the alloy composition to satisfy

the demands of specific applications.

In the analysis of EPMA, bromine replaced chlorine in CsGeCl3, and vice versa

in CsGeBr3 while cesium was substituted by rubidium in CsGeBr3. According to DSC

analysis, the Curie temperature and the melting temperature of the crystals rose with Br content.

The XRD analysis indicated that the structural distortion of CsGe(BrxCl1−x)3

(R3m) increases with Br content, while the structure of (RbzCs1−z)GeBr3 slowly

becomes centro-symmetric as Rb content increases. The results of Raman spectroscopy agree with the expectation based on effective-mass that the oscillation frequency increases as the Br content falls because Br is heavier than Cl. The atomic vibration modes of AGeX3 (A = Rb, Cs; X = Cl, Br) system were also defined herein.

Regarding transparency characteristics, the longest infrared transparency wavelength is typically limited by the phonon absorption of the crystal and the absorption edge is limited by the energy band-gap of the crystal. UV-visible spectra show that the absorption edge declines from 3.43 to 2.38 eV with the composition of bromine (x = 0 to 1), but remains constant for z = 0 to 3/4. The infrared phonon absorption edge of CsGe(BrxCl1−x)3 with x = 0 to 1 is approximately from 30 to 47 μm.

Hence, the transmission range of the crystals increases with Br. Furthermore, the force constant increases as the Br content declines, such that the oscillation frequency increases as Br content decreases. The photoluminence spectra revealed that the emission bands of CsGe(BrxCl1-x)3 and (RbzCs1-z)GeBr3 were red-shifted as the

temperature fell, because cooling reduced the lattice constant.

Detection of the generated second-harmonic of the powder demonstrates that all of the crystals, CsGe(BrxCl1-x)3 (x = 0, 1/6, 1/4, 2/6, 3/6, 4/6, 3/4, 5/6, 1) and

(RbzCs1-z)GeBr3 (z = 1/4, 2/4, 3/4), were phase-matchable. The structural distortion

and the off-center Ge ion in the unit cell govern the SHG responses. The XRD results that the lattice constant increased with Br content while the cell angle decreased as Br increased. Therefore, the structural distortion of CsGe(BrxCl1−x)3 increases with Br

content and the position of the B-site cation, Ge, becomes closer to the cell corner. However, (RbzCs1−z)GeBr3 yields opposing results as the Rb content is increased.

Thus, the nonlinearity properties increased with Br content, but fell as Rb content increased. This result is identical to that for PSHG, for which that second-order NLO susceptibility increased with Br content, but declined as Rb content increased.

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This dissertation is dedicated with love to

my mother and my friends.

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IV

List of Tables

Table 1-1 Conventional IR NLO crystals.···14 Table 3-1 The vibration modes of cubic ABO3 structure.···58

Table 3-2 The structures of perovskite and their vibration modes.···59 Table 3-3 The Raman spectra comparison for the ternary halides CsGe(BryCl1-y)3

(B-series). The descriptions of the peaks are: “vs” = very strong, “s” = strong, “ls” = less strong, “m” = middle, and “w” = weak. The unit of these Raman peaks was labeled as cm-1.···60 Table 3-4 The Raman spectra comparison for the ternary halides CsGe(BrxCl1-x)3

(C-series). The descriptions of the peaks are: “vs” = very strong, “s” = strong, “ls” = less strong, “m” = middle, and “w” = weak. The unit of these Raman peaks was labeled as cm-1.···61 Table 3-5 The Raman spectra comparison for the ternary halides CsGe(BrxCl1-x)3 and

(RbzCs1-z)GeBr3. The descriptions of the peaks are: “vs” = very strong, “s”

= strong, “ls” = less strong, “m” = middle, and “w” = weak. The unit of these Raman peaks was labeled as cm-1.···62 Table 4-1 The IR absorption/Raman spectra of CsGe(BryCl1-y)3 (B-series). The unit of

these Raman and FTIR peaks was labeled as cm-1. (P : Raman peak, V : FTIR valley)···115 Table 4-2 The IR absorption/Raman spectra of CsGe(BrxCl1-x)3 (C-series). The unit of

these Raman and FTIR peaks was labeled as cm-1. (P : Raman peak, V : FTIR valley)···116 Table 5-1 The ellipsometry measurements of the rhombohedral NLO crystals

CsGe(BryCl1-y)3 (B-series).···145

Table 5-2 The ellipsometry measurements of the rhombohedral NLO crystals CsGe(BrxCl1-x)3 (C-series).···145

Table 5-3 The ellipsometry measurements of the rhombohedral NLO crystals (RbzCs1-z)GeBr3.···145

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List of Figures

Fig. 2-1 The procedure of synthesizing raw rhombohedral nonlinear optical crystals

ABX3.···28

Fig. 2-2 The procedure of recrystallizing rhombohedral nonlinear optical crystals ABX3.···29

Fig. 2-3 The analyzing procedures.···30

Fig. 2-4 The scheme of the Raman system.···31

Fig. 2-5 The scheme of the PL system (optical pumping system).···32

Fig. 2-6 The scheme of the PSHG system.···33

Fig. 2-7 EPMA measurements, CsGe(BryCl1-y)3 (B-series) : y = 0, 1/6, 1/4, 2/6, 3/6, 4/6, 3/4, 5/6, 1.···34

Fig. 2-8 EPMA measurements, CsGe(BrxCl1-x)3 (C-series) : x = 0, 1/6, 1/4, 2/6, 3/6, 4/6, 3/4, 5/6, 1.···34

Fig. 2-9 EPMA measurements, CsGe(BrxCl1-x)3 : x = 0, 1/4, 2/4, 3/4, 1 and (RbzCs1-z)GeBr3 : z = 0, 1/4, 2/4, 3/4, 1.···35

Fig. 2-10 The thermal analysis of rhombohedral nonlinear optical crystals CsGe(BrxCl1-x)3.···36

Fig. 3-1 X-ray diffraction from 2-dimensional periodic lattices.···63

Fig. 3-2 Representation of the crystallographic planes hkl.···63

Fig. 3-3 The X-ray powder diffraction results for nonlinear optical crystals CsGe(BrxCl1-x)3.···64

Fig. 3-4 The X-ray powder diffraction results for nonlinear optical crystals CsGe(BrxCl1-x)3 and (RbyCs1-y)GeBr3.···65

Fig. 3-5 The X-ray diffraction angle of CsGe(BrxCl1-x)3 determined by experiment and simulation.···66

Fig. 3-6 The lattice constant of CsGe(BrxCl1-x)3 unit cell determined by experiment and simulation.···67

Fig. 3-7 The cell angle of CsGe(BrxCl1-x)3 unit cell determined by experiment and simulation.···68

Fig. 3-8 The cell volume of CsGe(BrxCl1-x)3 unit cell determined by experiment and simulation.···69

Fig. 3-9 Structural parameters of the NLO crystals CsGe(BrxCl1-x)3 and (RbyCs1-y)GeBr3.···70

Fig. 3-10 The cell volume of the NLO crystals CsGe(BrxCl1-x)3 and (RbyCs1-y)GeBr3.···71

Fig. 3-11 The unit cell of constituent atoms that are input to the calculation for

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CsGeCl3.···72

Fig. 3-12 The unit cell of constituent atoms that are input to the calculation for CsGe(Br1/6Cl5/6)3.···73

Fig. 3-19 The unit cell of constituent atoms that are input to the calculation for CsGeBr3.···80

Fig. 3-20 The X-ray diffraction results for CsGeCl3 determined by experiment and

simulation.···72 Fig. 3-21 The X-ray diffraction results for CsGe(Br1/6Cl5/6)3 determined by

experiment and simulation.···73 Fig. 3-22 The X-ray diffraction results for CsGe(Br1/4Cl3/4)3 determined by

experiment and simulation.···79 Fig. 3-28 The X-ray diffraction results for CsGeBr3 determined by experiment and

simulation.···80 Fig. 3-29 Idealised model of Rayleigh scattering and Stokes and anti-Stokes Raman

scattering.···81 Fig. 3-30 The point groups and symmetry axes of perovskite.···82

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Fig. 3-31 The vibration modes of octahedral structure. (a) Strengthing vibration, (b)

Bending vibration.···83

Fig. 3-32 The Raman spectrum of CsGe(BrxCl1-x)3 (R3m) crystals at room temperature.···84

Fig. 3-33 The Raman spectrum of CsGe(BrxCl1-x)3 and (RbyCs1-y)GeBr3 crystals at room temperature.···85

Fig. 3-34 The peak-splitting of CsGeCl3 (R3m) Raman spectrum.···86

Fig. 3-35 The peak-splitting of CsGe(Br3/6Cl3/6)3 (B-series) Raman spectrum.···87

Fig. 3-36 The peak-splitting of CsGe(Br3/6Cl3/6)3 (C-series) Raman spectrum.···87

Fig. 3-37 The peak-splitting of CsGeBr3 (R3m) Raman spectrum.···88

Fig. 3-38 The Raman vibrational modes of CsGe(BryCl1-y)3 (B-series) crystals at room temperature.···89

Fig. 3-39 The Raman vibrational modes of CsGe(BrxCl1-x)3 (C-series) crystals at room temperature.···90

Fig. 3-40 The Raman vibrational modes of CsGe(BrxCl1-x)3 and (RbzCs1-z)GeBr3 crystals at room temperature.···91

Fig. 4-1 Interband transitions in solids: (a) direct band gap, (b) indirect band gap. The vertical arrow represents the photon absorption process, while the wiggly arrow in part (b) represents the absorption or emission of a phonon.···117

Fig. 4-2 Band structure of a direct gap III-V semiconductor such as GaAs near k = 0. E = 0 corresponds to the top of the valence band, while E = Eg corresponds to the bottom of the conduction band. Four bands are shown: the heavy hole (hh) band, the light hole (lh) band, the split-off hole (so) band, and the electron (e) band. Two optical transitions are indicated. Transition 1 is a heavy hole transition, while transition 2 is a light hole transition. Transitions can also take place between the split-off hole band and the conduction band.···118

Fig. 4-3 Absorption coefficient near the band edge of CsGe(BryCl1-y)3 (B-series) plotted in coordinates α2 and hv. The inset shows the Br composition dependence of Eg obtained.···119

Fig. 4-4 Absorption coefficient near the band edge of CsGe(BrxCl1-x)3 (C-series) plotted in coordinates α2 and hv. The inset shows the Br composition dependence of Eg obtained.···120

Fig. 4-5 Absorption coefficient near the band edge of CsGe(BrxCl1-x)3 and (RbzCs1-z)GeBr3 plotted in coordinates α2 and hv. The inset shows the substituted composition dependence of Eg obtained.···121

Fig. 4-6 Types of molecular vibrations. Note: + indicates motion from the page toward the reader; - indicates motion away from the reader.···122

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Fig. 4-7 Potential energy diagrams. (a) Curve 1, harmonic oscillator. (b) Curve 2, anharmonic oscillator.···123 Fig. 4-8 The full transmission range of the nonlinear optical crystals CsGe(BryCl1-y)3

(B-series) (a) y = 1.0, (b) y = 0.86, (c) y = 0.78, (d) y = 0.70, (e) y = 0.52, (f) y = 0.35, (g) y = 0.27, (h) y = 0.19, (i) y = 0.···124 Fig. 4-9 The full transmission range of the nonlinear optical crystals CsGe(BrxCl1-x)3

(C-series) (a) x = 1.0, (b) x = 0.82, (c) x = 0.79, (d) x = 0.68, (e) x = 0.51, (f) x = 0.35, (g) x = 0.26, (h) x = 0.18, (i) x = 0.···125 Fig. 4-10 The transmission edge and absorption edge of nonlinear optical crystals

CsGe(BryCl1-y)3 (B-series).···126

Fig. 4-11 The transmission edge and absorption edge of nonlinear optical crystals CsGe(BrxCl1-x)3 (C-series).···126

Fig. 4-12 The Raman scattering versus IR absorption spectra of CsGe(BryCl1-y)3

(B-series). (a) y = 1.0, (b) y = 0.86, (c) y = 0.78, (d) y = 0.70, (e) y = 0.52, (f) y = 0.35, (g) y = 0.27, (h) y = 0.19, (i) y = 0.···127 Fig. 4-13 The Raman scattering versus IR absorption spectra of CsGe(BrxCl1-x)3

(C-series). (a) x = 1.0, (b) x = 0.82, (c) x = 0.79, (d) x = 0.68, (e) x = 0.51, (f) x = 0.35, (g) x = 0.26, (h) x = 0.18, (i) x = 0.···128 Fig. 4-14 The force constant of bonds between Cs+ and anion group Ge Br Cl( _x ₁₋_x)₃−1

of CsGe Br Cl( _x ₁₋_x)₃ crystals.···129 Fig. 5-1 The exciton dispersion in a two-particle (electron-hole) excitation diagram of

the entire crystal. The crystal ground state (zero energy and zero momentum) is the point at the origin. Different parabolas represent the kinetic energy bands associated with different terms of the excitonic series.···146 Fig. 5-2 Visualization of (a) an exciton bound to an ionized donor, (b) a neutral donor,

and (c) a neutral acceptor.···147 Fig. 5-3 PL spectra of CsGeBr3 under 325nm excitation (He-Cd laser, power = 4mW)

in the temperature range of 17 to 293K.···148 Fig. 5-4 Temperature dependence of the peak energy of emission bands A, B and K of CsGe(BrxCl1-x)3 crystals, (a) x = 1 (b) x = 5/6 (c) x = 4/6 (d) x = 3/6 (e) x =

2/6 (f) x = 1/6 (g) x = 0.···149 Fig. 5-5 Comparison of Br content dependent photon energy from emission band A with Br content dependent absorption edge from UV-visible spectra.···150 Fig. 5-6 PL spectra of CsGeBr3 annealed at 235oC for 0 to 36 hr under 325nm

excitation (He-Cd laser, power = 4mW) at 17K.···151 Fig. 5-7 Variation of PL intensity with reciprocal temperature for the emission band B

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of CsGeBr3.···152

Fig. 5-8 Variation of PL intensity with reciprocal temperature for the emission band B of CsGe(Br4/6Cl2/6)3 and CsGe(Br5/6Cl1/6)3.···153

Fig. 5-9 PL spectra of (RbyCs1-y)GeBr3 under 325nm excitation (He-Cd laser, power =

4mW) at 17K.···154 Fig. 5-10 Temperature dependence of the peak energy of emission bands A, B and K

of (RbyCs1-y)GeBr3 crystals.···155

Fig. 6-1 Example of second harmonic conversion efficiency as a function of the length of the nonlinear crystal for various coherence lengths.···182 Fig. 6-2 Quasi-phase matching. The sign of the nonlinear susceptibility is reversed

periodically with the period equal to the coherence length. Ps is the spontaneous polarization of the crystal.···183 Fig. 6-3 Schematic layout of the apparatus for use in the Kurtz powder

measurement.···184 Fig. 6-4 The typical response for powders of phase-matchable and non-matchable

crystals, showing the SHG as a function of particle size.···185 Fig. 6-5 The powder second-harmonic generation results for rhombohedral nonlinear

optical crystals CsGeBr3.···186

Fig. 6-6 The comparison of integrated powder second-harmonic generation intensity of nonlinear optical crystals KDP and CsGe(BryCl1-y)3 (B-series).···187

Fig. 6-7 The comparison of integrated powder second-harmonic generation intensity of nonlinear optical crystals KDP and CsGe(BrxCl1-x)3 (C-series).···188

Fig. 6-8 The comparison of integrated powder second-harmonic generation intensity of nonlinear optical crystals KDP, CsGe(BrxCl1-x)3 and

(RbzCs1-z)GeBr3.···189

Fig. 6-9 The effective powder second-harmonic generation coefficients and their energy bandgaps of nonlinear optical crystals CsGe(BrxCl1-x)3.···190

Fig. 6-10 The effective powder second-harmonic generation coefficients and their energy bandgaps of nonlinear optical crystals CsGe(BrxCl1-x)3 and

(RbyCs1-y)GeBr3.···191

Fig. 6-11 The nonlinearity of 2 _/

eff

d n_ω3 for nonlinear optical crystals

CsGe(BrxCl1-x)3.···192

Fig. 6-12 The nonlinearity of 2 _/

eff

d n_ω3 for nonlinear optical crystals CsGe(BrxCl1-x)3

and (RbyCs1-y)GeBr3.···193

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鹵化物非線性光學晶體合成與光學特性探討

國

立

交

通

大

學

機 械 工 程 學 系

博士論文

鹵化物非線性光學晶體合成與光學特性探討

Synthesis and Characterization of Nonlinear Optical Halide

Crystals

研 究 生：林志光

指導教授：周長彬

鹵化物非線性光學晶體合成與光學特性探討

Synthesis and Characterization of Nonlinear Optical Halide Crystals

研 究 生：林志光 Student：Zhi-Guang Lin

指導教授：周長彬 Advisor：Chang-Pin Chou

國 立 交 通 大 學

機 械 工 程 學 系

博 士 論 文

中文摘要

本論文係採用化學合成法來成長光學非線性AGeX

(A = Rb, Cs;

X = Cl, Br)晶體，並藉由電子微探儀(EPMA)量測晶體成分比例、微差

掃描熱卡計(DSC)量測晶體相變溫度、粉末X光繞射儀(PXRD)量測晶

體結構、拉曼散射光譜儀(Raman)量測晶體振動型態、傅立葉紅外線

光譜儀(FTIR)量測晶體可穿透範圍、紫外光可見光光譜儀(UV-visible)

量測晶體能隙、光激發螢光光譜儀(PL)量測晶體發光特性、粉末二倍

頻(PSHG)量測晶體非線性係數、橢圓儀(ellipsometry)量測晶體折射係

數。由成分分析結果顯示，陰陽離子置換比例如同預期；且熱分析結

果顯示，晶體的居禮轉換溫度及熔點皆會隨著溴原子含量的增加而提

高，顯示所合成的AGeX

晶體皆以固溶體型態存在。從X光繞射結果

得知，

CsGe(Br

Cl

)

晶體結構會隨著溴原子含量的增加而歪斜扭

曲；但(Rb

Cs

)GeBr

晶體結構則是隨著銣原子含量的增加而朝正方

對稱結構變化。由拉曼散射光譜儀分析顯示，晶體的拉曼訊號會隨著

溴原子含量的增加而有紅位移的現象產生。而光激發螢光光譜分析顯

示，晶體的光激發光訊號會隨著晶體使用環境溫度的降低而有紅位移

的現象產生。紫外光可見光光譜儀分析顯示，陰離子取代的比例能調

變晶體能隙值的大小。而傅立葉紅外線光譜儀分析顯示，晶體的穿透

範圍會隨著溴原子含量的增加而擴大。由粉末二倍頻檢測結果得知，

晶體的二階非線性係數會隨著溴原子含量的增加而變大，但會隨著銣

原子含量的增加而變小。

Abstract

This dissertation is dedicated with love to

my mother and my friends.

Table of Contents

List of Tables

List of Figures

機械工程學系

研究生：林志光

研究生：林志光 Student：Zhi-Guang Lin

國立交通大學

機械工程學系

博士論文