The Role of Rubrene Concentration on Dielectric Parameters of Nematic Liquid Crystal

In this study, the dielectric parameters of E7 coded nematic liquid crystal (NLC) composites containing the different amounts of rubrene fluorescent dye were investigated. E7, E7+0.5 wt.% Rubrene, and E7+1.0 wt.% Rubrene samples were prepared. Frequency dependent dielectric constants (ɛ′ and ɛ′′), dielectric anisotropy (Δε′), and ac conductivity (σac) graphs of rubrene doped E7 NLC composites were obtained by dielectric spectroscopy method and compared with pure E7 NLC. By using these graphs, relaxation frequency (fR), relaxation time (τR), dielectric strength (δɛ′), and crossover frequency (fc) parameters of the E7 NLC and its rubrene doped composites were determined. An increase in fR from 3.045 MHz to 3.697 MHz for 0 V and from 627 kHz to 686 kHz for 40 V was observed with increasing rubrene concentration. On the other hand, a decrease in τR from 0.052 μs to 0.043 μs for 0 V and from 0.254 μs to 0.232 μs for 40 V was seen with increasing rubrene concentration. Furthermore, an increase in fc from 1.145 MHz to 1.298 MHz was obtained with increasing rubrene concentration. The results show that the dielectric parameters change with the concentration of rubrene and it is thought that this study will provide a basis for investigating the dielectric properties of rubrene doped NLC composites. Moreover, it is concluded that the produced composites are a suitable base material for electro-optical device applications such as smart displays, photonics and electrical circuit elements

Effects of CdTe Quantum Dot Dispersal on Current-Voltage Characteristics in Liquid Crystalline Mediums of E63, E7 and SCLP

The usage of nano-sized quantum dots (QDs) particularly in guest-host based hybrid mediums revealed enhancements in electro-optical properties of the mediums, therefore the focus of considerable amount of contemporary studies has been about dispersal of QDs for improvements in medium. This study investigates the effects of CdTe QD dispersal on current-voltage characteristics of some liquid crystalline materials such as E63, E7 and SCLP. Current is increased for all samples due to QD dispersal, however the best improvement is obtained for E7. Hence, current-voltage characteristics of E7 and QD dispersed E7 mediums were also investigated under UV light exposure. Current values of both mediums were found to increase with increasing UV light power due to generation of electron-hole pairs. Photocurrent’s dependence on light power revealed that QD dispersal does not affect recombination mechanism in the medium. On the other hand, UV light responsivity of QD dispersed E7 was obtained approximately twice of that of E7. Thus, it was concluded that CdTe QDs make considerable contribution to current-voltage and photoconductivity characteristics of E7 in dark and under UV light illumination

Investigation of electro-optic and dielectric properties of CdSeS/ZnS quantum dot-doped 5CB nematic liquid crystals

YÖK Tez No: 523067Bu çalışmada, CdSeS/ZnS kuantum nokta katkılı 5CB (4-pentyl-4'-cyanobiphenyl) nematik sıvı kristal yapının elektro-optik ve dielektrik özellikleri incelenmiştir. CdSeS/ZnS kuantum nokta, 5CB nematik sıvı kristal içerisine ağırlıkça % 0,05, % 0,10 ve % 0,15 oranlarında katkılanmış ve sıvı kristal-kuantum nokta kompozit yapıları oluşturulmuştur. 5CB nematik sıvı kristal ve CdSeS/ZnS kuantum nokta katkılı 5CB nematik sıvı kristal kompozit yapıların elektrik ve dielektrik özellikleri 1 kHz-10 MHz frekans aralığında ve 0 V-20 V gerilim değerleri kullanılarak dielektrik spektroskopi tekniği ile incelenmiştir. Numunelerin optik özellikleri ise 300 nm-800 nm dalga boyu aralığında optiksel geçirgenlik spektroskopi yöntemi kullanılarak araştırılmıştır. Ölçüm sonuçlarından, 5CB nematik sıvı kristal ve CdSeS/ZnS kuantum nokta katkılı 5CB nematik sıvı kristal kompozit yapılara ait optik bant aralığı, kompleks dielektrik sabitinin reel ve sanal kısımları, dielektrik anizotropi, relaksasyon frekansı, geçiş frekansı, eşik voltajı, eğilme elastik sabiti ve relaksasyon zamanı parametreleri elde edilmiştir. Optik bant aralığı, eşik voltajı ve eğilme elastik sabiti parametrelerinin değerlerinin CdSeS/ZnS kuantum nokta katkılanması ile önemli ölçüde azaldığı gözlemlenmiştir. Ayrıca incelenen yapıların gerilime bağlı akım değerleri elde edilmiştir. Kuantum noktaların neden olduğu yük yoğunluğundaki artışa bağlı olarak, ortamdan geçen akım değerinin arttığı görülmüştür. Sonuçlar, CdSeS/ZnS kuantum noktaların 5CB nematik sıvı kristale katkılanması ile elde edilen kompozit yapılarda elektro-optik ve dielektrik özelliklerde önemli değişimlere neden olduğunu ve ortamın iletkenliğini arttırdığını göstermiştir.In this study, the electro-optic and dielectric properties of CdSeS/ZnS quantum dot doped 5CB (4-pentyl-4'-cyanobiphenyl) nematic liquid crystal structure were investigated. The CdSeS/ZnS quantum dot was doped into the 5CB nematic liquid crystal at a ratio of 0.05 %, 0.10 % and 0.15 % wt and liquid crystal-quantum dot composite structures were formed. Electric and dielectric properties of 5CB nematic liquid crystal and CdSeS/ZnS quantum dot doped 5CB nematic liquid crystal composite structures were investigated in the frequency range of 1 kHz-10 MHz and 0 V-20 V voltages with using dielectric spectroscopy method. The optical properties of the samples were investigated by optical transmission spectroscopy at a wavelength range of 300 nm-800 nm. The optical band gap, real and imaginary part of complex dielectric constant, dielectric anisotropy, the relaxation frequency, crossover frequency, threshold voltage, splay elastic constant and relaxation time parameters of 5CB nematic liquid crystal and CdSeS/ZnS quantum dot doped 5CB nematic liquid crystal composite structures were obtained using experimental data. The values of the optical band gap, threshold voltage and splay elastic constant parameters were found to decrease significantly with CdSeS/ZnS quantum dot doping. The voltage dependent current values of the investigated structures were also obtained. Depending on the increase in charge density caused by the quantum dots, the value of the current passing through the medium is increased. Results show that CdSeS/ZnS quantum dots cause significant changes in the electro-optic and dielectric properties of 5CB nematic liquid crystal composite structures and increase the conductivity of the mediums

Enhancement of electro-optical and dielectric properties of CdSeS/ZnS semiconductor quantum-dot-doped nematic liquid crystals in the presence of UV-illumination effect

WOS: 000468869000009In this study, we have investigated ultraviolet (UV) illumination effect on electro-optical and dielectric properties of varying concentration of CdSeS/ZnS semiconductor quantum-dot-doped 5CB nematic liquid crystal. Dielectric measurements were made from 10kHz to 10MHz frequency ranges in dark and under UV-illumination conditions. Electro-optical measurements were also performed with a voltage-dependence light transmission system at 10kHz frequency in dark and under UV-illumination conditions. Significant physical parameters such as relaxation frequency (f(R)), real and imaginary components of complex dielectric permittivity (epsilon and epsilon), and threshold voltage (V-th) values were obtained from experimental results. Results show that UV-illumination effects cause considerable improvements on electro-optical and dielectric characteristic of investigated samples.Duzce University Scientific Research ProjectDuzce University [2018.05.02.811]This work supported financially by Duzce University Scientific Research Project (Project No: 2018.05.02.811)

Investigation of Optical Band Gap of CdSeS/ZnS Quantum Dot Doped 5CB Nematic Liquid Crystals

Bu çalışmada, CdSeS/ZnS alaşım kuantum nokta katkılı 5CB (4-pentyl-4?-cyanobiphenyl) nematik sıvı kristal yapının optik bant aralığı değerleri incelenmiştir. CdSeS/ZnS alaşım kuantum nokta, 5CB nematik sıvı kristal yapı içerisine ağırlıkça % 0,05, % 0,1 ve % 0,15 oranlarında katkılanarak optik bant aralığı değerleri elde edilmiştir. Deneysel sonuçlara göre kuantum nokta katkılanmasıyla optik bant aralığı değerlerinin azaldığı gözlemlenmiştir. Elde edilen sonuçlar, CdSeS/ZnS alaşım kuantum nokta yapının sıvı kristal tabanlı cihaz uygulamalarında elektrooptik özellikleri değiştirebilen alternatif bir malzeme olarak kullanılabileceğini göstermektedirIn this study, optical band gap values of 5CB (4-pentyl-4 'cyanobiphenyl) nematic liquid crystal structure doped with CdSeS/ZnS alloyed quantum dots are investigated. The CdSeS/ZnS alloyed quantum dot was doped into the 5CB nematic liquid crystal structure at 0.05, 0.1 and 0.15 % wt/wt and optical band gap values were obtained. According to experimental results, optical band gap values decrease with quantum dot doping. The results show that the CdSeS/ZnS alloyed quantum dots can be alternative materials used in liquid crystal based device applications whose electro-optical properties are able to be easily modifie

Effect of intermolecular charge transfer between Ni(II)Pc and CdSeS/ZnS QD on dielectric relaxation mechanism of 5CB nematic liquid crystals in the presence of UV illumination

WOS: 000512889300085This paper is a report on electro-optical and dielectric parameters of Ni(II)Pc (nickel(II) phthalocyanine) and CdSeS/ZnS (cadmium selenide sulfide/zinc sulfide) quantum dot (QD) doped 5CB (4-pentyl-4 '-cyanobiphenyl) nematic liquid crystal (LC) in the dark and under UV illumination condition. Electro-optical and dielectric measurements of the samples were carried out using electro-optical switching and dielectric spectroscopy methods, respectively. Dielectric anisotropy, relaxation frequency, dielectric strength, and threshold voltage values were determined using the experimental data. Investigation of dielectric properties demonstrates that relaxation frequency is decreased because of the dispersal of Ni(II)Pc and CdSeS/ZnS QD under UV exposure. The electro-optical investigation also shows that UV illumination and dispersal of Ni(II)Pc and CdSeS/ZnS QD cause a decrease in threshold voltages. Overall, results indicate that Ni(II)Pc, CdSeS/ZnS QD and UV light enhanced the electro-optical and dielectric properties of 5CB nematic LC

Determination of Phase Transition and Electro-optical Behaviors of Quantum Dot Doped Polymer Dispersed Liquid Crystal

This paper describes our research into phase transition, electro-optical and dielectric behaviors of polymer dispersed liquid crystal (PDLC) and cadmium selenide sulphide/zinc sulphide quantum dot (QD) doped PDLC (PDLC/QD). The PDLC was prepared with nematic liquid crystal (E63) and UV-curable photopolymer (NOA65) by using a polymerization induced phase separation technique. Dielectric properties of composites were investigated with a dielectric/impedance analyzer at 1 kHz–10 MHz frequency range. Electro-optical measurements of investigated samples were carried out using an electro-optical switching method. Phase transition temperature of PDLC and PDLC/QD composites was also determined, using a differential scanning calorimeter. The results showed that the introduction of QD significantly changes the physical properties of PDLC, and these changes could become a focus of interest for future applications. © 2020, The Minerals, Metals & Materials Society

Electro-optical and dielectric performance analysis: the influence of azo dye on polymer/LC composite structures

WOS: 000453519000001In the present work, electro-optical and dielectric properties of polymer/LC doped with azo dye methyl red (MR) were investigated. Norland optical adhesive (NOA65) and nematic liquid-crystal (E63-coded nematic liquid crystal) materials were used to compose of polymer/LC composite structure. A doping agent ratio of MR was chosen 1% wt/wt in polymer/LC composite structure. Dielectric measurements of the obtained samples were held between 10Hz and 10MHz at room temperature using dielectric/impedance analyzer. Physical parameters such as dielectric permittivity, dielectric anisotropy, electric modulus, loss tangent, relaxation frequency, relaxation time, threshold voltage, and splay elastic constant were obtained from experimental data. Optical bandgap values of polymer/LC and polymer/LC/MR composite structures were estimated using UV spectroscopy technique. Polymer/LC composite structures' electro-optical properties were affected the MR dispersal which was reduced the anchoring force between polymer and LC molecules; therefore, threshold voltage and splay elastic constant decreased. In addition, dispersal of MR caused a decrease in optical bandgap values of polymer/LC composite structures. Due to the increase in charge density caused by MR, the value of the current passing through the polymer/LC composite structures increased as well as its dependence on voltage. Results show that MR dispersal enhanced electro-optical and dielectric properties of polymer/LC composite structures and makes it suitable to design new based on optoelectronic device applications.Duzce University Scientific Research ProjectDuzce University [2018.05.02.811]This work supported financially by Duzce University Scientific Research Project (Project No: 2018.05.02.811)

Dielectric properties of CdSeS/ZnS quantum dots doped PMMA/LC composite structure

WOS: 000484059200001In this work, electrical and dielectric properties of CdSeS/ZnS quantum dots (QDs) doped Polymer/Liquid Crystal composite structures (PMMA/LC) were investigated by using Dielectric Spectroscopy Technique in the frequency range of 100 Hz-10 MHz at room temperature. In order to determine the effect of quantum dot concentrations, PMMA/LC composites structure was dispersed with 0.5, 1 and 1.5 wt% CdSeS/ZnS QDs. Hence some considerable physical parameters such as dielectric constant (epsilon ' and epsilon ''), dielectric anisotropy (Delta epsilon '), relaxation frequency (f(R)), relaxation time (tau) as a function of frequency were obtained depend on QDs concentrations. Results show that QDs contribution have occurred significant changes in dielectric properties of investigated samples which can be used in PMMA/LC based device applications.Duzce University Scientific Research ProjectDuzce University [2019.05.02.920]DThis work was supported financially by Duzce University Scientific Research Project [Project No: 2019.05.02.920]

CdSeS/ZnS Kuantum Nokta Katkılı 5CB Nematik Sıvı Kristalinde Optik Bant Aralıklarının İncelenmesi

Bu çalışmada, CdSeS/ZnS alaşım kuantum nokta katkılı 5CB (4-pentyl-4′-cyanobiphenyl) nematik sıvı kristal yapının optik bant aralığı değerleri incelenmiştir. CdSeS/ZnS alaşım kuantum nokta, 5CB nematik sıvı kristal yapı içerisine ağırlıkça % 0,05, % 0,1 ve % 0,15 oranlarında katkılanarak optik bant aralığı değerleri elde edilmiştir. Deneysel sonuçlara göre kuantum nokta katkılanmasıyla optik bant aralığı değerlerinin azaldığı gözlemlenmiştir. Elde edilen sonuçlar, CdSeS/ZnS alaşım kuantum nokta yapının sıvı kristal tabanlı cihaz uygulamalarında elektro-optik özellikleri değiştirebilen alternatif bir malzeme olarak kullanılabileceğini göstermektedir