Ligand Shell Engineering to Achieve Optimal Photoalignment of Semiconductor Quantum Rods for Liquid Crystal Displays

Zhang, Wanlong; Prodanov, Maksym F.; Schneider, Julian; Gupta, Swadesh Kumar; Dudka, Tetiana; Vashchenko, V. V.; Rogach, Andrey L.; Srivastava, Abhishek Kumar

doi:10.1002/adfm.201805094

Cited by 26 publications

(21 citation statements)

References 57 publications

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“…Particularly, for liquid crystal displays (LCD), unidirectionally aligned QRs are very promising as an enhancement film (QREF) for display backlight unit (BLU) replacing quantum dot enhancement films (QDEFs). [ 21–24 ] Because of the polarized emission, and higher light out‐coupling coefficients, QRs improve the overall optical efficiency of LCDs. [ 21,22,25 ] Three possible configurations have been explored for the QD‐based BLU for LCDs: i) edge optics proposed by QD Vision (Massachusetts), ii) QDEFs proposed by Nanosys (California); and iii) a QD‐on‐chip design proposed by LumenMax Optoelectronics (Taiwan).…”

Section: Introductionmentioning

confidence: 99%

Thermally Stable Quantum Rods, Covering Full Visible Range for Display and Lighting Application

Prodanov

Gupta

Kang

et al. 2020

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Recently, quantum rods (QRs) have been studied heavily for display and lighting applications. QRs offer serious advantages over the quantum dots such as higher light out‐coupling coefficient, and polarized emission. The QR enhancement films double liquid crystal display efficiency. However, it is still a challenge to synthesize good quality green (λem ≈ 520 nm) and blue (λem ≈ 465 nm) emitting QRs, due to very large bathochromic shift during the shell growth. Furthermore, until now, the presence of cadmium in high‐quality QRs is inevitable, but due to its toxicity, RoHS has restricted the amount of cadmium in consumer products. In this article, low Cd core‐shell QRs, with a narrow‐band luminescence spectrum tuned in the whole visible range, are prepared by replacing Cd with Zn in a one‐pot post‐synthetic development. These QRs possess the good thermal stability of photoluminescence properties, and therefore, show high performance for the on‐chip LED configuration. The designed white LEDs (WLEDs) are characterized by a high brightness of 120000 nits, and color gamut covering 122% NTSC (90% of BT2020), in the 1931CIE color space. Additionally, these LEDs show a high luminous efficiency of 115 lm W−1. Thus, these quantum rod LED are perfectly viable for display backlighting and lighting applications.

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Section: Introductionmentioning

confidence: 99%

Thermally Stable Quantum Rods, Covering Full Visible Range for Display and Lighting Application

Prodanov

Gupta

Kang

et al. 2020

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“…The QR ligands employed in this study are a mixture of longer octadecylphosphonic acid and shorter hexylphosphonic acid, with the ratio around 1:2. In the previous related study, it was shown that shorter ligands provide some space for the LCM to interpenetrate and interact with longer ligands …”

Section: Resultsmentioning

confidence: 99%

Formulation of a Composite System of Liquid Crystals and Light‐Emitting Semiconductor Quantum Rods: From Assemblies in Solution to Photoaligned Films

Dudka

Zhang

Schneider

et al. 2019

Adv Materials Technologies

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QRs), [4,5] have been considered as promising light-emitting components in modern display, lighting, bioimaging, and photonics applications. [6][7][8][9][10][11][12][13][14][15][16] Based on the quantum-confinement effect, these nanocrystals possess outstanding optical properties, such as precisely tunable emission, narrow emission bandwidths, high photoluminescence (PL) quantum yields (QYs), and better photostability compared to molecular dyes. [17][18][19] In addition, 1D anisotropic nanocrystals, such as CdSe/CdS core/shell QRs with a dot-in-rod geometry, show strongly polarized absorption and emission along the long axis of the QR. [20][21][22] The ability of strongly emitting semiconductor QR, when macroscopically aligned, to emit linearly polarized light makes them perfect candidate for liquid crystal display (LCD) backlights. To translate their anisotropic properties from a single nanocrystal to the macroscopically polarized lightemitting materials, QRs need to be oriented unidirectionally in plane, which can be achieved by several assembly approaches. [23][24][25][26][27] Our previous work has introduced photoinduced alignment of QRs in a liquid crystal polymer (LCP) matrix as a strategy to control QR orientation from centimeter [28] down to micrometer domain sizes. [29] By utilizing the photoactive sulfonic azo dye as an alignment layer, photo alignment is transferred to the liquid crystal monomers (LCM), whose reorientation results in torque that is transferred to the QRs through the repulsive interactions with the QR capping ligands. In general, the longchain organic ligands are used to protect/functionalize the surface and increase the steric repulsion of semiconductor QRs. It was observed that in the QR/LCM composite systems, the interaction of the QR ligands with the molecular LC matrix often leads to topological defects in the QRs/LCP composite films, which also depends on the concentrations of both nanoparticles and LCM in solution. [30][31][32][33][34] On one hand, for the low concentration of LC molecules, the orientational forces do not notably contribute to the aggregation process, but the interaction due to the change of the order parameter near the QR surface plays an important role. [35,36] This process also induces deformation of the LC director along the surface of the colloid The ability of strongly emitting semiconductor quantum rods (QRs), when macroscopically aligned, to emit linearly polarized light makes them the perfect candidate for liquid crystal (LC) display backlights. Macroscopic QR ordering is previously demonstrated by photoalignment of QR composites with polymerizable LC monomers. In this study, it is demonstrated that the optimum concentration of LC monomers and core/shell CdSe/CdS QRs enabling someone to achieve their uniform homogeneous orientation in photoaligned films strongly depends on the lengths and aspect ratios of the QRs. By aligning QRs with different aspect ratios ranging from 3 to 10, the best performance is achieved for shorter QRs with lengths of 11 and 31 ...

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“…However, many practical applications rely on device-scale, tuneable polarized luminescence from thin films of QDs, which requires the formation of anisotropic, configurable assemblies with longrange order ranging from nm to mm scales. 16 Over the last two decades several tools and methods to obtain ordered, thin films of QDs (often referred to as superlattices, SL) were developed. [17][18][19][20] In the case of anisotropic nanocrystals unidirectional alignment of QDs in SL is required to coherently enhance the intrinsic directional properties of individual QDs and achieve macroscopically anisotropic fluorescence.…”

Section: Introductionmentioning

confidence: 99%

“…These QDs/LC nanocomposites allow for ordered QDs thin-film tuneability, long-range order, and exhibit directional optical properties, making them interesting for applications as low-cost ondemand single photon sources or energy-efficient displays. 16,[34][35][36][37] However, one of the key parameters determining optical quality of these devices is compatibility between the ligand shell of quantum dots and the LC matrix. 16,38,39 Along this line, several groups have recently demonstrated that precise control of the architecture of the ligand shell can lead to enhanced dispersion or tuneable organization of QDs in the LC matrix 36 , however further research on QDs/LC matrix interactions is required to fully captitalize on the potential of these devices, e.g.…”

Section: Introductionmentioning

confidence: 99%

Thermomechanically controlled fluorescence anisotropy in thin films of InP/ZnS quantum dots

et al. 2021

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Ligand Shell Engineering to Achieve Optimal Photoalignment of Semiconductor Quantum Rods for Liquid Crystal Displays

Cited by 26 publications

References 57 publications

Thermally Stable Quantum Rods, Covering Full Visible Range for Display and Lighting Application

Thermally Stable Quantum Rods, Covering Full Visible Range for Display and Lighting Application

Formulation of a Composite System of Liquid Crystals and Light‐Emitting Semiconductor Quantum Rods: From Assemblies in Solution to Photoaligned Films

Thermomechanically controlled fluorescence anisotropy in thin films of InP/ZnS quantum dots

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