Optical Display Applications Research Articles

Liquid‐Crystal‐Powered Metasurfaces for Electrically and Thermally Switchable Photorealistic Nanoprinting and Optical Security Platform

AbstractActive or reconfigurable metasurfaces have been considered a promising paradigm for dynamic structural coloration and are starting to find their way into the ultra‐compact integrated optical display and color printing platforms. Generally, an ideal dynamic structural color platform requires full hue‐saturation‐brightness (HSB) control, high switching contrast, and a simple operation manner. Unfortunately, to date, it remains challenging to simultaneously achieve all these features using previous approaches. Here, a novel electrically and thermally switchable reflective nanoprinting platform is reported by integrating polarization‐sensitive silver nanogroove arrays with a twisted nematic LC cell. Compared to conventional LC‐assisted dynamic nanoprinting, the device can simultaneously achieve superior color purity, wider gamut, and higher switching contrast. Moreover, through the implementation of a sub‐pixels scheme, arbitrary colors in the color gamut can be created by a mixture of red, green, and blue (RGB) channels at different ratios. As a proof of concept, dynamic switching of photorealistic nanoprinting with full HSB control at a high pixel density (>4,000 pixels per inch) as well as information switching and steganography are demonstrated, suggesting that the device possesses great potential in optical display and information security applications.

Dipole-tunable interfacial engineering strategy for high-performance all-inorganic red quantum-dot light-emitting diodes

All-inorganic quantum dot (QD) light-emitting diodes (AI-QLEDs) with excellent stability received enormous interest in the past few years. Nevertheless, the vast energy offset and the high trap density at the NiOX/QDs interface limit hole injection leading to fluorescence quenching and hampering the performance. Here, we present self-assembled monolayers (SAMs) with phosphonic acid (PA) anchoring groups modifying NiOX hole transport layer (HTL) to tune energy level and passivate trap states. This strategy facilitates hole injection owning to the well-aligned energy level by interface dipole, downshifting the vacuum level, reducing the hole injection barrier from 0.94 eV to 0.28 eV. Meanwhile, it mitigates the interfacial recombination by passivating surface hydroxyl group (-OH) and oxygen vacancy (VO) traps in NiOX. The electron leakage from QDs toward NiOX HTL is significantly suppressed. The all-inorganic R-QLEDs exhibit one of the highest maximum luminance, external quantum efficiency and operational lifetime of 88980 cd m−2, 10.3 % and 335045 h (T50 @100 cd m−2), respectively. The as-proposed interface engineering provides an effective design principle for high-performance AI-QLEDs for future outdoor and optical projection-type display applications.

The synthesis and luminescence properties of Bi3+/Eu3+ co-doped Gd2O3 phosphors with high thermal stability and tunable emission via energy transfer

In this work, the highly monodisperse (Gd0.99-xBi0.01Eux)2O3 phosphors with spherical morphologies (∼170 nm) are successfully obtained through precursor synthesis via urea-based homogeneous precipitation (UBHP) method, followed by annealing at 1000 °C. The Bi/Eu-doped does not alter the crystal structure, and maintain the cubic structure of the Gd2O3 host. Owing to the Bi3+ occupies two different sites (C2, S6) in Gd2O3 of the cubic phase, the 1S0 → 3P1 transition of Bi3+ has two significant excitation bands (335 nm and 375 nm). By monitoring the excitation at 335 nm and 375 nm, the (Gd0.99-xBi0.01Eux)2O3 phosphors show both Bi3+ (420 nm and 530 nm) and Eu3+ (611 nm) emissions, respectively. The presences of Gd3+ and Bi3+ excitation bands on the PLE spectra by monitoring the Eu3+ emission indicate the Bi3+ → Eu3+ and Gd3+ → Eu3+ energy transfer, respectively, and the energy transfer efficiency is up to 99 %. Meanwhile, the energy transfer mechanism of the (Gd0.99-xBi0.01Eux)2O3 samples is dominated by the dipole-dipole interaction. Under two different excitation wavelengths, the emission intensity varies with the Eu3+ doping content and the quenching concentration is about 3 at%. The calculated value of the critical distance Rc is 12.12 Å, which indicates that the quenching mechanism is mainly caused by the multipole interaction. Meanwhile, the emission color can be tuned though adjusting the Eu3+ content. The temperature-dependent (in the range of 100–500 K) analysis has been obtained, the results indicate the (Gd0.99-xBi0.01Eux)2O3 samples have good thermal stability. The (Gd0.99-xBi0.01Eux)2O3 phosphors developed in this work is expected to be widely used in lighting and optical display applications.

Vectorial‐Manipulating Encryption for Multi‐Channel Capacity and Security Enhancement

AbstractEmerging meta‐optics unfold unprecedented capabilities in optical display, information storage, and encryption applications. Particularly, the recent advances in vectorial holography based on the multi‐parameter manipulation of the Jones matrix have increased the modulation space and information capacity. However, the fundamental degree of freedom (DoF) extreme limit in the optical encoding space of the Jones matrix bottlenecks the information capacity for high‐demand practical applications. To further expand the high‐volume encryption with enhanced security, here, a vectorial‐manipulating encryption strategy is proposed to originally demonstrate multi‐channel encryption and display. By ingeniously utilizing multi‐beam overlapping and precisely controlling their phase differences in the overlapping area, the capacity expansion of up to 12‐channel near‐/far‐field optical images is enabled. Such vectorial‐manipulating strategy is also applied to near‐field nanoprinting and realizes additional encrypted nanoprinting information. More intriguingly, the optical encryption will not be decrypted unless setting with a particular combination of input/output polarization keys, thus enhancing its concealment security beyond the conventional encryption. Overall, the proposed vectorial‐manipulating strategy expands the state‐of‐the‐art storage capacity with enhanced decipher security and potentially suggests a new path for the next‐generation optical storage and encryption security applications.

Ultrastable emissive perovskite nanocomposite via dual protection of polymer-grafted TS-1 zeolite for backlight display application

Instability of all-inorganic perovskite quantum dots (PQDs) driven by the inherent ionic nature poses a grand challenge towards their long-term stability in optoelectronic devices. Herein, we report the crafting of a highly stable dual-protected CsPbBr3 perovskite nanocomposite by capitalizing on the encapsulation of a hydrophobic Styrene-Divinylbenzene (St-Dvb) copolymer grafted hierarchical titanium silicalite-1 (TS-1) zeolite shell. Firstly, an optimal hot injection method was used to accommodate CsPbBr3 PQDs into hierarchical TS-1 zeolite. After the modification of terminated Si-OH groups on the surface of TS-1 by phenyltriethoxysilane (PTES), a subsequent polymerization of St and Dvb was implemented using azobisisobutyronitrile (AIBN) as initiator to result in the highly emissive CsPbBr3-TS@St-Dvb nanocomposite, exhibiting outstanding luminescent stability against heat, polar solvents, and UV light irradiation. The as-prepared CsPbBr3-TS@St-Dvb nanocomposite also showed strongly suppressed anion exchange and high compatibility in polymer matrix, enabling improved applicability for versatile lighting and optical display applications. Ultimately, a white light-emitting diode (WLED) composed of green-emitting CsPbBr3-TS@St-Dvb and red-emitting K2SiF6:Mn4+ phosphor onto a commercial blue InGaN LED chip with wide color gamut and excellent stability is demonstrated. This work highlights a judiciously-designed and hard-soft dual-protected strategy to produce ultrastable perovskite nanomaterials with high brightness and durability for backlight display application.

Multicolor and 3D Holography Generated by Inverse-Designed Single-Cell Metasurfaces.

Metasurface-generated holography has emerged as a promising route for fully reproducing vivid scenes by manipulating the optical properties of light using ultra-compact devices. However, achieving multiple holographic images using a single metasurface is still difficult due to the capacity limit of a single meta-atom. In this work, an inverse design method based on gradient-descent optimization is presented to encode multiple pieces of holographic information into a single metasurface. The proposed method allows the inverse design of single-cell metasurfaces without the need for complex meta-atom design strategies, facilitating high-throughput fabrication using broadband low-loss materials. By exploiting the proposed design method, both multiplane red-green-blue(RGB)colorand three-dimensional(3D) holograms are designed and experimentally demonstrated. Multiplane RGB color holograms with nine distinct holograms are achieved, which demonstrate the state-of-the-art data capacity of a phase-only metasurface. The first experimental demonstration of metasurface-generated 3D holograms with completely independent and distinct images in each plane is also presented. The current research findings provide a viable route for practical metasurface-generated holography by demonstrating the high-density holography produced by a single metasurface. It is expected to ultimately lead to optical storage, display, and full-color imagingapplications.

Optical Encryption in the Photonic Orbital Angular Momentum Dimension via Direct-Laser-Writing 3D Chiral Metahelices.

Vortex beams, which intrinsically possess optical orbital angular momentum (OAM), are considered as one of the promising chiral light waves for classical optical communications and quantum information processing. For a long time, it has been an expectation to utilize artificial three-dimensional (3D) chiral metamaterials to manipulate the transmission of vortex beams for practical optical display applications. Here, we demonstrate the concept of selective transmission management of vortex beams with opposite OAM modes assisted by the designed 3D chiral metahelices. Utilizing the integrated array of the metahelices, a series of optical operations, including display, hiding, and even encryption, can be realized by the parallel processing of multiple vortex beams. The results open up an intriguing route for metamaterial-dominated optical OAM processing, which fosters the development of photonic angular momentum engineering and high-security optical encryption.

Polarization Multiplexing Bifunctional Metalens Designed by Deep Neural Networks

AbstractAs planar optical elements, metasurfaces confer an unprecedented potential to manipulate light, which benefits from the deep control of the interactions between nanostructures and light. In the past decade, considerable progress has been made in various metasurfaces for on‐demand functions, drawing great interest from the scientific community. However, it is a great challenge to integrate different functions into a single metasurface, due to the incapability of manipulating light at different dimensions and the lack of universal intelligent design strategy. Here, an intelligent design platform based on deep neural networks is proposed, which can map between structure parameters and optical response. The well‐trained network model can intelligently retrieve nanostructures to meet multidimensional optical requirements of metasurfaces. Four metalenses for chiral focusing are realized by the design platform and the simulation results are highly consistent with the design target. In addition, metalenses based on arbitrary polarization at various working wavelength are also demonstrated, showing that the method has powerful design ability. Various optical properties of nanostructures, such as phase shift and polarization, are manipulated by deep neural networks, which can greatly promote the development of multifunctional devices and further pave the way for optical display, communication, computing, sensing, and other applications.

Long‐Lived Liquid Marbles for Green Applications

AbstractLiquid marbles allow for quantities of various liquids to be encapsulated by hydrophobic particles, thus ensuring isolation from the external environment. The unique properties provided by this soft solid has allowed for use in a wide array of different applications. Liquid marbles do however have certain drawbacks, with lifetime and robustness often being limited. Within this review, particle characteristics that impact liquid marble stability are critically discussed, in addition to other factors, such as internal and external environments, that can be engineered to achieve a robust long‐lived liquid marble. New emerging applications, which will benefit from this improvement, are explored such as unconventional computing, cell mimicry, and soft lithography. Incorporation of liquid marbles and liquid crystal technologies shows promise in utilizing structural color for optical display applications, and within green and environmental applications, liquid marble technology is increasingly adapted for use in energy conversion, heavy metal recovery, CO2 capture, and oil removal.

Synthesis and luminescent properties of Ba3Y3.88Gd0.12O9:Eu3+ phosphors with enhanced red emission

In this work, the Gd3+/Eu3+ activated Ba3Y4O9 (BYO) phosphors were successfully synthesized via coprecipitation method at 1400 °C. The precursor composition, crystal structure stability, microscopic morphology, photoluminescence (PL)/photoluminescence excitation (PLE) spectra and fluorescence attenuation analysis of the phosphors are discussed in detail. The chemical composition of the precursor was determined by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetry (TG) analysis; According to field emission-scanning electron microscopy (FE-SEM) analysis, it is found that the particle size of phosphor is uniform and the agglomeration is few. According to PL/PLE spectra analysis, Ba3Y3.28Eu0.6Gd0.12O9 phosphors has the strongest excitation band at 260 nm and the strongest emission band at 614 nm, and the fluorescence intensity of Ba3Y3.28Eu0.6Gd0.12O9 is higher than that of Ba3Y3.4Eu0.6O9. The quenching concentration of Eu3+ in Ba3Y3.88–4xEu4xGd0.12O9 phosphors is x = 0.15 and the mechanism of quenching concentration of Eu3+ is electric dipole-quadrupole type interactions. The lifetime value of Ba3Y3.88–4xEu4xGd0.12O9 (x = 0.15) phosphors is 0.686 ms and decreases with the increase of Eu3+ content. In addition, the CIE chromaticity diagram of Ba3Y3.28Eu0.6Gd0.12O9 phosphors is (0.66, 0.34). Finally, the lamp beads assembled with Ba3Y3.28Eu0.6Gd0.12O9 phosphors have an ideal luminous effect. Therefore, the Ba3Y3.88–4xEu4xGd0.12O9 phosphors designed in this work may hopefully meet the requirements of various lighting and optical display applications.

Structural and optical studies of cerium doped gadolinium oxide phosphor

This research aims to study the influence of variation of doping concentration on various properties of Ce3+ doped Gd2O3 phosphor. The phosphors (Gd1−xCex)2O3 (0 ≤ x ≤ 0.15) were successfully synthesized by the solution combustion method. The structural and optical properties of the prepared phosphors were studied. Rietveld refinement confirms the formation of the cubic phase. Fourier transform infrared spectra further confirm the formation of the phosphor. It is found that an enhancement in doping concentration of Ce3+ results in the expansion of the crystal lattice, leading to a reduction in crystallite size as well as in the optical band gap. Photoluminescence emission spectra are studied, and the exact emission colour is confirmed using 1931 Commission Internationale de l’Eclairage (CIE) chromaticity coordinates. The prepared phosphor exhibits bluish green emission corresponding to 5d–4f transitions of the trivalent cerium ion and can be used as a promising candidate in optical display applications and LED applications.

Luminescence of rare earth doped ZnS nanophosphors for the applications in optical displays

Abstract Semiconductor phosphors activated with rare earth ions form a good luminescent material for optical display applications. The emission properties of Ce3+ and Eu3+ ions doped ZnS synthesized by solid state reaction method were discussed in the present paper. The structural, optical and morphological properties of these materials were characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Field Emission scanning electron microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), UV–Vis Spectroscopy and Photoluminescence (PL) measurements. The XRD results showed that the synthesized materials have hexagonal wurtzite structure. The presence of vibrational bonds corresponding to various functional groups was identified by FTIR spectroscopy. The absorption edge and the band gap energy were calculated using UV–Vis Spectroscopy and the purity of the materials were confirmed using EDS spectroscopy. The photoluminescence results of rare earth doped materials indicate that their emission characteristics of radiative transitions are around the 3+ state of electronic energy states of these atoms. The CIE coordinates of these materials were calculated and the results suggested that ZnS: Ce3+ and ZnS: Eu3+ can be used for optical display applications.

Reflectance-tunable terahertz polarization reflector using indium tin oxide

Indium tin oxide (ITO) is a transparent conductive material that is widely used in optical display applications and terahertz (THz) devices. This paper proposes an ITO-based THz polarization reflector. The proposed reflector is based on the wire-grid ITO pattern and glass substrate, with tunable THz reflectance, high optical transparency, and excellent stability. The performance of the proposed reflector is demonstrated and validated through experiments using a CW THz system and a UV–Vis spectrometer. The experimental results are in good agreement with the numerical simulation. The proposed reflector has a tunable THz reflectance from 0.5 to 0.97 in the THz frequency range (0.22–0.5 THz) and a high optical transmittance of approximately 60% in the wavelength range 450–800 nm. The proposed device successfully optimizes the radiation path in THz and optical hybrid systems to significantly improve the system performance. The work presented in this paper provides a new method for designing THz devices based on transparent conductive materials.

Structural and spectroscopic investigations on Eu3+ ions doped boro-phosphate glasses for optical display applications

Eu3+ ions incorporated Boro-phosphate glasses 51H3BO3+10ZnO+20Li2Co3+9SrCo3+ (10−x)H6NO4P + xEu2O3 (where x = 0.1,0.25,0.5,1,2 and 3 in mol%) containing alkali, alkaline and heavy metals were prepared by melt quenching technique. The structural and optical behavior has been studied employing X ray diffraction, FTIR, UV–Vis-IR absorption, emission and decay spectral data. FT infrared investigations probe the availability of fundamental stretching vibrational groups in the present glasses. The phonon side band observed pertaining to the larger energy part of the 7F0→5D2 transition is ascribed to the link between coordination ions and Eu3+ions. The Judd-Ofelt (JO) parameters obtained from the emission spectra are utilized to determine the radiative parameters for the 5D0→7FJ=1,2,3 and 4 bands pertaining to the Eu3+ ions. The increasing Ω2 and the larger R values certify the higher asymmetry of the Eu3+ ions site and Eu–O covalency. The experimental lifetime pertaining to the 5D0 excited level of the Eu3+ ions in the titled glasses have been investigated through decay curve analysis. Emission intensities characterized through the CIE diagram and (x = 0.617, y = 0.323) color coordinates suggests that acute red emission exhibited by the titled glasses are appropriate for lighting applications and display devices.

Multilevel reflectance switching of ultrathin phase-change films

Several design techniques for engineering the visible optical and near-infrared response of a thin film are explored. These designs require optically active and absorbing materials and should be easily grown on a large scale. Switchable chalcogenide phase-change material heterostructures with three active layers are grown here using pulsed laser deposition. Both Fabry–Perot and strong interference principles are explored to tune the reflectance. Robust multilevel switching is demonstrated for both principles using dynamic ellipsometry, and measured reflectance profiles agree well with simulations. We find, however, that switching the bottom layer of a three-layer device does not yield a significant change in reflectance, indicating a maximum in accessible levels. The pulsed laser deposition films grown show promise for optical display applications, with three shown reflectance levels.

In Situ Doping System To Improve the Electric-Field-Induced Fluorescence Properties of CdZnS/ZnS Quantum Rods for Light-Emitting Devices

One-dimensional quantum rods (QRs) have the properties of the electron and hole are separated under the electric field, the overlap of the wave function decreases, and photoluminescence quenching occurs. Because of these properties, QRs can be used in optical switching and future display applications. The CdZnS/ZnS QR is a material capable of emitting blue light. CdZnS/ZnS can easily separate carriers because the difference between the valence band of the core and the shell is small. However, CdS and ZnS have very low hole conductivity and cannot easily be separated. To solve this problem, we developed an in situ doping system and demonstrated nitrogen doping. The in situ doping system not only coats ZnS onto CdZnS QR but also proceeds with nitrogen doping. Previously studied doping methods additionally doped the synthesized nanomaterials and had no effect of doping because the dopant was not dispersed without subsequent heat treatment. However, the in situ doping system grows the ZnS shell and uniformly ...

Warm white light emission of apatite-type compound Ca4Y6O(SiO4)6 doped with Dy3+

A series of Ca4Y6O(SiO4)6: x%Dy3+ (x = 1, 3, 5, 7, 9) phosphors were synthesized successfully via a conventional solid-state method at high temperature. The X-ray diffraction results show that all obtained samples are the pure hexagonal crystal structure of the space group P63/m (No.176). The blue (4F9/2 → 6H15/2) and yellow (4F9/2 → 6H13/2) emissions of Ca4Y6O(SiO4)6:7% Dy3+ phosphors are of such a ratio to produce almost perfect white light with CIE coordinates of (0.330, 0.339). The correlated color temperature is about 5600 K, close to that of the midday sunlight (5500 K). In addition, both the emission intensity and the CIE coordinates exhibit an excellent thermal stability in the temperature range of RT ∼ 300 °C. Our study illustrates that Ca4Y6O(SiO4)6:7%Dy3+ may serve as potential warm white lighting phosphors in NUV-based solid state lighting and optical display applications.

Controlling the morphology and size of (Gd0.98−xTb0.02Eu x )2O3 phosphors presenting tunable emission: formation process and luminescent properties

The (Gd0.98−xTb0.02Eu x )2O3 phosphors have been successfully obtained using the urea-based homogeneous precipitation method in the present work. The particle growth of the precursors with mono-dispersion spherical morphology is surface-diffusion controlled and precipitated in the order of the Tb(OH)CO3 > Gd(OH)CO3 > Eu(OH)CO3, and the formation process has been also studied in detail. Partially replacing the pure water with ethylene glycol (EG) can control the particle size and morphology owing to its lower permittivity constant and interface energy. By monitoring the excitation at 314 nm (4f8 → 4f75d1 transition of Tb3+), the (Gd0.98−xTb0.02Eu x )2O3 phosphors exhibit both Tb3+ (green) and Eu3+ (red) emissions at 547 and 613 nm, respectively. The presence of Gd3+ and Tb3+ excitation bands on the PLE spectra by monitoring the Eu3+ emission directly provides an evidence of the Tb3+ → Eu3+ and Gd3+ → Eu3+ energy transfer, respectively. The quenching concentration is determined to be 2.0 at.%, and the quenching mechanism is determined to be the exchange reaction between Eu3+. The emission color can be readily tuned from approximately green to red via adjusting the Eu3+ content. The temperature-dependent analysis has been performed, and the results indicate that the (Gd0.98−xTb0.02Eu x )2O3 samples possess good thermal stability. Owing to the Tb3+ → Eu3+ energy transfer, the lifetime for the Tb3+ emission rapidly decreases, and the energy transfer efficiency has been calculated. The EG addition does not bring appreciable changes to the lifetime values for the both Tb3+ and Eu3+ emissions, but enhances remarkably the luminescent intensity which confirms the variation of the particle morphology/size, and the reason can be explained by the scattering of the light. The (Gd0.98−xTb0.02Eu x )2O3 phosphors developed in this work hopefully meet the requirements of various lighting and optical display applications.

Eu3+ doped self-activated Ca8ZrMg(PO4)6(SiO4) phosphor with tunable luminescence properties

Abstract: Single-host white-light emission phosphors stand a good chance to serve in the next-generation high-power white light emitting diodes. Eu3+-doped self-activated Ca8ZrMg(PO4)6(SiO4) phosphor was synthesized by a high temperature solid-state reaction which can realize white light emission by tuning spectrum. The analysis of XRD, SEM, UV–vis DRS, luminescent spectra, and emission dynamic curves were applied to investigate the obtained samples. Upon 295 nm excitation, the Ca8ZrMg(PO4)6(SiO4): Eu3+ phosphors contain two dominating bands peaked at 470 and 615 nm, which are attributed to the charge transfer (CT) transition from Zr4+ to O2− and the characteristic transition 5D0→7F2 of the Eu3+ ions, respectively. In view of the energy transfer between Zr-O CT and Eu3+ ions, the chromaticity coordinates of Ca8ZrMg(PO4)6(SiO4): Eu3+ phosphors can be tuned from (0.2186, 0.2858) to (0.5413, 0.3295). Present work indicates that the novel Ca8ZrMg(PO4)6(SiO4) is a promising candidate as a single-host white phosphor with an excellent thermal stability for optical display applications.

Ca9Na1/3M2(1-x)/3(PO4)7:2x/3Eu3+ (M = Gd, Y): A promising red-emitting phosphor without concentration quenching for optical display applications

Zero-quenching red-emitting phosphors Ca9Na1/3M2(1-x)/3(PO4)7:2x/3Eu3+ (M = Gd, Y) were successfully synthesized by solid-state method. The analysis of XRD, SEM, UV–vis DRS, luminescent spectra, and the emission dynamics curves were applied to investigate the obtained powders. These results showed that Eu3+-activated Ca9Na1/3M2(1-x)/3(PO4)7 (M = Gd, Y) phosphors can absorb the wavelength from 220 to 480nm, which is matched well with commercial near-UV chips, and emit intense red light without concentration quenching. Notably, the integral intensities calculated from Ca9Na1/3Gd2(1-x)/3(PO4)7:2x/3 Eu3+ and Ca9Na1/3Y2(1-x)/3(PO4)7:2x/3Eu3+ phosphors were about 3.05 and 2.64 times higher than that of commercial phosphor Y2O3:Eu3+, respectively. In addition, the CIE color coordinate was calculated to be (0.65, 0.34). It should be pointed out that the FWHM of 5D0→7F2 transition band was greatly expanded due to the presence of multi-sites for Eu3+ ions in the hosts. These results suggest that the obtained phosphors have the potential for lighting and optical display applications.