Rustamzhon Melikov

Fluorescent protein integrated white LEDs for displays.

The usage time of displays (e.g., TVs, mobile phones, etc) is in general shorter than their functional life time, which worsens the electronic waste (e-waste) problem around the world. The integration of biomaterials into electronics can help to reduce the e-waste problem. In this study, we demonstrate fluorescent protein integrated white LEDs to use as a backlight source for liquid crystal (LC) displays for the first time. We express and purify enhanced green fluorescent protein (eGFP) and monomeric Cherry protein (mCherry), and afterward we integrate these proteins as a wavelength-converter on a blue LED chip. The protein-integrated backlight exhibits a high luminous efficacy of 248 lm/Wopt and the area of the gamut covers 80% of the NTSC color gamut. The resultant colors and objects in the image on the display can be well observed and distinguished. Therefore, fluorescent proteins show promise for display applications.

Silk-hydrogel Lenses for Light-emitting Diodes

Today the high demand for electronics leads to massive production of waste, thus green materials based electronic devices are becoming more important for environmental protection and sustainability. The biomaterial based hydrogels are widely used in tissue engineering, but their uses in photonics are limited. In this study, silk fibroin protein in hydrogel form is explored as a bio-friendly alternative to conventional polymers for lens applications in light-emitting diodes. The concentration of silk fibroin protein and crosslinking agent had direct effects on optical properties of silk hydrogel. The spatial radiation intensity distribution was controlled via dome- and crater-type silk-hydrogel lenses. The hydrogel lens showed a light extraction efficiency over 0.95 on a warm white LED. The stability of silk hydrogel lens is enhanced approximately three-folds by using a biocompatible/biodegradable poly(ester-urethane) coating and more than three orders of magnitude by using an edible paraffin wax coating. Therefore, biomaterial lenses show promise for green optoelectronic applications.

Stokes-Shift-Engineered Indium Phosphide Quantum Dots for Efficient Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) show promise because of their potential for low-cost, large-area, and high-efficiency energy harvesting. Stokes shift engineering of luminescent quantum dots (QDs) is a favorable approach to suppress reabsorption losses in LSCs; however, the use of highly toxic heavy metals in QDs constitutes a serious concern for environmental sustainability. Here, we report LSCs based on cadmium-free InP/ZnO core/shell QDs with type-II band alignment that allow for the suppression of reabsorption by Stokes shift engineering. The spectral emission and absorption overlap was controlled by the growth of a ZnO shell on an InP core. At the same time, the ZnO layer also facilitates the photostability of the QDs within the host matrix. We analyzed the optical performance of indium-based LSCs and identified the optical efficiency as 1.45%. The transparency, flexibility, and cadmium-free content of the LSCs hold promise for solar window applications.

Structural control of InP/ZnS core/shell quantum dots enables high-quality white LEDs

Herein, we demonstrate that the structural and optical control of InP-based quantum dots (QDs) can lead to high-performance light-emitting diodes (LEDs). Zinc sulphide (ZnS) shells passivate the InP QD core and increase the quantum yield in green-emitting QDs by 13-fold and red-emitting QDs by 8-fold. The optimised QDs are integrated in the liquid state to eliminate aggregation-induced emission quenching and we fabricated white LEDs with a warm, neutral and cool-white appearance by the down-conversion mechanism. The QD-functionalized white LEDs achieve luminous efficiency (LE) up to 14.7 lm W-1 and colour-rendering index up to 80. The structural and optical control of InP/ZnS core/shell QDs enable 23-fold enhancement in LE of white LEDs compared to ones containing only QDs of InP core.

Excitonic Energy Transfer within InP/ZnS Quantum Dot Langmuir–Blodgett Assemblies

Interparticle energy transfer offers great promise to a diverse range of applications ranging from artificial solar energy harvesting to nanoscale rulers in biology. Here, we assembled InP/ZnS core/shell quantum dot monolayers via the Langmuir–Blodgett technique and studied the effect of ZnS shell thickness on the excitonic energy transfer within these core/shell quantum dots. Three types of InP-based core/shell quantum dot Langmuir–Blodgett assemblies with different ZnS shell thicknesses were assembled. The structural and optical properties of colloidal quantum dots reveal the successful multiple ZnS shell growth, and atomic force microscopy studies show the smoothness of the assembled monolayers. Time-resolved photoluminescence (PL) and fluorescence lifetime imaging microscopy (FLIM) studies of the thick-shell QD monolayer reveal narrower lifetime distribution in comparison with the thin-shell QD monolayer. The interparticle excitonic energy transfer was studied by spectrally resolved PL traces, and higher energy transfer was observed for the thin-shell InP/1ZnS QD monolayer. Finally, we calculated the average exciton energy and indicated that the energy transfer induced exciton energy shift decreased significantly from 95 to 27 meV after multiple ZnS shell growth.

Unravelling radiative energy transfer in solid-state lighting

Today, a wide variety of organic and inorganic luminescent materials (e.g., phosphors, quantum dots, etc.) are being used for lighting and new materials (e.g., graphene, perovskite, etc.) are currently under investigation. However, the understanding of radiative energy transfer is limited, even though it is critical to understand and improve the performance levels of solid-state lighting devices. In this study, we derived a matrix approach that includes absorption, reabsorption, inter-absorption and their iterative and combinatorial interactions for one and multiple types of fluorophores, which is simplified to an analytical matrix. This mathematical approach gives results that agree well with the measured spectral and efficiency characteristics of color-conversion light-emitting diodes. Moreover, it also provides a deep physical insight by uncovering the entire radiative interactions and their contribution to the output optical spectrum. The model is universal and applicable for all kinds of fluorophores.Today, a wide variety of organic and inorganic luminescent materials (e.g., phosphors, quantum dots, etc.) are being used for lighting and new materials (e.g., graphene, perovskite, etc.) are currently under investigation. However, the understanding of radiative energy transfer is limited, even though it is critical to understand and improve the performance levels of solid-state lighting devices. In this study, we derived a matrix approach that includes absorption, reabsorption, inter-absorption and their iterative and combinatorial interactions for one and multiple types of fluorophores, which is simplified to an analytical matrix. This mathematical approach gives results that agree well with the measured spectral and efficiency characteristics of color-conversion light-emitting diodes. Moreover, it also provides a deep physical insight by uncovering the entire radiative interactions and their contribution to the output optical spectrum. The model is universal and applicable for all kinds of fluorophores.

Silk-Based Aqueous Microcontact Printing

Lithography, the transfer of patterns to a film or substrate, is the basis by which many modern technological devices and components are produced. However, established lithographic approaches generally use complex techniques, expensive equipment, and advanced materials. Here, we introduce a water-based microcontact printing method using silk that is simple, inexpensive, ecofriendly, and recyclable. Whereas the traditional microcontact printing technique facilitates only negative lithography, the synergetic interaction of the silk, water, and common chemicals in our technique enables both positive and negative patterning using a single stamp. Among diverse application possibilities, we exemplify a proof of concept of the method through optimizing its metal lift-off process and demonstrate the fabrication of electromagnetic metamaterial elements on both solid and flexible substrates. The results indicate that the method demonstrated herein is universally applicable to device production and technology development.

3D coffee stains

When a liquid droplet (e.g., coffee, wine, etc.) is splattered on a surface, the droplet dries in a ring-shaped stain. This widely observed pattern in everyday life occurs due to the phenomenon known as a coffee stain (or coffee ring) effect. While the droplet dries, the capillary flow moves and deposits the particles toward the pinned edges, which shows a 2D ring-like structure. Here we demonstrate the transition from a 2D to a 3D coffee stain that has a well-defined and hollow sphere-like structure, when the substrate surface is switched from hydrophilic to superhydrophobic. The 3D stain formation starts with the evaporation of the pinned aqueous colloidal droplet placed on a superhydrophobic surface that facilitates the particle flow towards the liquid–air interface. This leads to spherical skin formation and a cavity in the droplet. Afterwards the water loss in the cavity due to pervaporation leads to bubble nucleation and growth, until complete evaporation of the solvent. In addition to the superhydrophobicity of the surface, the concentration of the solution also has a significant effect on 3D coffee stain formation. Advantageously, 3D coffee stain formation in a pendant droplet configuration enables the construction of all-protein lasers by integrating silk fibroin with fluorescent proteins. No tools, components and/or human intervention are needed after the construction process is initiated; therefore, 3D coffee-stains hold promise for building self-assembled and functional 3D constructs and devices from colloidal solutions.