Hak-Sung Jung

Quantitative analysis and efficient surface modification of silica nanoparticles

Aminofunctional trialkoxysilanes such as aminopropyltrimethoxysilane (APTMS) and (3-trimethoxysilylpropyl)diethylenetriamine (DETAS) were employed as a surface modification molecule for generating monolayer modification on the surface of silica (SiO2) nanoparticles. We were able to quantitatively analyze the number of amine functional groups on the modified SiO2 nanoparticles by acid-base back titrationmethod and determine the effective number of amine functional groups for the successive chemical reaction by absorption measurements after treating with fluorescent rhodamine B isothiocyanate (RITC) molecules. The numbers of amine sites measured by back titration were 2.7 and 7.7 ea/nm2 for SiO2-APTMS and SiO2-DETAS, respectively, while the numbers of effective amine sites measured by absorption calibration were about one fifth of the total amine sites, namely, 0.44 and 1.3 ea/nm2 for SiO2-APTMS(RITC) and SiO2-DETAS(RITC), respectively. Furthermore, it was confirmed that the reactivity of amino groups on the surface-modified silica nanoparticles could be maintained in ethanol for more than 1.5 months without showing any significant differences in the reactivity.

Rapid Imaging of Latent Fingerprints Using Biocompatible Fluorescent Silica Nanoparticles

Fluorescent silica nanoparticles (FSNPs) are synthesized through the Stöber method by incorporating silane-modified organic dye molecules. The modified fluorescent organic dye molecule is able to be prepared by allylation and hydrosilylation reactions. The optical properties of as-prepared FSNPs are shown the similar optical properties of PR254A (allylated Pigment Red 254) and have outstanding photostability. The polyvinylpyrrolidone (PVP) is introduced onto the surface of FSNP to enhance the binding affinity of PVP-coated FSNP for latent fingerprints (LFPs) detection. The simple preparation and easy control of surface properties of FSNPs show potential as a fluorescent labeling material for enhanced latent fingerprint detection on hydrophilic and hydrophobic substrates in forensic science for individual identification.

White light-emitting diodes using thermally and photochemically stable fluorescent silica nanoparticles as color-converters

Trialkoxysilyl terminal groups were directly introduced into fluorescent organic dye molecules by consecutive allylation and hydrosilation reactions; the derivatized dye molecules were then successfully embedded into silica nanoparticles by the Stober method. Those fluorescent silica nanoparticles (FSNPs) had emission colors corresponding to each fluorescent organic dye used (yellowish-green and red) and showed excellent thermal and photochemical stabilities. A white light-emitting diode (WLED) was fabricated by combining the FSNP/silicone encapsulant composite incorporated with FSNPs having yellowish-green and red emission with a blue InGaN LED (BLED). The resulting three-color RGB FSNP-LED exhibited a good color rendering index (CRI), Ra 86.7, at the correlated color temperature of 5452.6 K and CIE coordinates of (0.3334, 0.3360), indicating that the combination of highly fluorescent silica nanoparticles with LEDs can offer a promising solution for white light sources with high color rendering properties.

Silica-coated gradient alloy quantum dots with high luminescence for converter materials in white light-emitting diodes

Hydrophobic gradient alloy quantum dots (QDs) were prepared through a facile organic route. The amphiphilic, non-ionic polymer (PVP) was absorbed onto the surface of QDs, and therefore, the PVP coated QD (QD@PVP) could be dispersible in both polar and non-polar solvents. The QD@PVP was dispersed in ethanol and tetraethyl orthosilicate (TEOS) was added with a basic catalyst in order to generate silica shell encapsulated QDs (QD@SiO2). We report a preparation method for QD@SiO2 that maintains their high luminescence and thermal- and photo-stability using dimethylamine (DMA) as a basic catalyst. White light-emitting-diodes (WLEDs) incorporating the QD@SiO2 exhibited good performance in terms of superior luminescence efficiency and high color purity.

Surface Coating of Gradient Alloy Quantum Dots with Oxide Layer in White-Light-Emitting Diodes for Display Backlights

Recently, quantum dots (QDs) have been successfully developed as efficient color converters for light-emitting diodes (LEDs) display due to excellent optical properties of QDs. Herein, we demonstrate a new approach to form metal oxide layers (or metal oxide coating) on the exterior surface of gradient alloy QDs (the most advanced chemical architecture QDs developed thus far wherein the lattice parameter from the core to shell is changing in a gradient fashion) in order to improve the photochemical stability and photoluminescence efficiency. The resulting CdO-treated QDs are incorporated into polymer matrix films to fabricate a backlight unit as a part of display panel wherein CdO-treated gradient alloy QDs are utilized as color converters upon the blue-LED excitation. The fabricated 9.7 in. iPad 2 tablet liquid crystal display panel exhibited an excellent uniformity in terms of CIE chromaticity, luminance, and bright variation and superb durability test results (maintenance of ca. 110% brightness compared to initial value even after 3 weeks of operation).