Trung-Kien Nguyen-Duc

Hanoi University of Science and Technology · Advanced Institute for Science and Technology

Calcium titanate (CaTiO3), a multi-metal oxide has received extensive attention in recent years, due to its unique structural features, high chemical stability, strong catalytic activity, inexpensiveness, low toxicity, and easy synthesis. In this work, we have focused our research on and investigated the influence of Ca weight on the microstructure...

Phosphor-converted white light-emitting diodes (WLEDs) have received significant attention; however, the leaked light from their blue InGaN chips has an undesirable effect on human health. Hence, it is necessary to develop red, green, and blue-emitting phosphors, which can be excited by an NUV chip instead of a blue chip. Herein, green-emitting ZnO...

Eu³⁺-doped phosphors have been much attractive owing to their narrow-band red emission peak at 610–630 nm with high color purity; however, the weak and narrow absorption band in the NUV region limits their applications. Doping a higher amount of Eu³⁺ ions into a non-concentration quenching host could be key to enhancing the efficiency of the absorp...

In this report, SYGO:Eu3+ red phosphor have been successfully synthesized by sol-gel method. The X-ray diffraction results show that the sample has a cubic crystal structure, belonging to the space group Ia3d (230) without any doping. Scanning electron microscopy (FE-SEM) combined with EDS was performed to determine the microstructure and elemental...

We study phase transition properties of the two-dimensional q-state clock model by an extensive Monte Carlo simulation. By analyzing the Binder ratio and its temperature derivative, we confirm that the two-dimensional q-state clock model exhibits two distinct Kosterlitz-Thouless phase transitions for q=5,6 but it has one second-order phase transiti...

This work reports an excellent quantum efficiency and superior color purity CaAl12O19-CaAl4O7-MgAl2O4:Mn4+ (CCM:Mn4+) red-emitting phosphor. This phosphor can be excited by a broad excitation band ranging from 300 to 500 nm, and it generates an intense broadband red emission peaking at 656 nm. The CCM:0.5%Mn4+ phosphor-possessed superior color puri...

Mô hình hai chiều (2D) XY thông thường có xuất hiện chuyển pha bậc vô hạn hay còn gọi là chuyển pha Kosterlitz-Thouless (KT). Tuy nhiên, các vật liệu thực tế thì ngoài tương tác trao đổi còn có thêm vai trò của trường tinh thể. Do vậy, mô hình tổng quát 2D XYh4 là mô hình XY có thêm trường tinh thể bất đẳng hướng h4 có triển vọng mô tả các vật liệu...

Preparation and characteristic of Nanorod‐like Zn2GeO4 doped with Eu3+ or ZGO:xEu3+ (x = 0 ÷ 0.05) which synthesized via the hydrothermal method are described. The influence of Eu3+ doping ions on the structure and the optical properties of ZGO was also investigated. According to the PL spectra, ZGO:xEu3+ nanophosphors gave a red emission due to th...

Heterostructure alloys with controlled structure and composition are essential for future electronics and optoelectronics. While heterostructure formation creates sharp electronic junction, alloying allows bandgap tunability. Herein, ZnS/ZnO heterostructure-alloy hexagonal micropyramids are grown on Si/SiO2 wafers for the first time by facile therm...

This paper reports the first attempt to synthesize un-doped spherical Zn2GeO4 stoichiometry and Mn²⁺ doped Zn2GeO4 nanoparticles to achieve a controlled luminescence, particularly, by changing Zn:Ge ratio and Mn²⁺ concentration during the hydrothermal process. The morphology of the un-doped Zn2GeO4 nanoparticle was depended on the Zn:Ge ratio that...

A series of Mn2+ doped zinc germinate ZGO:xMn2+ (x = 0-0.05) nanorods were synthesized successfully by the hydrothermal method. X-ray diffraction, Rietveld refinement were used to describe the structural information of the ZGO:xMn2+ nanocrystals. XRD revealed that crystal phases of the ZGO:xMn2+ is rhombohedral and in the R-3 space group. The unit...

Zn2GeO4 (ZGO) phosphor and Mn-doped ZGO (ZGO:Mn2+) phosphor were successfully synthesized through co-precipitation. Results indicated that Zn ions were successfully replaced by Mn ions, and Mn doping led to a lattice contraction. Under UV light excitation, the undoped ZGO exhibited a strong white-bluish emission at 517 nm and weak green emission at...

This paper reports the red visible luminescence of ZnO nanofibers synthesized by electrospinning followed by thermal annealing. The ZnO nanofibers were prepared by electrospinning of the precursor mixture of zinc acetate/polyvinylpyrrolidone (PVP) by using different PVP concentrations, while thermal annealing was kept at 600oC. The ZnO nanofiber di...

Light Emitting Diodes (LED) shows an important role in replacing traditional lamps due to their longevity, high efficiency, and environment-friendly operation. However, a large portion of the electricity applied on LED converts to heat, raising up the p-n junction working temperature, and lowering the output-light quality and the LED lifetime as we...

Single-phase far-red-emitting ZnAl2O4:Cr3+ phosphor has been successfully synthesized by a sol-gel method. The phosphor can be well excited by NUV, violet, and green lights, and it strongly emits multi-peak broadband emissions in the far-red region peaking at 687 and 698 nm, matching well with the absorption band of phytochrome. The maximum PL inte...

This article reports on the synthesis procedure of ZnO nanoparticles/nanofibers structure by electrospinning method using Zinc acetate and polyvinylpyrrolidone (PVP) surfactant as reagents and evaluates their luminescent properties. The microstructure of ZnO nanoparticles/nanofibers was observed by FE-SEM. The phase formation of ZnO nanoparticles/n...

Chúng tôi nghiên cứu hiện tượng chuyển pha của mô hình q-state clock hai chiều bằng phương pháp mô phỏng Monte Carlo. Chúng tôi tính toán các đại lượng vật lý như là: nhiệt dung riêng, độ từ hoá và mô đun xoắn cho q > 5 (cụ thể q = 6 và 8). Nhiệt dung riêng và độ từ hóa chỉ ra mô hình có hai chuyển pha, bao gồm chuyển pha trên, T2, giữa pha mất trậ...

Deep-red-emitting CaYAlO4:Cr3+ phosphors were synthesized by the sol–gel method followed by heat treatment. The effects of sintering temperature on the phase structure, morphology, and luminescence properties of the phosphors were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy, Raman scattering spectroscopy, en...

In an arbitrary system subjected to a quench, or an external field that varies the system parameters, the degrees of freedom increases double in comparison to that of an isolated system. In this study, we consider the quantum impurity system subjected to a quench, and measure the corresponding time-evolution of the spectral function, which is origi...

In this work, MgAl2O4:Cr³⁺ phosphor has been synthesized by the co-precipitation approach coupled with heat treatment. The phase structure, morphology, composition and luminescent properties of the phosphor were investigated in detail by x-ray diffraction, field emission-scanning electron microscopy, energy dispersive x-ray spectroscopy and steady-...

Blue/red emitting bi-phase Eu³⁺/Eu²⁺-doped SrPCl-based phosphors were synthesized using a co-precipitation method followed by sintering process in air ambient and in reducing gas. The effect of sintering/reducing temperature and Eu concentration on the structure, morphology and luminescent spectra were investigated. XRD patterns analysis showed tha...

The measurements of the magnetic and nematic correlation lengths in a generalization of the two dimensional XY model on the square lattice are presented using classical Monte Carlo simulation. The full phase diagram is re-examined based on these correlation lengths, demonstrating their power in studying generalized XY models. The ratio between the...

This work presents a simple and effective technique to decrease the driver temperature by filling the potting materials into space between driver and the interior wall of a LED bulb's heatsink.The thermal exchange between the LED bulb, including LEDchips, driver, heatsink, potting materials and the ambient were studied using the finite element meth...

This paper reports a novel way for the synthesis of a europium (Eu)-doped fluor-hydroxyapatite (FHA) nanostructure to control the luminescence of hydroxyapatite nanophosphor, particularly, by applying optimum fluorine concentrations, annealed temperatures and pH value. The Eu-doped FHA was made using the co-precipitation method followed by thermal...

K- feldspars in pegmatites from Luc Yen gem mining area, Yen Bai province, Vietnam were studied by XRF, XRD and Raman spectroscopy. Chemical analysis determined the K-Feldspars in the form of (K0.8909Na0.0388Ca0.002Pb0.0042Cs0.0024Rb0.0338)(Al0.9975Fe0.0053Ti0.0004)Si2.988O8. Both XRD and Raman spectroscopy indicated Luc Yen K-feldspars as orthocla...

Room-temperature ferromagnetism of diluted magnetic semiconductors (DMSs) doped with light elements has been extensively investigated for potential applications in spintronic devices. Indeed, the mechanism underlying ferromagnetism in DMSs of low concentrations has been studied from both theoretical and experimental perspectives. Theoretically, fir...

This paper reports the first attempt to characterize the light-emission from Ge/GeO2 nanostructure synthesized by thermal evaporation. The synthesized Ge/GeO2 was observed to have a nanowire structure. Photoluminescence (PL) results show that the emission center of the PL peak at about 410 and 485 nm depends on the excitation wavelength. Experiment...

In this study, ZnO nanostructures were synthesized on SiO2/Si substrate by thermal evaporation method. The dependence of the crystalline phase, morphologies and chemical composition of the samples grown at different substrate temperatures were systematically studied. The XRD, Raman spectra, FTIR spectra and XPS results reveal the existence of Zn2Si...

The Eu3+ and Eu2+-doped SrBP phosphor powders were synthesized via the co-precipitation method and subsequent reduction of the dopants in N2/H2 gas for application in white light-emitting devices (WLED). The as-prepared powders were annealed at a temperature range of 600°C to 1300°C in air ambient to form Eu3+-doped phosphors with an average partic...

More than 300 natural and synthetic emeralds from various sources were examined with Raman spectroscopy. Of this set, 36 KBr pellets of different samples were also examined with FTIR spectroscopy. In many cases, the presence or absence of specific Raman and FTIR bands, and the exact position of apparent maxima, are correlated to the weight percenta...

The room-temperature ferromagnetism of diluted magnetic semiconductors (DMS) doped with light elements has been extensively studied for potential applications in spintronic devices. The existence and stability of ferromagnetism of DMS with low concentration regime is an interesting topic, followed by researches using both Monte Carlo (MC) simulatio...

ZnS nanoparticles were synthesized by hydrothermal and co-precipitation methods. The starting precursors were sodium thiosulfate and zinc chloride for the hydrothermal method; zinc acetate dihydrate and sodium polyphosphate for the co-precipitation method. Scanning electron microscopy (SEM) images of ZnS powder prepared by hydrothermal route show t...

Silicon nanowires (NWs) and vertical nanowire-based Si/Ge heterostructures are expected to be building blocks for future devices, e.g. field-effect transistors or thermoelectric elements. In principle two approaches can be applied to synthesise these NWs: the ‘bottom-up’ and the ‘top-down’ approach. The most common method for the former is the vapo...

An effective and low-cost method to fabricate hexagonally patterned, vertically aligned Si/Ge superlattice nanowires with diameters below 20 nm is presented. By combining the growth of Si/Ge superlattices by molecular beam epitaxy, prepatterning the substrate by anodic aluminum oxide masks, and finally metal-assisted chemical wet etching, this meth...

Vertical epitaxial short (200-300 nm long) silicon nanowires (Si NWs) grown by molecular beam epitaxy on Si(111) substrates were separately doped p- and n-type ex situ by implanting with B, P and As ions respectively at room temperature. Multi-energy implantations were used for each case, with fluences of the order of 10(13)-10(14) cm(-2), and the...

The kinetic formation of self-assembled Ge/Si hut clusters grown by ultra-high vacuum chemical-vapor deposition has been investigated by means of reflection high-energy electron diffraction, atomic force microscopy and photoluminescence spectroscopy. We show that point defects that are induced in the epilayers grown at substrate temperatures below...

The kinetic formation of self-assembled Ge/Si hut clusters grown by ultra-high vacuum chemical-vapour deposition has been investigated by means of reflection high-energy electron diffraction, atomic force microscopy and photoluminescence spectroscopy. We show that point defects that are induced in the epilayers grown at substrate temperatures below...

Structural and optical characterizations via reflection high-energy electron diffraction and atomic force microscopy have been combined to investigate the kinetic formation of self-assembled Ge/Si hut clusters grown at a substrate temperature of 525 °C by ultra-high vacuum chemical-vapor deposition. It is shown that point defects that are induced i...

Structural and optical characterizations via reflection high-energy electron diffraction, atomic force microscopy and photoluminescence spectroscopy have been combined to investigate the kinetic formation of self-assembled Ge/Si hut clusters grown by ultra-high-vacuum chemical-vapor deposition. We show that point defects that are induced in the Ge...

Single and stacked layers of Ge/Si quantum dots were grown in SiO2 windows patterned by electron-beam lithography on oxidized Si (001) substrates. The growth of a silicon buffer layer prior to Ge deposition is found to be an additional parameter for adjusting the Ge-dot nucleation process. We show that the silicon buffer layer evolves towards [113]...