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Blue-cyan Bi3+-doped Ca12Al14O33single bondCa3Al2O6 (CCAO:Bi3+) phosphors were synthesized using a solid-state reaction method. XRD analysis confirmed the replacement of larger Bi3+ ions by smaller Ca2+ ions in the CCAO crystal structure. UV–Vis absorption spectra demonstrated the coexistence of two Ca12Al14O33 and Ca3Al2O6 phases. SEM and EDS analysis revealed the absence of impurities in of CCAO:Bi3+ particles, which were sized 3 - 5 μm. PLE and PL spectra showed that the CCAO:Bi3+ phosphors emitted blue light peaking at 460 and 450 nm when excited at 284 and 312 nm, with a large full width at half maximum of 117 nm and 95 nm, respectively. The highest PL intensity was observed in the CCAO:2 %Bi3+ sample annealed at 1300 °C for 6 h. Excitation at 284 and 312 nm, resulted in emission peaks at 490 - 495 nm (linked to Bi3+ in [CaO6] or [CaO7] of CCAO crystals), and 443 nm (related to intrinsic defects). The tunable luminescence of CCAO:x%Bi3+ (x = 0 – 5.0) phosphors was achieved by adjusting the Bi3+ content, as shown in the Commission Internationale de L'Eclairage (CIE) chromaticity diagram. These results highlight the potential of CCAO:Bi3+ phosphors as blue-cyan components in white light-emitting diodes (WLEDs) based on NUV chips.

Perovskite-based materials have recently gained significant attention due to their unique properties. Herein, the deep and far-red-emitting LaAlO3–Al2O3:Cr3+ perovskite-based phosphors with particle sizes of 2–5 μm have been reported for the first time, demonstrating excellent responsiveness to far-red phytochrome. The synthesized phosphors exhibited a sharply defined deep and far-red emission, peaking at 735 nm, and significant absorptions in the violet (∼410 nm) and green (∼565 nm) regions. The distinct lines at 735 nm can be attributed to the robust crystal field effect of surrounding Cr3+ ions, wherein the 3+ oxidation state substitutes smaller-sized Al3+ ions in the [AlO6] octahedral site of the LaAlO3–Al2O3 lattice. The optimized LaAlO3–Al2O3:0.6%Cr3+ phosphor, annealed at 1400 °C, demonstrated exceptional characteristics, including a color purity of 100 %, a prolonged lifetime of 32.26 ms, a high activation energy of 0.501 eV, and an impressive internal quantum efficiency of 68.1 %. Moreover, a prototype of a violet-pumped LaAlO3–Al2O3:0.6%Cr3+ phosphor-coated LED showcased a well-matched emission spectrum with the absorption spectrum of far-red phytochrome, underscoring its significant potential for applications in LED-based plant growth systems.

In this study, a novel red-emitting Mn4+ doped Li2MgSn2O6 (Li2MgSn2O6:Mn4+) phosphors were successfully synthesized using a simple solid-state reaction method. XRD patterns indicated the replacement of Mn4+ ions with Sn4+ ions in the [SnO6] octahedrons site of the Li2MgSn2O6 lattice, and XPS spectra confirmed the Mn4+ oxidation state. Excited at 323 nm and 480 nm, the phosphors exhibited a strong red emission band peaking at 659 nm, attributed to the 2E → 4A2 transition of Mn4+ ions. Notably, the highest PL intensity was found in the Li2MgSn2O6:0.3%Mn4+ sample annealed at 1000 °C. These phosphors, with a particle size of 1.0 μm, possess a long lifetime of 0.176 ms, high activation energy of 0.335 eV, excellent color purity of 99.9%, and good internal and external quantum efficiency of 44.5% and 24.1%, respectively. Furthermore, an LED coated with Li2MgSn2O6:0.3%Mn4+ phosphor on a 365 nm NUV LED chip showed strong emission matching the absorption spectrum of the red phytochrome. Therefore, these results indicated that the synthesized Li2MgSn2O6:Mn4+ phosphors could be used as red-emitting materials for plant growth LED applications.

ZnS nanostructures possess exceptional features, making them highly promising as gain media and optical waveguides for nanolasers and optoelectronic devices. These features include low lasing thresholds and effortless fabrication. In this study, we present high-crystalline ZnS nanowires (NWs) and nanobelts (NBs) synthesized by using a thermal evaporation route. The remarkably low lasing thresholds of 45.3–45.5 W/cm2 are achieved at room temperature, marking a two-orders-of-magnitude improvement over reported values for ZnS nanostructures. Comprehensive analysis, incorporating techniques such as x-ray diffraction, Raman spectra, transmission electron microscopy, x-ray photoelectron spectroscopy, and photoluminescence, confirms the great quality of the synthesized nanostructures. The excitonic lasing emissions from ZnS NWs and NBs exhibit small full width at half maximum values of 5.9 and 0.53 nm, respectively. These emissions occur within cavities measuring ∼5.1 to 5.6 μm, with high-quality factors (112.6 for ZnS NWs and 598.6 for ZnS NBs), further highlighting the excellent performance of the materials. Moreover, the gain factors of 17.32–26.63 underscore the significant potential of ZnS NWs and NBs as prime candidates for ultraviolet photonic devices

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 absorption value and emission intensity. Hence, the design of Eu3+-heavily doped phosphors with a suitable host lattice is key for applications. In this study, red-emitting Eu3+-doped Gd(BO2)3-Y3BO6-GdBO3 (GdYGd:Eu3+) phosphor with a high quantum efficiency of 58.4% and excellent color purity of 99.5% is reported for the first time. The phosphor is efficiently excited by NUV light at 394 nm and emits a strong red emission band in the 590–710 nm range, peaking at 612 nm. The optimal annealing temperature and Eu3+ doping content to obtain the strongest PL intensity are 1100 °C and 20 mol%, respectively. The optimized GdYGd:Eu3+ phosphor possesses a high activation energy of 0.319 eV and a lifetime of 1.14 ms. An illustration of phosphor-coated NUV LED with chromaticity coordinates (x = 0.5636,y = 0.2961) was successfully synthesized, demonstrating the great potential of GdYGd:Eu3+ phosphor for NUV-pumped WLED applications.

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:Cu2+ phosphors have been successfully synthesized by a simple and facile thermal diffusion method. The obtained powder shows a broad emission band peaking at 525 nm and a strong absorption peak at 377 nm. The ZnO:5%Cu2+ phosphor annealed at 800 °C in 2 hours revealed a lifetime of 0.57 ms, an activation energy of 0.212 eV, and the highest emission intensity with (x, y) CIE colour coordinates (0.3130, 0.5253). A WLED prototype has been fabricated by coating the ZnO:5%Cu2+ phosphor on an NUV 375 nm LED chip, where this coated phosphor shows a high quantum efficiency (QE) of 56.6%. This is, so far, the highest reported QE value for ZnO-based phosphors. These results suggest that the ZnO:Cu2+ phosphor could be an excellent candidate for NUV-pumped phosphor-converted WLED applications.

Single-phase far-red-emitting CaAl12O19:x%Cr3+ (x = 0.1 – 3.0 mol%) phosphors were successfully synthesized by a sol-gel method. Besides a small absorption peak at 263 nm, the phosphors have two broad excitation bands in the UV-blue (350 – 475 nm) and green-red (500 – 600 nm) regions, centered at 414 and 573 nm, respectively. They give a broad emission band in the 650 – 800 nm range and several narrow emission peaks at 665, 688, 695, 700, and 709 nm under violet (414 nm) and orange (573 nm) excitations. The optimum annealing temperature and doping concentration of Cr3+ ions are 1500 °C and 0.3%, respectively. Further, the optimized CAO: 0.3%Cr3+ phosphor exhibits an excellent color purity of 100%, activation energy of 0.4 eV, a long lifetime of 4.2 ms, and good quantum efficiency of 46.2%. A prototype of plant growth LED with the CIE coordinate of (x = 0.3050; y = 0.1264) was fabricated by coating CaAl12O19:0.3%Cr3+ phosphor on a violet (410 nm) LED chip. The obtained EL spectrum of plant growth LED is well-matched with the far red phytochrome (PFr) absorption spectra, demonstrating that CaAl12O19:Cr3+ is a potential far-red-emitting phosphor for violet-pumped plant growth LEDs.

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 purity of 100%, a long lifetime of 0.49 ms, and high activation energy of 0.286 eV. Four different prototypes of plant growth light-emitting diodes (LEDs) with high quantum efficiencies of 81.8, 72.1, 67.2, and 61.1% were fabricated by coating the optimized CCM:0.5%Mn4+ phosphors onto UV (365 nm), NUV (395 nm), violet (410), and blue (460 nm) LED chips, respectively. The 81.8% and 72.1% QE values are the highest values reported for the 365 nm UV-pumped and 395 nm NUV-pumped LEDs based on Mn4+-doped oxide phosphors. Furthermore, a white LED with a high color rendering index (CRI) of 90, correlated color temperature (CCT) of 2416 K, and luminous efficacy of radiation (LER) of 216 lm/W was realized using a blue LED chip and a mixture of CCM:0.5%Mn4+ and commercial YAG:Ce3+ phosphors. Our results demonstrate great potential for using CCM:Mn4+ phosphors for plant growth LEDs and white light-emitting diode (WLED) applications.

On November 27, 2022, Khuat Thi Thu, a female student from the Advanced Materials and Nanotechnology program (K12) at the Faculty of Materials Science and Engineering, was honored to be among the Top 20 Outstanding Female Students and received the Vietnam Female Student in Science and Technology Award for 2022.

This prestigious annual award, organized by the Ministry of Science and Technology in collaboration with other relevant ministries and sectors since 1999, recognizes and rewards female students with outstanding academic and scientific research achievements in various cutting-edge fields of science and technology. The award aims to nurture and develop high-quality female talent, contributing to the nation's development.

Khuat Thi Thu, a young researcher from OPLAB (Optoelectronics and Photonics Research Group), achieved an impressive GPA of 3.83/4.00. She is the primary author of one paper and co-author of another presented at a national specialized conference. Thu has also participated in highly practical scientific research projects at both the university and ministry levels and has achieved numerous academic and research accolades. Additionally, she is an active participant in community volunteer activities and has received multiple certificates of merit.

This year, the award has been expanded and elevated in quality to prepare for the Fourth Industrial Revolution and the national digital transformation. It recognizes achievements in 15 fields, including Biotechnology, Computer Science, Data Communication, Software Engineering, Information Systems, Electrical and Electronic Engineering, Materials Technology, and Environmental Engineering.

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 thermal evaporation of ZnS powder. It is found that the pyramids with a based size of few micrometers are grown along different crystallographic directions and neighbored by ZnS microrods. XRD and XPS spectra showed that ZnS, ZnO, and ZnSO wurtzite phases coexist in the as-received samples. FESEM images, in situ point, and EDS elemental mapping spectra reveal that the micropyramids are composed of Zn, S, O, but each element's ratio changes with substrate temperature and is different at different faces of a single micropyramid. Using a high-spatial CL-FESEM, the profile of CL spectra along the substrate and at different faces in a single micropyramid were in-situ measured and disclosed red-shifted of ZnS band-edge emission with increasing substrate temperature, and the formation of new emission bands in the range from ∼345 to 352 nm. This new emission band is attributed to the formation of the ZnSO alloy phase. Our results demonstrated that the optical properties of the obtained ZnS/ZnO heterostructure-alloy hexagonal micropyramids could be tunned by controlling the substrate temperature and indicates potential applications of the ZnS/ZnO heterostructure alloy in optoelectronic and photonic applications.

ZnS has great potential as a valuable material for nanoscale devices because of its rich morphologies and unique structure. Although much effort has been made, the growth of high-quality ZnS crystal is still a challenge. In this paper, high-quality optically defect-free 1D ZnS nanostructures, including nanorods, nanowires, and nanobelts, were successfully synthesized on a large scale by a modified thermal evaporation method. XRD patterns and HRTEM images indicated that the ZnS nanostructures are single phases with hexagonal structures. Under optical excitation, all the ZnS nanostructures show intense UV emissions and almost no defect emissions at room temperature. Sharp UV lasing-like peaks with the FWHM as narrow as 2–3 nm are achieved for the ZnS nanobelts and nanowires. The optical transition from free exciton A, free exciton B, and their associated LO phonon replicas were determined from the evolution of the NBE emissions. These high-quality nanostructures are envisaged to be highly promising for high-efficiency light-emitting devices and lasers in the UV region.

The development of emission-tunable structures opens an optimistic future for white light-emitting diodes (WLED) utilizing a UV pump. Herein, we report emission-tunable Mn-doped ZnS/ZnO heterostructure nanobelts synthesized by the thermal evaporation method, following by an appropriate oxidation process. Under the UV excitation of 330 nm, the as-received nanobelts show an orange-yellow light with CCT of 3056 K, the 500 and 700 °C-oxidized samples strongly exhibit a warm white light emission with CCT of 3393 K and 3551 K, respectively. Surprisingly, the Mn-doped ZnS/ZnO heterostructures oxidized at 600 °C show a white light emission with CIE chromaticity coordinate of (0.31, 0.39) and CCT value of 6290 K, which are nearly very close to that of the commercial YAG:Ce3+ phosphor. A prototype WLED with the color coordinates of (0.33, 0.45), the CCT of 5491 K, and the QE ∼ 61% was successfully fabricated using Mn-doped ZnS/ZnO heterostructure nanobelts coated on the surface of UV (370 nm) chip. The obtained Mn-doped ZnS/ZnO heterostructures are promising to be applied in UV-pumped WLED fabrication.  

Hf-free n-type half-Heusler with a nominal composition of Ti0.5Zr0.5NiSn0.98Sb0.02 has been reported to have a high ZT value of almost 1.2. However, the synthesis process requires a long annealing time to achieve single-phase structure, which contributes to high product costs due to energy and time consumption. Here we introduce a new route to prepare (Ti0.5Zr0.5)1−xNbxNiSn (x = 0, 0.0050, 0.0075, 0.0100, 0.0125, 0.0150, 0.0175 and 0.0200) compounds for high thermoelectric (TE) performance along with shortening time for sample preparation. The samples were prepared by a combination of arc-melting (AM) and melt-spinning (MS) followed by spark plasma sintering process (SPS). The combination of these synthetic methods produced (Ti0.5Zr0.5)1−xNbxNiSn samples with high chemical homogeneity, single-phase structure, and fine grain about 300 nm in size, which are preferred for both charge and phonon transport properties. As a result, a maximum power factor of 44.5 µW cm−1 K−2 at 817 K and a maximum ZT of 1.19 at 874 K were achieved for the sample with x = 0.015, which are comparable to the highest ZT value reported so far for the Hf-free n-type MNiSn (M = Ti, Zr) compounds. The calculated output power density Pd and efficiency η based on a single-leg device showed an excellent performance, which yields the maximum Pd of 16.2 W cm−2 and η of 12.08% at the cold side temperature TC ≈ 305 K and the hot side temperature TH ≈ 875 K for the optimized composition with x = 0.0125. Furthermore, it is noted that the synthetic process here does not require a long-annealing time and it can be easily applied to mass production.  

Although it has been extensively studied for decades, the α-Al2O3:Cr3+ phosphor has rarely been investigated for horticultural lighting. In this work, for the first time, a prototype of a plant growth light-emitting diode (LED) has been fabricated by coating a deep-red-emitting α-Al2O3:Cr3+ phosphor onto a near-ultraviolet (NUV) chip. The α-Al2O3:Cr3+ phosphor, synthesized by a co-precipitation method and annealed at 1500 °C for 2 h, emits an outstanding narrow peak at 695 nm. The α-Al2O3:0.6%Cr3+ phosphor shows a high activation energy of 0.29 eV, a long lifetime of 3.4 ms, and a superior color purity of 100%. The chromatic coordinates and the QE value of the red LED obtained by coating an α-Al2O3:0.6%Cr3+ phosphor on a NUV chip are (x = 0.5650, y = 0.2429) and 87.1%, respectively. 

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 intensity is achieved for the ZnAl2O4:0.8%Cr3+ phosphor annealed at 1400 °C. The lifetime and activation energy of the optimal ZnAl2O4:0.8%Cr3+ phosphor annealed at 1400 °C are 25.3 ms and 0.302 eV, respectively. Three types of far-red-emitting LEDs have been successfully fabricated by coating the optimal ZnAl2O4:0.8%Cr3+ phosphor on the surface of NUV (395 nm), violet (410 nm), and green (510 nm) chips. The chromatic coordinates of the corresponding LEDs are (0.2990; 0.2199), (0.2725; 0.1594), (0.2703; 0.5743), respectively. The quantum efficiency of the ZnAl2O4:Cr3+ phosphor excited by different LEDs is calculated and reported for the first time. The obtained results indicate that the ZnAl2O4:Cr3+ phosphor has a high potential for pc-converted plant growth LED application . 

The development of full-visible-spectrum phosphors is essential for next-generation light-emitting devices with better light quality. Herein, we report on a novel broad-band-emitting phosphor based on single-composition Al-doped ZnO phosphors. Under the UV excitation of 325 nm, the ZnO : Al phosphor exhibits a full spectrum emission in the visible wavelength range from 400 to 800 nm with a CIE chromaticity coordinate of (0.42, 0.48), a quantum efficiency of 43%, a color rendering index (CRI) of 74, a correlated color temperature (CCT) value of 3873 K and an activation energy of 0.22 eV. A prototype of a UV-pumped warm WLED with a high CRI of 87 and a CCT of 4067 K has been achieved by using only this broad-band-emitting Al3+-doped ZnO phosphor. The obtained results indicate that the single-composition Al3+-singly doped warm white emitting phosphor is a promising candidate for UV-pump warm white light-emitting diodes. 

Narrow-band red-emitting phosphor Cr3+-doped BaMgAl10O17 (BAM) was successfully synthesized via a sol – gel method. The obtained Cr3+-doped BaMgAl10O17 phosphor with average particle size of about 1 μm emits an intense red light at around 695 nm with two broad excitation bands at 405 and 560 nm. The highest PL intensity is achieved at the Cr3+ doping concentration of 1 mol% and the annealing temperature of 1400 °C. The Tanabe-Sugano diagram reveals that Cr3+ ions are affected by the strong crystal field with the Dq/B ratio value of ~2.7, and the peak at 695 nm is attributed to the 2E→4A2 transitions of Cr3+ ions. A purple LED with colour coordinates of (0.263, 0.148) has been fabricated by coating the Cr3+-doped BaMgAl10O17 phosphor on a violet LED (410 nm) chip. The results indicate that BaMgAl10O17:Cr3+ phosphor could be promising red phosphor for plant growth LEDs. 

As hydrogen gas increasingly becomes critical as a carbon-free energy carrier, the demand for robust hydrogen sensors for leak detection and concentration monitor will continue to rise. However, to date, there are no lightweight sensors capable of meeting the required performance metrics for the safe handling of hydrogen. Here, we report an electrical hydrogen gas sensor platform based on a resistance nanonetwork derived from Pd-Co composite hole arrays (CHAs) on a glass substrate, which meets or exceeds these metrics. In optimal nanofabrication conditions, a single poly(methyl methacrylate)(PMMA)-coated CHA nanosensor exhibits a response time (t80) of 1.0 s at the lower flammability limit of H2 (40 mbar), incredible sensor accuracy (<1% across 5 decades of H2 pressure), and an extremely low limit of detection (LOD) of <10 ppb at room temperature. Remarkably, these nanosensors are extremely inert against CO and O2 gas interference and display robust long-term stability in air, suffering no loss of performance over 2 months. Additionally, we demonstrate that the unique nanomorphology renders the sensors insensitive to operation voltage/current with diminutive power requirement (∼2 nW) and applied magnetic field (up to 3 kOe), a crucial metric for leak detection and concentration control. 

Non-rare-earth dual green and red-emitting Mn-doped ZnAl2O4 phosphors were successfully synthesized by a co-precipitation method. XRD and XPS spectra reveal that Mn ions in two valence states Mn2+ and Mn4+ are co-existed in the ZnAl2O4 host lattice. The ZnAl2O4:(Mn2+, Mn4+) phosphors exhibit two intense emission bands in the green and red spectral regions, peaking at 510 and 679 nm. It is demonstrated that the PL intensity ratio of green emission and red emission (IGreen/Ired) can simply be controlled by adjusting the annealing temperature and found to vary from 2.78 to 0.48 when increasing the temperature from 1200 to 1400 °C. A prototype red-emitting LED was fabricated using a 310-nm UV LED combined with the ZnAl2O4:0.5% (Mn2+, Mn4+) phosphor. The CIE color coordinates are x = 0.5643 and y = 0.2798, while the red-emitting LED is driven by 60 mA current. The quantum efficiency (QE) of the ZnAl2O4:0.5%Mn phosphor is estimated to be about 27.3%. To the best of our knowledge, this is the first time that the QE of Mn-doped ZnAl2O4 phosphor is reported. 

Orange-red-emitting AlPO4:Eu3+ phosphors have been systematically synthesized by a co-precipitation method. Under the excitation at 394 nm these phosphor shows strong orange-red emissions with the strongest peaks at 588, 594, 685 and 700 nm. The highest PL intensity is achieved at the dopant concentration of 3 mol% and the annealing temperature of 1000 °C. Additionally, 84% of the room-temperature emission intensity is still maintained at 160 °C, indicating a good thermal stability and practicality. By a Judd-Ofelt (JO) analysis, it is demonstrated that the symmetry sites surrounding Eu3+ ions are influenced by the dopant level. The lowest value of Ω2/Ω4 ratio of 0.27 reveals the highest symmetry site at the Eu3+ concentration of 3 mol%. The CIE 1931 color chromaticity coordinates (x, y) and the activation energy of the AlPO4:3%Eu3+ phosphor are (0.5602; 0.3862) and 0.28 eV, respectively. The color coordinates of the phosphor coated on NUV LED chip and its quantum efficiency (QE) are (0.5573, 0.3253) and 38.7%, respectively. To the best of our knowledge, this is the first time that a calculated QE of AlPO4:Eu3+-based orange-red-emitting LED is reported. The obtained results show a great potential of using orange-red-emitting AlPO4:Eu3+ phosphor for WLED application.  

Metal chalcogenides have attracted attention as potential thermoelectric materials due to their intrinsically low thermal conductivity arising from their layered structure with weak van der Waals atomic bonding. InSe, one of the post transition metal chalcogenides, also has low thermal conductivity and doping of InSe with elements such as Sn, Si, and As is known to improve the electronic transport properties. Herein, we investigated Te doping in Si-doped InSe (In0.9Si0.1Se) and report enhanced thermoelectric properties, mainly the increased Seebeck coefficient due to the increase in effective mass. Due to the increase in effective mass, the magnitude of the Seebeck coefficient systematically increased with Te doping from 234 µV/K to 405 µV/K. Eventually, the zT at 700 K was enhanced from 0.040 for the pristine sample to 0.069–0.096 for the Te-doped samples 

Khuat Thi Thu is a second-year student at the Faculty of Materials Science and Engineering. She joined our group when she was a freshman. She won the top prize in Phenikaa's Scientific Research Contest 2020 for Students and was selected as one of the best students among the university to participate in Vietnam's National Scientific Research Contest 2020. This research project entitled: "Synthesis and Investigation on Optical Properties of one-dimensional ZnS/MoS2 materials" was supervised by Prof. Dr. Pham Thanh Huy. 

The awards ceremony for the contest took place in Ho Chi Minh on 27 November. The annual event is co-organised by the Ministry of Education and Training, the Central Committee of the Ho Chi Minh Communist Youth Union, the Ministry of Science and Technology, and the Viet Nam Union of Science and Technology Associations. The competition is to help Vietnamese students satisfy their passion for scientific research, and turn the theory they learn in their schools into prototypes for technological solutions to real-world problems.

Quantum Resistive pressure Sensors (pQRS) can be integrated into flexible electronics, smart textiles, robotics etc. Our last research on hybrid nanocomposites by 3D spraying, highlights the positive input of graphene combined with carbon nanotubes to build a robust hierarchical conducting architecture. Our best formulation of pQRS transducers, thermoplastic polyurethane (TPU) functionalized pG2%/CNT4% hybrid, exhibited a linear response from 0 to 4 MPa, the highest range ever obtained with a sensitivity as high as 11.29 × 10−5 kPa−1. Graphene allowed to multiply by three the piezo-resistive response to compression (Ar) of TPU-CNT up to 60% and improved significantly sensors’ stability. More strikingly, hybrid pQRS can convert the classical double peak of the signal resulting from the poisson’s effect at high compression, into a single peak. This performance is an exciting result ascribed to the hybridization of carbon nanotubes (CNT) with pristine graphene (pG) into an architecture keeping contact whatever the direction of solicitation. Hybrid pQRS had also a more stable piezo-resistive behavior whatever the speed of compression, and the mechanical history. Finally, the proof of concept of pressure monitoring and mapping, with a flexible and integrable array of four hybrid pQRS has demonstrated a promising potential for real time sensing. 

We studied spin dynamics of charge carriers in the superlattice-like Ruddlesden-Popper hybrid lead iodide perovskite semiconductors, 2D (BA)2(MA)Pb2I7 (with MA = CH3NH3, and BA = CH3(CH2)3NH3), and 3D MAPbI3 using the magnetic field effect (MFE) on conductivity and electroluminescence in their light emitting diodes (LEDs) at cryogenic temperatures. The semiconductors with distinct structural/bulk inversion symmetry breaking, when combined with colossal intrinsic spin–orbit coupling (SOC), theoretically give rise to giant Rashba-type SOC. We found that the magneto-conductance (MC) magnitude increases monotonically with the emission intensity and saturates at ≈0.05% and 0.11% for the MAPbI3 and (BA)2(MA)Pb2I7, respectively. The magneto-electroluminescence (MEL) response with similar line shapes as the MC response has a significantly larger magnitude, and essentially stays constant at ≈0.22% and ≈0.20% for MAPbI3 and (BA)2(MA)Pb2I7, respectively. The sign and magnitude of the MC and MEL responses can be quantitatively explained in the framework of the Δg-based excitonic model using rate equations. Remarkably, the width of the MEL response in those materials linearly increases with increasing the applied electric field, where the Rashba coefficient in (BA)2(MA)Pb2I7 is estimated to be about 7 times larger than that in MAPbI3. Our studies might have significant impact on future development of electrically-controlled spin logic devices via Rashba-like effects. 

In this work, far-red-emitting Zn2SnO4 phosphor has been successfully synthesized by a facile modified solid-state reaction method from ZnO and SnO2 powders. FESEM images reveal that as-milled particles are nearly spherical, with size in the range of 10–30 nm. The particle size increases with increasing annealing temperature and it reaches the value of about 4 μm at 1200 °C. XRD patterns indicate that Zn2SnO4 phase starts occurring at ~700 °C with its single phase at 900 °C and the best crystalline quality of Zn2SnO4 phase is obtained at 1000 °C. UV–Vis spectra analysis reveals that ZnO phase reappears at high annealing temperature (≥1100 °C), reflecting the deterioration of the single phase of Zn2SnO4. A broad visible band centered at 684 nm, which has never been explicitly reported, is clearly observed in the PL spectrum of the single Zn2SnO4 crystals. The intensity of this new band is influenced by annealing temperatures. It reaches the maximum value at 1000 °C, corresponding to the highest quality of the Zn2SnO4 phase. By using data fitting, the PL spectrum is deconvoluted into four Gaussian peaks at ~2.20 eV (563.5 nm), ~1.98 eV (626.1 nm), ~1.80 eV (688.8 nm), and ~1.68 eV (738.0 nm). The peak at ~2.20 eV (563.5 nm) is ascribed to oxygen vacancy (Vo) while the other emission peaks are possibly associated with a significant number of trapped states due to the high concentration of deficiencies such as oxygen vacant defects, zinc interstitials, zinc/tin vacancies (VZn/VSn), Zn/Sn stoichiometry or point defects.  

We develop a novel approach to create oxygen vacancies on the surface of ZnO particles and investigate their role in the photoluminescence of the ZnO. In this approach, the commercial ZnO powder is coated with a thin carbon layer using ball-milling technique, forming ZnO@C core@shell particles. By annealing the as-milled ZnO@C at a relatively low temperature (i.e., up to 600 °C) in oxygen, the surface oxygen vacancies are formed, which is confirmed by X-ray photoelectron spectroscopy analyses. The annealed powders show red photoluminescence, which largely covers the far-red region, and by varying the annealing temperature, the emission range of the ZnO can be tailored. We found that the far-red emission is associated with the surface oxygen vacancies of ZnO 

In frame of this talk, Prof. HUY also explained the idea and the important role of the Preparation, Goal and Self-studying in the students' life. 

See at link: https://www.youtube.com/watch?v=AfB7OVCHBFc&t=4s&fbclid=IwAR2yobOyg1gK4mHW3lU6Q84Fg1QZkHumyplxkvBocdNGzen4cC1OpaW4Bq4