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White lighting sources based on laser diodes (LDs) are strongly regarded as the next generation of high luminance lighting sources because the luminous efficiency of LDs increases linearly with operating current, which can resolve the “efficiency droop” of LEDs. To facilitate the advent of high brightness solid state lighting, searching for a light convertor with high thermal stability, high conversion efficiency, and irradiation stability is essential. Herein, we developed a robust light convertor, YAG:Ce3+ based on phosphor-in-glass (denoted as YAG-PiG), exhibiting a quantum efficiency of 70.1% and a high thermal conductivity of 0.89 W m−1 K−1. The microstructure and luminescent properties of YAG-PiG were also investigated in detail. Compared to YAG-PiS (phosphor-in-silicone), this YAG-PiG shows an overall increase in irradiation and thermal stability performances. A high power white LDs was constructed by coupling the YAG-PiG with a 445 nm blue laser and a sapphire plate modified by an antireflection layer and a blue-pass filter serving as the heat sink. The constructed PiG converted LDs@sapphire exhibits a luminous efficacy of 217 lm W−1 and a CRI (color rendering index) of 57 at 3646 K under a driven power of 3 W. Compared to the conventional white LDs, the luminous efficacy and the resistance to laser irradiation of the white LDs@sapphire are obviously enhanced. Therefore, we predict that this white emitting PiG converted LDs@sapphire will become a promising candidate for future lighting sources and promote the use of sapphire plate as the heat sink.

A study of the uniform deposition of nanoparticles across a 300-mm wafer was conducted to assess the uniformity of the wafer center-to-edge cleaning technique. A new method of particle deposition was devised different from the conventional method using electrostatic force. The strategy implements wafer rotation and deposition through principles of convection and diffusion. In this study, we focused on the effect of wafer rotation speed on particle deposition. After determining optimum conditions, fine results were obtained with a well-deposited shape and an excellent particle size uniformity of above 70% over the entire area of the wafer except in unusual cases. Deposition results were confirmed with KLA-Tencor Surfscan SP5 commonly used by foundries, and logic and memory manufacturers around the world to increase node development and production. The inherent index of the refraction value by Surfscan SP5 caused a particle size shift in measurement results. However, scanning electron microscopy and scanning mobility particle sizer analysis results revealed that 80-, 60-, 40-, 30-, and 20-nm-sized silica nanoparticles were well deposited on the wafer. Through this research, we believe that standard wafers processed with this particle deposition method will be useful for performance evaluation of wafer cleaning technology and calibration of wafer inspection technology during development.

High-power and high-brightness solid state laser lighting sources, fabricated with high-power blue laser diodes (LDs) and yellow-emitting phosphor converters, constitute a pioneering lighting technology for specialized lighting. Because of the high radiation flux and thermal stress produced by high-power blue LDs, there is an urgent need for a light converter with excellent heat-resistance and thermal stability. In this work, YAG:Ce phosphor-in-glass (PiG), prepared by embedding YAG:Ce phosphor in glass matrix, was developed. Because of the good chemical stability between the glass matrix and the phosphor as well as high refractive index of 1.84 of the glass matrix, the internal quantum efficiency of YAG:Ce-PiG material can reach up to 78.9% under 445 nm blue laser excitation. In comparison with reported papers, the content of the YAG phosphor in this PiG can reach up to 29 wt%, thus it can get more brightness when excited by higher LD power. Besides, systematic research on the thermal effect to the material and its luminescent properties when excited by a high-power blue LD is done in detail. Compared with traditional commercial phosphor-in-silicone (PiS) light converters, PiG can withstand higher blue LD power and maintain a higher luminescent intensity. By virtue of its better heat-resistance performance under exposure to high-power blue LD, the developed PiG light converter material is an ideal choice to replace traditional commercial PiS in high brightness lighting sources.

β-Sialon:Eu2+ has been reported to be the most promising narrow-band green phosphor for wide color gamut LCD backlights, but the coexistence of the Eu3+ luminescence killer with the Eu2+ luminescence center limits its luminescence performance to a great extent. In this study, we propose a direct reduction strategy to successfully realize the reduction of Eu3+ to Eu2+ and, finally, increase the effective concentration of Eu2+ in the crystal lattice and greatly minimize the amount of Eu3+ on the particle surface. As a result, the luminescence of treated β-sialon:Eu2+ is enhanced by 2.3 times, and the internal quantum efficiency significantly increases from 52.2 to 96.5%. The mechanisms for such large enhancements in luminescence are clarified by investigating the microstructure, luminescence spectra, valence state, concentration, and distribution of Eu using a variety of chemical analyses. We find that the low efficiency is ascribed to the coexistence of the Eu3+ luminescence killer with the Eu2+ luminescen...

The (Y,Ce) 2 BaAl 4 SiO 12 phosphor, a garnet-structured blue-to-yellow color convertor for WLED, exhibits an interesting “microcrystal-glass powder” feature, which can be regarded as the 4th form for phosphor, in addition to the “ceramic powder phosphor”, the “single crystal phosphor” and the “glass-ceramic phosphor”. The structure exhibits luminescent microcrystals embedding in non-luminescent glass matrix: the spherical crystals are mainly arranged around the glass phase forming a “necklace” pattern, while the individual crystals show a “core-shell” architecture regarding the luminescence intensity variation. Further combining the phase evolution evidence evaluated by Rietveld refinement, we propose the formation mechanism for such unique morphology/structure as a two-stage process, including an initial nucleation by solid state reaction and following liquid-assisted crystal growth, instead of a precipitation-crystallization process.

Superhigh brightness, reliability, and modularization are three key features of state-of-the-art high-brightness solid state lighting, such as high-power white light-emitting diodes (white LEDs) and white laser diodes (white LDs). However, these features are inevitably limited by the organic resin packing material, as a crucial component of the white lighting device, because of its unstable property at high temperature and low thermal conductivity. Here, we report a robust light convertor that can simultaneously play key roles as a phosphor and an alternative encapsulating material via phosphor-in-glass (PiG) engineering. We employed a combination of powder X-ray diffraction, scanning electron microscope, energy dispersive spectrometer (EDS), EDS mapping, confocal laser scanning microscope, cathodoluminescence mapping, in conjunction with micro-PL system with a point-by-point scanning mode to study the detailed structure of PiG samples. This Y3Al5O12:Ce3+-based PiG exhibits a high external quantum efficie...

A low band-gap polymer, PTB7-Th, is one of the typical p-type semiconductors among the next-generation solar-cell materials that have achieved power conversion efficiencies of over 10%. However, the internal deterioration mechanism of high-efficiency polymer solar cells such as PTB7-Th-based cells is still an open issue and has been extensively studied. Here, we report a study with operando electron spin resonance (ESR) spectroscopy for PTB7-Th polymer solar cells with an n-type semiconductor PC

To clarify the bright contrast of insulating ceramics in secondary electron (SE) image taken using scanning electron microscopy (SEM), the low-pass secondary electron signals and images of conductive AlN and insulating β-SiAlON powders taken by fountain detector (FD) were inspected. It was found that the background component of β-SiAlON is originally strong. This component may come from the SE acceleration according to the charging. The low energy SEs of 5–20 eV were strong in AlN particles. According to the wide acceptance angle of FSED, we could not detect clear energy shift in SE spectra. These observations suggest that the bright contrast of insulating materials is not an intrinsic character of insulators but the SE3 contribution.

As an excellent red phosphor, CaAlSiN3:Eu2+ plays a major role in high color rendition or wide color gamut white light-emitting diodes, but it can hardly be used in high-power laser displays and lighting due to the intrinsic low thermal performance of the phosphor/silicone resin mixture. To apply CaAlSiN3:Eu2+ in laser lighting devices, a bulk ceramic form is thus required to survive thermal attack and high flux density irradiation. However, it remains an unsolved great challenge to fabricate fully densified CaAlSiN3:Eu2+ ceramics. Here, for the first time, translucent CaAlSiN3:Eu2+ ceramics with an interesting composite microstructure, where red-emitting phosphor particles with a core–shell structure are uniformly embedded in a non-luminescent α-Sialon matrix, are successfully synthesized using Si3N4 and SiO2 as sintering additives. The luminescence ceramic is superior to the corresponding powder phosphor in terms of its enhanced thermal stability (15% increase) and thermal conductivity (4 W m−1 K−1). It has a high external quantum efficiency of 60% (87% that of the powder) upon 450 nm excitation, and a luminous efficacy of 10.6 lm W−1 when irradiated under a blue laser flux density of 0.75 W mm−2. The translucent CaAlSiN3:Eu2+ ceramic is thus supposed to be a potential color converter used in emerging laser lighting and display technologies.

We present a general phenomenological model for surface second-harmonic generation (SSHG) induced by strain fields with up to three spatial coordinates. As an example, we apply it to thermal-mismatch strain fields around cylindrical metallic through-silicon-vias (TSVs) embedded in an Si(001) surface, which are widely used as interconnects between vertically stacked silicon layers to achieve 3D integration. We find that analysis of the four different combinations of s or p incoming and outgoing polarizations enables reconstruction of the strain field. In particular, the sS combination yields tensorial components of the strain field that are different from zero; from this information, the pP, sP, and pS combinations complete the analysis of the strain field.

Piezoelectric and ferroelectric properties in the two dimensional (2D) limit are highly desired for nanoelectronic, electromechanical, and optoelectronic applications. Here we report the first experimental evidence of out-of-plane piezoelectricity and ferroelectricity in van der Waals layered ${\alpha}$-In2Se3 nano-flakes. The non-centrosymmetric R3m symmetry of the ${\alpha}$-In2Se3 samples is confirmed by scanning transmission electron microscopy, second-harmonic generation, and Raman spectroscopy measurements. Domains with opposite polarizations are visualized by piezo-response force microscopy. Single-point poling experiments suggest that the polarization is potentially switchable for ${\alpha}$-In2Se3 nano-flakes with thicknesses down to ~ 10 nm. The piezotronic effect is demonstrated in two-terminal devices, where the Schottky barrier can be modulated by the strain-induced piezopotential. Our work on polar ${\alpha}$-In2Se3, one of the model 2D piezoelectrics and ferroelectrics with simple crystal structures, shows its great potential in electronic and photonic applications., Comment: 17 pages, 5 figures, just accepted by Nano Letters

The strong advantage of two-dimensional (2D) materials is that they exhibit interesting physical properties down to the single unit layer (typically less than 1 nm). Such emergent properties are highly dependent on thickness and can be tunable via external parameters such as electric field, pressure, and/or chemical treatment. In addition, most 2D materials have hexagonal crystal structures; thus, it is possible to stack with other 2D materials to enrich the properties. This tunability and compatibility makes 2D materials and their heterostructures promising candidates for optoelectronic devices.

Major challenge in nanotechnology is to improve the solar cells efficiency. This can be achieved by controlling the silicon solar cell wafer surface structure. Herein, we report a KOH wet etching process along with an ultrasonic cleaning process to improve the surface texture of silicon solar cell wafers. We evaluated the KOH temperature, concentration, and ultra-sonication time. It was observed that the surface texture of the silicon solar wafer changed from a pyramid shape to a rectangular shape under edge cutting as the concentration of the KOH solution was increased. We controlled the etching time to avoid pattern damage and any further increase of the reflectance. The present study will be helpful for the mass processing of silicon solar cell wafers with improved reflectance.

Although different gender associations between self-rated health (SRH) and mortality have been reported, the results of the respective studies have been inconsistent and little is known about the cause-specific relation of mortality with SRH by gender. Therefore, to evaluate the gender differences in all-cause or specific causes of mortality by SRH, this retrospective cohort study was conducted using the data of 19,770 Korean adults aged 50 years and over who underwent health screening at Seoul National University Hospital between March 1995 and December 2008. SRH was surveyed using a simple questionnaire, and the all-cause mortality and cause-specific mortality were followed up from baseline screening until December 31, 2016. Results showed that the relationship between SRH and all-cause mortality differed by gender, and the differences also varied depending on the cause of death. In men, the adjusted hazard ratio (aHR) of all-cause mortality was higher in the poor SRH group than the very good SRH groups even after adjustment for socio-demographic, clinical, and behavioral risk factors (aHR:1.97, 95% CI 1.51-2.56), and these results were similar to those for cancer, cardiovascular, and respiratory disease mortalities (aHR:1.52, 95% CI 0.93-2.50; aHR: 2.11, 95% CI 1.19-3.74; aHR:10.30, 95% CI 2.39-44.44, respectively). However, in women, the association between SRH and all-cause mortality was insignificant, and inverse relationships were found for cardiovascular and respiratory disease mortalities in the poor and very good SRH groups. Cancer mortality had a positive relation with SRH (aHR: 1.14, 95% CI 0.75-1.72; aHR: 2.58, 95% CI 1.03-6.48; aHR: 0.49, 95% CI 0.24-0.98; aHR: 0.15, 95% CI 0.04-0.57: all-cause, cancer, cardiovascular, and respiratory disease mortalities, respectively). Clinicians need to take these gender differences by SRH into account when evaluating the health status of over-middle aged adults.

Aluminum oxynitride (AlON), which is conventionally used as one of the ceramics with good thermal and chemical stability, has an attractive candidate for a tunable extreme UV luminous material due to its unique combination of properties and UV luminescence. In this paper, we have synthesized the novel AlON UV emitting materials, which have a wavelength from 4.29 to 4.54 eV, and discovered the core (AlON)-shell (Al2O3) like structures in a transmission electron microscopy. Furthermore, their potential application in a UV light emitter has been demonstrated by applying the combination with a CNT field emission cold cathode, which has been made by a simple printing method. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Graphene and related two-dimensional materials are promising candidates for atomically thin, flexible, and transparent optoelectronics. In particular, the strong light-matter interaction in graphene has allowed for the development of state-of-the-art photodetectors, optical modulators, and plasmonic devices. In addition, electrically biased graphene on SiO2 substrates can be used as a low-efficiency emitter in the mid-infrared range. However, emission in the visible range has remained elusive. Here we report the observation of bright visible-light emission from electrically biased suspended graphenes. In these devices, heat transport is greatly minimised; thus hot electrons (~ 2800 K) become spatially localised at the centre of graphene layer, resulting in a 1000-fold enhancement in the thermal radiation efficiency. Moreover, strong optical interference between the suspended graphene and substrate can be utilized to tune the emission spectrum. We also demonstrate the scalability of this technique by realizing arrays of chemical-vapour-deposited graphene bright visible-light emitters. These results pave the way towards the realisation of commercially viable large-scale, atomically-thin, flexible and transparent light emitters and displays with low-operation voltage, and graphene-based, on-chip ultrafast optical communications., Comment: 63 page

Nitride and oxynitride (Sialon) phosphors are good candidates for the ultraviolet and visible emission applications. High performance, good stability and flexibility of their emission properties can be achieved by controlling their composition and dopants. However, a lot of work is still required to improve their properties and to reduce the production cost. A possible approach is to correlate the luminescence properties of the Sialon particles with their local structural and chemical environment in order to optimize their growth parameters and find novel phosphors. For such a purpose, the low-voltage cathodoluminescence (CL) microscopy is a powerful technique. The use of electron as an excitation source allows detecting most of the luminescence centers, revealing their luminescence distribution spatially and in depth, directly comparing CL results with the other electron-based techniques, and investigating the stability of their luminescence properties under stress. Such advantages for phosphors characterization will be highlighted through examples of investigation on several Sialon phosphors by low-energy CL.

Silicon dioxide (SiO2) is one of the key materials in many modern technological applications such as in metal oxide semiconductor transistors, photovoltaic solar cells, pollution removal, and biomedicine. We report the accidental discovery of free-standing grassy silica nanoribbons directly grown on SiO2/Si platform which is commonly used for field-effect transistors fabrication without other precursor. We investigate the formation mechanism of this novel silica nanostructure that has not been previously documented. The silica nanoribbons are flexible and can be manipulated by electron-beam. The silica nanoribbons exhibit strong blue emission at about 467 nm, together with UV and red emissions as investigated by cathodoluminescence technique. The origins of the luminescence are attributed to various defects in the silica nanoribbons; and the intensity change of the blue emission and green emission at about 550 nm is discussed in the frame of the defect density. Our study may lead to rational design of the new silica-based materials for a wide range of applications.

We study the nonlinear optical response in a strained thin film ferroelectric oxide BaTiO3 using piezoelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 (001) as a variable strain substrate and La-doped SrTiO3 as a conductive buffer layer. The rotation-anisotropic second harmonic intensity profile shows hysteretic modulation corresponding to the strain variation from the inverse piezoelectric response of the substrate. An enhancement of 15% is observed at 1.2 kV/cm, while a control sample shows negligible change as a function of piezovoltage. Reflection high-energy electron diffraction, x-ray photoelectron spectroscopy, and high-resolution scanning transmission electron microscopy reveal the epitaxial interface. X-ray diffraction and piezoresponse force microscopy confirm tetragonal distortion and ferroelectricity of the BaTiO3 overlayer. Our results suggest a promising route to enhance the performance of nonlinear optical oxides for the development of future nano-opto-mechanical devices.

We investigate polarization retention in 10 to 19 nm thick ferroelectric BaTiO3 (BTO) grown on Ge(001) by molecular beam epitaxy. The out-of-plane direction and reversibility of electric polarization were confirmed using piezoresponse force microscopy. After reverse-poling selected regions of the BTO films to a value P with a biased atomic-force microscope tip, we monitored relaxation of their net polarization for as long as several weeks using optical second-harmonic generation microscopy. All films retained reversed polarization throughout the observation period. 10 nm-thick BTO films relaxed monotonically to a saturation value of 0.9 P after 27 days and 19 nm films to 0.75 P after 24 h. Polarization dynamics are discussed in the context of a 1D polarization relaxation/kinetics model.

Microscopic characterization of radical states in organic light‐emitting diodes (OLEDs) during device operation is useful for elucidating the degradation mechanism because the radical formation has been considered as non‐radiative recombination centers. Electron spin resonance (ESR) spectroscopy is suitable for such characterization because it can directly observe radicals in OLEDs. In this work, the detailed ESR investigation into the radical states in OLEDs during device operation is firstly reported using a typical light‐emitting Alq3‐based OLEDs. The simultaneous measurements of the ESR signal and the luminance of the same OLED are performed to study the direct correlation between the radical states and the performance degradation. These characteristics show that the luminance monotonically decreases and an ESR signal concomitantly increases as the duration of the device operation increases after operating the OLED. Using the analysis of density functional theory (DFT) calculation, the origin of the newly emerged ESR signal is ascribed to the cationic species due to decomposed Alq3 molecules. The elucidation of the radical species formed in OLEDs during device operation has been demonstrated at a molecular level for the first time. This ESR analysis would provide useful knowledge for understanding the degradation mechanism in the OLEDs at the molecular level.

Electrical characteristics of leakage current paths in vertical-type n-GaN Schottky barrier diodes (SBDs) on free-standing GaN substrates are investigated by using photon emission microscopy (PEM). The PEM mapping shows that the initial failure of the SBD devices at low voltages is due to the leakage current paths from polygonal pits in the GaN epilayers. It is observed that these polygonal pits originate from carbon impurity accumulation to the dislocations with a screw-type component by microstructure analysis. For the SBD without polygonal pits, no initial failure is observed and the first leakage appeals at the edge of electrodes as a result of electric field concentration. The mechanism of leakage at pits is explained in terms of trap assisted tunneling through fitting current-voltage characteristics.

Super-high brightness, reliability, and modularization are three key features of state-of-the-art high-brightness solid state lighting, such as high-power white light-emitting diodes (white LEDs) and white laser diodes (white LDs). However, these features are inevitably limited by the organic resin packing material, as a crucial component of the white lighting device, because of its unstable property at high temperature and low thermal conductivity. Here, we report a robust light convertor that can simultaneously play key roles as a phosphor and an alternative encapsulating material via phosphor-in-glass (PiG) engineering. We employed a combination of powder X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), EDS mapping, confocal laser scanning microscope (CLSM), cathodoluminescence (CL) mapping, in conjunction with micro-PL system with a point-by-point scanning mode to study the detailed structure of PiG samples. This Y3Al5O12:Ce3+-based PiG exhibits a high external quantum efficiency of ~60%, a high thermal conductivity of ~0.59 W/mK, exceptional thermal stability, and excellent moisture resistance. By combining the as-synthesized PiG with high-power blue chip-on-board (COB), a high luminous efficacy (92 lm/W) modular white LEDs with a luminous flux up to 1076 lm and a high color rendering modular warm white LEDs (Ra = 90.3 and CCT = 3585 K) are achieved. Moreover, a modular white LDs with a higher luminous efficacy (110 lm/W) is also achieved through blue LDs pumping. The results demonstrate that this easy-fabrication, low-cost, and long-term reliable high-brightness modular white LEDs or white LDs is expected to be a promising candidate for next-generation illumination.

Precise doping control is of critical importance in power device fabrication using widegap materials. In this study, we characterize pn-junctions in GaN and SiC by cathodoluminescence. To improve spatial resolution, the specimens were polished using cross-sectional polisher. GaN specimens were successfully characterized with line profile of CL spectra across the cross-section. On the other hand, CL data could not be used straightforwardly for characterization of pn-junctions in the case of SiC.