All‐inorganic CsPbX3 (X=I, Br, Cl) perovskite quantum dots (PQDs) have been investigated because of their optical properties, such as tunable wavelength, narrow band, and high quantum efficiency. ...These features have been used in light emitting diode (LED) devices. LED on‐chip fabrication uses mixed green and red quantum dots with silicone gel. However, the ion‐exchange effect widens the narrow emission spectrum. Quantum dots cannot be mixed because of anion exchange. We address this issue with a mesoporous PQD nanocomposite that can prevent ion exchange and increase stability. We mixed green quantum‐dot‐containing mesoporous silica nanocomposites with red PQDs, which can prevent the anion‐exchange effect and increase thermal and photo stability. We applied the new PQD‐based LEDs for backlight displays. We also used PQDs in an on‐chip LED device. Our white LED device for backlight display passed through a color filter with an NTSC value of 113 % and Rec. 2020 of 85 %.
Points of light: Green CsPbBr3 perovskite quantum dots (PQDs), embedded in mesoporous silica (MP), were mixed with red CsPb(Br0.4I0.6)3 quantum dots in a silicone resin and placed on an InGaN blue chip. The green and red QDs were excited by blue light with λ=450 nm. The resulting PQD white light emitting diode (LED) exhibits a wide color gamut because of its narrow emission wavelength.
Two types of infrared fluoride phosphors, Cr3+-doped K3AlF6 and K3GaF6, were developed in this research. The K3Al1–x F6:xCr3+ and K3Ga1–y F6:yCr3+ fluoride phosphors were proven to be pure phase via ...X-ray diffraction refinement, which demonstrated that the procedure can be applied to large-scale production. Electron paramagnetic resonance measurements indicated that Cr3+ ions in cubic with respect to noncubic are coupled better with K3GaF6 than with K3AlF6. The main differences between these two phosphors, the site symmetry and pressure behavior of the spectra, were obtained in temperature- and pressure-dependent spectra. According to the calculation results, Cr3+ in fluorine coordination at ambient pressure indicates an intermediate crystal field. For the phosphor-converted light-emitting diodes (LEDs) fabricated from these two phosphors, the spectral range is from 650 to 1000 nm, which resulted in a radiant flux of 7–8 mW with an input power of 1.05 W. The research reveals detailed luminous properties, which will lead to a new way of studying Cr3+-doped fluoride phosphors and their application in LEDs.
Perovskite quantum dots usually possess excellent optical properties, such as high color purity, high photoluminescence quantum yield, and tunable emission wavelength. However, their relatively low ...stability against heat, water, oxygen, and light hinders their practical applications in the field of optoelectronic devices. Herein, melt‐quenching and heat treatment crystallization methods are used to fabricate the CsPbBr3@glass. Atomic layer deposition and the sol–gel method are applied to encapsulate the CsPbBr3@glass with a dense SiO2 layer and hydrophobic SiO2 layer, respectively, to further improve the water resistance, thermal reversibility of photoluminescence, and photostability. The CsPbBr3@glass@ASG can be synthesized with the triple layer encapsulation of the glass matrix, dense SiO2 layer, and hydrophobic SiO2 layer. During the water resistance test for seven weeks, CsPbBr3@glass@ASG can preserve ≈100% of initial PL intensity. Similarly, it can preserve ≈100% of PL intensity after five continuous heating–cooling cycles between 30 and 100 °C. In addition, the internal and external quantum efficiencies of CsPbBr3@glass@ASG can still be maintained at 42.0% and 33.7%, respectively. Results indicate that CsPbBr3@glass@ASG can provide a balance between optical properties and extrinsic stability successfully, thereby becoming a potential candidate material for practical applications related to optoelectronic devices in the future.
CsPbBr3@glass@ASG composite material with triple‐layer encapsulation, including a glass matrix, dense SiO2 layer, and hydrophobic SiO2 layer, is synthesized. With the triple encapsulated protection, the water resistance and thermal reversibility of photoluminescence can be preserved at ≈100%.
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•A microfluidic synthesis process for CsPbBr3/Cs4PbBr6 NCs was optimized.•Colloidal CsPbBr3/Cs4PbBr6 NCs with the highest PLQY of 86.9% were obtained.•A luminescent ink was produced ...by the as-synthesized CsPbBr3/Cs4PbBr6 NCs.•The ink was used to print large high-resolution patterns and fabricate mini-LED.•The narrow green emission of the mini-LED well obeyed the Rec. 2020 standard.
Zero-dimensional Cs4PbX6 (X = Cl, Br, I) perovskite material is recognized as a potential luminescent material and host owing to its excellent optical properties. However, the synthesis of large-scale CsPbBr3/Cs4PbBr6 complex nanocrystals (NCs) is difficult, and their application in mini- or micro-LEDs remains limited. Herein, we applied a microfluidic system for a simple, continuous, and stable synthesis of CsPbBr3/Cs4PbBr6 NCs. The CsPbBr3/Cs4PbBr6 complex NCs were obtained after the optimization of the Cs/Pb precursor ratio and alkaline environment, and their photoluminescent quantum yield is up to 86.9%. These as-synthesized CsPbBr3/Cs4PbBr6 NCs were used to produce a luminescent ink with the optimization of different solvents. This ink was successfully used to print large and high-resolution patterns, and fabricated mini-sized color-converted LED. The narrow green emission of the LED well obeyed the requirements of the Rec. 2020 standard, demonstrating the potential of this material in the inkjet printing applications of color-converted mini- or micro-LED arrays.
High-power vertical-cavity surface-emitting laser (VCSEL) arrays, which can serve as the light source in modern lidar and three-dimensional optical sensing systems, have recently attracted a lot of ...attention. In these types of systems, the time-of-flight (ToF) technique, based on the round-trip time of short optical pulses is usually adopted. Further enhancement of the ranging distance and depth resolution in these ToF driven systems by the incorporation of a VCSEL array with a high available power, high brightness (narrow divergence angle), and fast response time is highly desirable. However, a large number of light emission apertures (several hundreds) in the VCSEL array is usually necessary to raise the output power level to several watts. This leads to a large parasitic capacitance and the RC-limited bandwidth may become the dominant limiting factor of the speed of the high-power VCSEL array. In this work, Zn-diffusion and oxide-relief apertures are used to manipulate the optical modes and reduce the parasitic capacitance, respectively, in a unit device for a 940 nm VCSEL array. The demonstrated VCSEL array has a quasi-single-mode output, high available power (4 W; 1% duty cycle), narrow divergence angle (
∼
14
∘
at
1
/
e
2
) under maximum output power, and a fast rise time (
<
100
p
s
). These results open up new possibilities for further enhancing the performance of ToF sensing systems at the 940 nm wavelength.
Perovskite Quantum Dot LEDs. In their Communication on page 7924 ff., R. S. Liu et al. describe the generation of a white LED device through excitation of a silicone resin containing green mesoporous ...silica‐CsPbBr3 and red CsPb(Br0.4I0.6)3 perovskite quantum dots with a blue InGaN chip.
Inorganic perovskite quantum dots (IPQD) assisted by a yellow emitting YAG:Ce phosphor were integrated on a blue LED chip. The red perovskite quantum dot (R-PQD) assisted YAG:Ce phosphors exhibit ...warm white light with CCT (3328 K), high color rendering index (CRI 84.7) and a super high value of saturated red color component R9 as 96. The results demonstrate that the inorganic red perovskite quantum dot assisted yellow phosphor material may be a potential candidate for the generation of warm white light for indoor lighting applications.
This study conducts a comprehensive investigation of crustal seismic anisotropy over varied geological regimes of Taiwan. With a large amount of earthquake data, the lateral variation of seismic ...shear wave splitting (SWS) is fully examined in terms of crustal deformation process. As the well-known vigorous orogeny subjected to the Eurasian—Philippine plate collision, tectonic convergence of Taiwan is presumably propagating from east to west. The acquired SWS waveform data cover areas from the slightly deformed Western Plains to the intermediate-to-high metamorphic Western Foothills and central mountain ranges. By means of waveform cross-correlation, the SWS parameters—the fast-wave polarization orientation and delay time—infer that the mechanism of lithologic deformation of Taiwan convergence can be classified into two domains: the convergence-parallel laminating west of the Deformation Front and the convergence-perpendicular striking east of the Deformation Front. The convergence-parallel SWS measurement presents the internal fabrics consisting of microfractures subject to lateral compression before the yielding of the lithologic strength, whereas the convergence-perpendicular measurements reveal the lateral accommodation of deformation as the stress/strain surpass the yielding strength of rock, where the predominant SWS polarization is in the NE—SW direction similar to the general trend of Taiwan's mountain ranges. It is remarkable that there is no correlation between metamorphic degrees with SWS parameters. The geological province which corresponds to higher metamorphism is not consistent with large SWS parameters. This may be because of anisotropic weakness caused by multiple tectonic processes at considerable metamorphic zone. Furthermore, comparison of the SWS delay times with corresponding focal depths suggests that seismic anisotropy in the upper crust may come from multiple layers, and the fabric lamination causing the anisotropy may be confined only within the shallow crust.
In this study, we demonstrated a reliable technique combination a little phosphor and composite silica photonic crystals (c-SPhCs) for developing the candlelight light-emitting diodes (LEDs). We used ...a UV adhesive curing method for improving the adhesion properties of SPhCs. The warm-white LEDs with c-SPhCs exhibit a correlated color temperature of 2089 K, a color-rendering index of 80, and a luminous flux of 34.5 Im (5.4 times that of a candle). The LEDs were subjected to a reliability analysis (RA) test, applying a high temperature and high relative humidity (85 degreesC/85 RH) during operation current at 120 mA. During a RA test of 3300 h, no visible degradation in optical performance has been observed. We implemented a reliable and inexpensive technique for producing the residential lighting source.
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