High Internal Quantum Efficiency Research Articles

Engineering deep-red Al20B4O36:Cr3+ phosphors for photomorphogenesis

Cr3+ doped phosphors with deep-red luminescence hold great promise as artificial lighting sources for plants growth. Among them, α-Al2O3:Cr3+ is featured with an ultra-intense pure zero phonon line (ZPL) emission with negligible sidebands. Nonetheless, further enhancements in its luminescence thermal stability are required to fully unlock its potential for practical applications. To tackle this challenge, we propose that Al20B4O36 with a negative expansion coefficient could serve as a more favorable host materials for Cr3+ ion, thereby enhancing the luminescence thermal stability. Our first-principles calculations have unveiled similar electronic structures for α-Al2O3:Cr3+ and Al20B4O36:Cr3+, suggesting that the observed zero phonon R-line (2Eg) emission, arising from the 2Eg→4A2g transition in α-Al2O3:Cr3+, might also be present in Al20B4O36:Cr3+. Based on these findings, we prepared Al20B4O36:Cr3+ phosphors using a simple solid reaction method and confirmed that Al20B4O36:Cr3+ indeed exhibits a similar ultra-intense pure ZPL emission centered at 694 nm. Moreover, Al20B4O36:Cr3+ phosphors demonstrate remarkable properties including a high internal quantum efficiency (IQE) of 98.2 % and superior luminescence thermal stability compared to α-Al2O3:Cr3+. A phosphor converted light emitting diode (pc-LED) is developed by coating Al20B4O36:Cr3+ phosphor onto a near-ultraviolet LED chip. The lighting from this deep-red LED significantly impacts the photomorphogenesis of bean sprouts. Our study showcases a rational approach to design novel Cr3+ doped phosphors with enhanced luminescent properties, tailored for specific applications.

Spectroscopic properties and thermal stability of a Mn4+-doped polyfluoride phosphor for application in solid-state lighting

In this study, an efficient polyfluoride red-emitting phosphor, Cs3RbGe2F12:Mn4+ (denoted as CRGF:Mn), has been synthesized using a simple co-precipitation method. The crystal and electronic structures, spectroscopic properties, and photoluminescence thermal stability of CRGF:Mn have been systematically characterized. The results show that Mn4+ ions experience a strong crystal field and present a series of intense red emission peaks under blue light excitation. Moreover, CRGF:Mn exhibits a high color purity (95.1 %), high internal quantum efficiency (82.4 %), and enhanced photoluminescence thermal stability at 150 °C, with an intensity of 113 % relative to room temperature. A warm white light-emitting diode exhibiting a low correlated color temperature (3572 K), high color rendering index (90.7), and suitable luminous efficiency (132.6 lm/W) was prepared using CRGF:Mn as a red component, demonstrating viable application in solid-state lighting.

Full-visible-spectrum LED lighting by using a near-UV-excitable broadband blue-emitting Ca2LuHf2GaAl2O12:Ce3+ garnet phosphor

Highly efficient broadband blue-emitting phosphors are urgently needed for full-visible-spectrum white light-emitting diodes (WLEDs). Herein, we report a new highly luminescent garnet-type Ca2LuHf2GaAl2O12:Ce3+ (abbreviated as: CLHGAO:Ce3+) blue phosphor enabling full-visible-spectrum LED lighting. These CLHGAO:Ce3+ phosphors doped with different Ce3+ concentrations have been prepared by using a high-temperature solid-state reaction approach, and their phase purity, crystal structure, luminescent properties, CIE color coordinates, and quantum efficiency have been systematically studied. Importantly, CLHGAO:Ce3+ blue phosphors show a broadband excitation spectrum in the 300–450 nm spectral range peaking around 398 nm, matching well with the emission wavelengths of commercial near-ultraviolet LED chips (380–420 nm). Upon 398 nm excitation, the optimal CLHGAO:2%Ce3+ phosphor sample generates a bright broad blue emission band (emission peak: 472 nm; bandwidth: 84 nm) with high internal quantum efficiency of 79.2% and external quantum efficiency of 55.3%. Notably, the emission intensity of CLHGAO:2%Ce3+ phosphor is about 1.87 times higher compared to the commercial BaMgAl10O17:Eu2+ blue phosphor (emission peak: 451 nm; bandwidth: 53 nm). Finally, a white LED device is fabricated with a 395 nm near-UV LED chip with CLHGAO:2%Ce3+ blue phosphor and commercial (Ba,Sr)2SiO4:Eu2+ green phosphor as well as commercial CaAlSiN3:Eu2+ red phosphor, and the device demonstrates bright warm-white emission with an ultrahigh color rendering index (Ra = 95.1, R9 = 97.8, R12 = 88.4) and low correlated color temperature of 3540 K. These results show that as-developed blue-emitting CLHGAO:Ce3+ garnet phosphors with superior photoluminescence properties can potentially be used in phosphor-converted full-visible-spectrum WLEDs.

Urea-assisted combustion synthesis and nearly zero-thermal-quenching luminescence of highly efficient phosphate phosphor

Exploring green-emitting phosphors with high efficiency and thermostability is a significant issue for enhancing lighting and display quality. In this report, we adopted a facile urea-assisted combustion method to rapidly synthesize terbium-activated NaLaP4O12 (NLPO) powder with high crystallinity. The activators Tb3+ are incorporated into the NLPO lattice via equivalently replacing La3+ ions. Excited at 368 nm, it presents a bright green-emitting performance with high internal quantum efficiency, coming from the dominant 5D4→7F5 transitions of Tb3+. The green-emitting content quenching is controlled by the dipole–dipole interaction. Meanwhile, the emission in response to temperature reveals that the nearly zero-thermal-quenching is induced by the high activation energy barrier (0.31 eV) and suitable structure rigidity. Finally, the light emitting diodes are encapsulated using the studied material, manifesting that it would be a prospective green-emitting candidate. The research shows a guide for developing the terbium-activated phosphors with high luminescence efficiency and excellent thermostability.

Development of red phosphor Li8CaLa2Ta2O13:Eu3+ for WLEDs and anti-counterfeiting applications

A set of novel red phosphors Li8CaLa2Ta2O13:xEu3+ (LCLTO:xEu3+) were successfully prepared using a solid-state reaction method. The properties of the prepared samples, including phase purity, elemental composition, and morphology, were systematically investigated using X-ray diffraction, scanning electron microscopy, and diffuse reflectance spectroscopy analyses. The 610 nm maximum emission peak is attributed to the 5D0→7F2 transition of Eu3+ ion under 394 nm irradiation. Among all the LCLTO:xEu3+ phosphors, LCLTO:0.6Eu3+ showed the strongest emission intensity because of the concentration quenching effect of the electric dipole–dipole interaction among the Eu3+ ions, which was also demonstrated by the decay curves. Remarkably, the emission intensity of the optimal LCLTO:0.6Eu3+ phosphor, which exhibited a high internal quantum efficiency of 49.30% and excellent color purity of 96.79%, was approximately 2.29 times higher than that of commercial Y2O3:Eu3+ red phosphors. The thermal stability of the LCLTO:0.6Eu3+ sample with good color stability was meticulously investigated. The fabricated white-light-emitting diode (WLED) exhibited a superior color-rendering index of Ra = 82 and chromaticity coordinates of (0.3260, 0.3639), suggesting that LCLTO:0.6Eu3+ has potential applicability in developing efficient and high-quality WLEDs. Moreover, the prepared LCLTO:0.6Eu3+/PDMS composite film demonstrated exceptional flexural resistance and chemical stability, indicating considerable promise for practical anti-counterfeiting applications.

Cr3+‐Yb3+‐Ni2+ Tri‐Doped NIR Phosphors with Spectral Output Covering NIR‐I and NIR‐II Regions

AbstractTo realize efficient and broadband near infrared (NIR) light in both NIR‐I and NIR‐II regions, Gd3Mg0.5Al1.5Ga2.5Ge0.5O12 (GMAGG): Cr3+, Yb3+, Ni2+ phosphors are prepared in this study. The effects of Cr3+‐Yb3+ co‐doping and Cr3+‐Yb3+‐Ni2+ tri‐doping on the luminescence properties are investigated. GMAGG: Cr3+, Yb3+ exhibits high internal quantum efficiency (IQE) of 96.4%, and near‐zero thermal quenching (96.5%@423 K) in 650–1100 nm. By constructing energy transfer from Cr3+ to Ni2+, the emission range of GMAGG: Cr3+, Yb3+, Ni2+ is further extended to 650–1700 nm with a high IQE of 28% and good thermal stability (66%@423 K). The NIR LEDs prepared with GMAGG: 0.04Cr3+, 0.008Yb3+, and GMAGG: 0.04Cr3+, 0.008Yb3+, 0.04Ni2+ exhibit 57.5 and 8.1 mW at an input current of 100 mA, respectively. The results show that GMAGG: Cr3+, Yb3+, Ni2+ is a promising NIR phosphor for NIR light sources.

Cooperative cationic substitution strategy triggers high blue-light absorptance and near-infrared emission with high quantum efficiency in Cr3+-activated pyroxene-type assembly

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) assembled with the broadband NIR-emitting phosphors has been a promising light source for application in agricultural plant lighting, night vision, food analysis and medical diagnosis. But it suffers from a low photoelectric efficiency (<30 %) due to deficiency of phosphors with high internal quantum efficiency (IQE) and strong absorption capacity in the blue spectral region. Herein, a broadband NIR-emitting luminescent material capable of efficient blue to NIR light conversion with still high IQE was developed via the chemical-composition engineering of CaMgGe2O6:Cr3+ using cooperative cationic substitution of Ca2+-Mg2+ by Na + -Ga3+. The emission profiles evolved a red-shift from 839 to 859 nm with the full width at half-maximum (FWHM) extending from 161 nm to 177 nm as the increase of [Na+-Ga3+] pairs. In addition, the IQE can be finely adjusted. Importantly, the blue-light absorption efficiency can be greatly improved to 34.8 % upon pumping by the constant excitation energy. The increased local structural distortion induced by introducing [Na+-Ga3+] pairs has been verified for the main factor causing these desirable optical properties change. Benefiting from the improvement of blue-light absorptance, the fabricated NIR pc-LED device via coating the developed phosphor on a blue LED chip achieved the larger photoelectric efficiency 31.2 %@10 mA compared to the previously reported value of 27.2 %@10 mA. The excellent performance of biomedical imaging and night vision surveillance represented by the assembled NIR pc-LED was demonstrated.

Modeling polarization effects on internal quantum efficiency of micro-LEDs at low current density

This study investigates the optoelectronic properties of blue micro-light-emitting diodes (µ-LEDs) by modeling the semipolar single quantum well (QW) at low current density. Through simulation analyses, the influences of the eight selected crystal orientations and different QW thicknesses on the internal quantum efficiency (IQE) and forward voltage are investigated for low current density LEDs. The simulation results of the energy band diagram show that reversed polarization increases the band tilt in the same direction as the built-in electric field, resulting in IQE poorer than that of LEDs whose polarization is of the same magnitude but positive. However, reversed polarization also reduces the hole barrier height, resulting in lower forward voltage at the same current density. Finally, it is found that weakly positive-polarized (101̄2) LEDs have the highest IQE and maximum allowed thickness at low current density, which is due to the flat energy band with a reduced band tilt caused by weakly positive polarization.

Tunable bandgap and Si-doping in N-polar AlGaN on C-face 4H-SiC via molecular beam epitaxy

N-polar AlGaN is an emerging wide-bandgap semiconductor for next-generation high electron mobility transistors and ultraviolet light emitting diodes and lasers. Here, we demonstrate the growth and characterization of high-quality N-polar AlGaN films on C-face 4H-silicon carbide (SiC) substrates by molecular beam epitaxy. On optimization of the growth conditions, N-polar AlGaN films exhibit a crack free, atomically smooth surface (rms roughness ∼ 0.9 nm), and high crystal quality with low density of defects and dislocations. The N-polar crystallographic orientation of the epitaxially grown AlGaN film is unambiguously confirmed by wet chemical etching. We demonstrate precise compositional tunability of the N-polar AlGaN films over a wide range of Al content and a high internal quantum efficiency ∼74% for the 65% Al content AlGaN film at room temperature. Furthermore, controllable silicon (Si) doping in high Al content (65%) N-polar AlGaN films has been demonstrated with the highest mobility value ∼65 cm2/V-s observed corresponding to an electron concentration of 1.1 × 1017 cm−3, whereas a relatively high mobility value of 18 cm2/V-s is sustained for an electron concentration of 3.2 × 1019 cm−3, with an exceptionally low resistivity value of 0.009 Ω·cm. The polarity-controlled epitaxy of AlGaN on SiC presents a viable approach for achieving high-quality N-polar III-nitride semiconductors that can be harnessed for a wide range of emerging electronic and optoelectronic device applications.

Achieving atomically ordered GaN/AlN quantum heterostructures: The role of surface polarity.

Interface engineering in heterostructures at the atomic scale has been a central research focus of nanoscale and quantum material science. Despite its paramount importance, the achievement of atomically ordered heterointerfaces has been severely limited by the strong diffusive feature of interfacial atoms in heterostructures. In this work, we first report a strong dependence of interfacial diffusion on the surface polarity. Near-perfect quantum interfaces can be readily synthesized on the semipolar plane instead of the conventional c-plane of GaN/AlN heterostructures. The chemical bonding configurations on the semipolar plane can significantly suppress the cation substitution process as evidenced by first-principles calculations, which leads to an atomically sharp interface. Moreover, the surface polarity of GaN/AlN can be readily controlled by varying the strain relaxation process in core-shell nanostructures. The obtained extremely confined, interdiffusion-free ultrathin GaN quantum wells exhibit a high internal quantum efficiency of ~75%. Deep ultraviolet light-emitting diodes are fabricated utilizing a scalable and robust method and the electroluminescence emission is nearly free of the quantum-confined Stark effect, which is significant for ultrastable device operation. The presented work shows a vital path for achieving atomically ordered quantum heterostructures for III-nitrides as well as other polar materials such as III-arsenides, perovskites, etc.

Emission modulation of Eu3+ via symmetry around dodecahedron in garnet-type Ca2EuZr2-xSnxGa3O12 (x = 0, 0.5, 1, 1.5, and 2) phosphors

White LEDs offer advantages such as high efficiency and a long lifetime. However, their color rendering index is low due to the lack of red components. Herein, we synthesized new garnet-type Ca2EuZr2-xSnxGa3O12 (x = 0, 0.5, 1, 1.5, and 2) phosphors via a solid-state reaction. These phosphors exhibited red emission under ultraviolet excitation at 395 nm and a high internal quantum efficiency (>45 %) in all samples. In addition, the intensity of the emission of the 5D0→7F4 transition (∼710 nm) increased with an increase in the x value. We also explored the relationship between the intensity of the 5D0→7F4 transition and the symmetry around Eu3+. Doping Sn4+ into the garnet-type Ca2EuZr2-xSnxGa3O12 phosphors increased the length of the shared edge between the tetrahedra and dodecahedra in the garnet-type structure. Consequently, the geometry of the dodecahedra approached that of a square antiprism-like polyhedron, which in turn affected the 5D0→7F4 transition of Eu3+.

Improved thermal stability and quantum efficiency of novel cyan phosphors toward full-visible-spectrum lighting

Highly efficient cyan phosphors have been identified as essential components in addressing the cyan gap present in the emission spectra of traditional white light emitting diodes. Here, we report novel Ba4Ca1-yLay(PO4)3Cl:Eu2+ (y = 0–0.15) phosphors with broadband cyan emission based on an efficient and positive cationic heterovalent substitution strategy. Under the near ultraviolet excitation, the quantum yield and thermal stability are progressively enhanced by introducing La3+ to replace the Ca2+ ions, owing to the band gap and killer centers engineering. The Ba3.92Ca0.9La0.1(PO4)3Cl:0.08Eu2+ phosphor exhibits a pronounced emission band in the cyan-green spectral range with a high internal quantum efficiency of 88.0% and an impressive external quantum efficiency of 72.1%. The utilization of Ba3.92Ca0.9La0.1(PO4)3Cl:0.08Eu2+ as the cyan emitting component in the fabrication of white light-emitting diode (WLED) has demonstrated remarkable advancements in the color rendering index value, emphasizing the potential of these phosphors for future implementation in the next generation full-visible-spectrum WLED lighting. Our findings offer evidences that defect engineering techniques effectively enhance the performance of light-emitting diode (LED) phosphors.

Simultaneous enhancement of red luminescence and thermal stability of a novel red phosphor: A Li+-Eu3+ co-occupied site strategy in BaAl2Ge2O8 lattices

The rapid development of phosphor-converted white light emitting diodes (pc-WLEDs) requires new red phosphors with efficient and thermally stable luminescence for high-quality warm-white lighting. However, it is still a challenge to discover red phosphors with facile synthesis, high internal quantum efficiency (IQE), excellent thermal stability and high color purity. Herein, a novel red-emitting Eu3+ activated barium dialuminum digermanate (BaAl2Ge2O8, BAGO) phosphor showing strong red emission at 610 nm was prepared. The IQE is improved from 32.91% to 78.84% by employing a charge compensation strategy. The lithium-ion co-doped BAGO:Eu3+ phosphor exhibits a nearly twofold increase in integral photoluminescence (PL) intensity and the high color purity reaches 94.17%. Impressively, the PL intensity of the BAGO:Eu3+,Li+ phosphor drops by only 2.6% at 150 °C of that at room temperature. Finally, the pc-WLED using the red BAGO:Eu3+,Li+ phosphor exhibits white light with the chromaticity coordinate of (0.3515, 0.3495), a high color-rendering index of 92 and a low correlated color temperature of 4746 K. All these results manifest that BAGO:Eu3+,Li+ phosphor is a suitable red phosphor for near-ultraviolet (NUV) chip-based pc-WLEDs.

Valence conversion and site reconstruction in near-infrared-emitting chromium-activated garnet for simultaneous enhancement of quantum efficiency and thermal stability

Achievement of high photoluminescence quantum efficiency and thermal stability is challenging for near-infrared (NIR)-emitting phosphors. Here, we designed a “kill two birds with one stone” strategy to simultaneously improve quantum efficiency and thermal stability of the NIR-emitting Ca3Y2-2x(ZnZr)xGe3O12:Cr garnet system by chemical unit cosubstitution, and revealed universal structure-property relationship and the luminescence optimization mechanism. The cosubstitution of [Zn2+–Zr4+] for [Y3+–Y3+] played a critical role as reductant to promote the valence transformation from Cr4+ to Cr3+, resulting from the reconstruction of octahedral sites for Cr3+. The introduction of [Zn2+–Zr4+] unit also contributed to a rigid crystal structure. These two aspects together realized the high internal quantum efficiency of 96% and excellent thermal stability of 89%@423 K. Moreover, information encryption with “burning after reading” was achieved based on different chemical resistance of the phosphors to acid. The developed NIR-emitting phosphor-converted light-emitting diode demonstrated promising applications in bio-tissue imaging and night vision. This work provides a new perspective for developing high-performance NIR-emitting phosphor materials.

Mechanistic Insight into the Defect-Engineered White Light Emission from the Single-Phase Orthovanadate Phosphor Synthesized by a Facile Rapid Microwave-Assisted Synthesis.

The synthesis of single-phase barium orthovanadate phosphors by a one-pot microwave-assisted hydrothermal approach has been reported, wherein the homogeneous thermal zone generated at the molecular level by microwave radiation gives rise to tunable distortion in the tetrahedral VO4-3 and oxygen vacancies, eventually enabling intrinsic white light emission with CIE of 0.31,0.38, high photoluminescence internal quantum efficiency of 35%, and external quantum efficiency of 28% whereas phosphor synthesized by the hydrothermal route exhibits only bluish-green emission (PLQE: 0.5%). The Rietveld refinement confirms the formation of a single trigonal phase having dissimilar V-O bond lengths and bond angles, implying the formation of a distorted phosphor under optimized conditions, and corroborates with Raman and Fourier transform infrared analyses. The X-ray photoelectron spectroscopy and electron paramagnetic resonance analysis reveal that the origin of white light emission is due to short- and long-range defects, in particular the oxygen vacancies, which eventually form an intermediate energy level in the forbidden region between the valence and conduction bands. Lifetime spectra show triexponential fitting, corresponding to two charge transfer blue and green emission bands (3T2, 3T1 to 1A1) and one oxygen vacancy-related red emission at RT. Furthermore, these phosphors are thermally stable, as no change in the structure or emission characteristics are observed. A prototype fabricated using a 365 nm chip exhibits white-light-emission CIE of 0.353,0.392, correlated color temperature of 4867 K, color rendering index of 85, and high luminous efficacy of 102 lm/W at 140 mA operating current, portentous for practical applications.

Highly efficient and stable Cr3+-activated oxyfluoride near-infrared emitting phosphor for night vision and plant growth

Near-infrared (NIR) light sources have many potential applications in biological, night vision, food safety, and plant growth. In this study, we report a highly efficient and thermally stable NIR phosphor LiAl4(1-x)O6F:xCr3+ (in brief LAOF:Cr3+). Under 565 nm excitation, the optimal LAOF:1.1%Cr3+ phosphor shows two sharp line spectra (named Cr1) centered at 703 nm and 713 nm, and a broadband emission (named Cr2) centered at 770 nm, which is ascribed to the [AlO6] and [Al(O, F)6] octahedra in the LAOF structure. Its unique narrowband and broadband emission correspond well with the absorption band of far-red phytochrome pigments (PFR), suggesting the potential application in plant growth. The FWHM extends from 25 to 53 nm as rising the Cr3+ ions concentration, and the Cr2 emission becomes more and more conspicuous. The LAOF:1.1%Cr3+ phosphor exhibits a high internal quantum efficiency (IQE) and external quantum efficiency (EQE) of ∼83.0% and 36.4%, respectively. Moreover, the LAOF:1.1%Cr3+ phosphor has good thermal stability (84.3%@373 K). NIR pc-LED device manufactured with a 450 nm blue LED chip and LAOF:1.1%Cr3+ phosphor exhibits good NIR output power (31.07 mW@100 mA) and photoelectric efficiency (13.3%@10 mA). The findings suggest the LAOF:Cr3+ phosphor holds potential in NIR pc-LED applications.

A strategy for designing temperature-sensitive complexes based on ligand vibration rotation mode control

Copper(I) and 3,5-dimethyl-1,2,4-triazole ligands construct the isomers α-Cu(mdtz) and β-Cu(mdtz), respectively. In α-Cu(mdtz), the hexagonal ring structure composed of Cu(I) and N atoms restricts the vibrational rotation of the triazole ring structure and reduces the nonradiative transition, achieving a high internal quantum efficiency at room temperature and pressure (IQY = 72.3%). As for β-Cu(mdtz), the triazole ring can rotate back and forth along its own C2 axis within a certain angle. We investigated the comparison of the luminescence spectra of α-Cu(mdtz) and β-Cu(mdtz) at different temperatures, confirmed that the vibrational rotation of the triazole ring improved the sensitivity of the luminescence intensity and spectral broadening to the temperature response, especially at low temperatures. In addition, we found that the decay time of Cu(mdtz)s varies linearly with temperature in a certain temperature interval, which provides strategy for temperature measurement based on the luminescence lifetime. Besides, the non-porous structure of Cu(mdtz)s prevents oxygen from entering the structure and protects the luminescent center from oxygen, thus improving the accuracy of temperature measurement in atmospheric environments.

Zero thermal quenching and suppressed concentration quenching in a highly efficient structure‐confined fluoride near-infrared phosphor

The development of thermally stable and efficient broadband near-infrared (NIR) phosphors suffers from severe hindrance. Herein, a unique anti-fluorescence quenching is realized in a novel Cs2NaGaF6: Cr3+ NIR fluoride phosphor with a strategy of integrating the structural confinement effect with weak electron-phonon coupling effect. Upon blue light excitation, this phosphor exhibits a wide emission band with a peak wavelength of ∼789 nm and a full width at half maximum (FWHM) of 117 nm. Thanks to the structural confinement effect, a large quenching content of 20 mol% and a high internal quantum efficiency (IQE) of 87.4% are achieved, showing a suppressed concentration quenching behavior. Significantly, Cs2NaGaF6: 0.20Cr3+ phosphor possesses an abnormal zero thermal quenching, which could be related with the weaker electron-phonon coupling effect. The emission intensity of Cs2NaGaF6: 0.20Cr3+ at 423 K can maintain up to 101.96% of that at 298 K. A fabricated NIR phosphor-converted light-emitting diode (pc-LED) exhibits an output power of 57.71 mW and a photoelectric conversion efficiency as high as 19.24% at 100 mA. Finally, utilizing a high-power NIR LED as the illuminant for traffic surveillance, significant information can be captured even in low-visibility environments. As a result, Cs2NaGaF6: Cr3+ possesses tremendous prospects in high-power NIR LEDs.

Wafer-scale heteroepitaxy GaN film free of high-density dislocation region with hexagonal 3D serpentine mask

GaN-based III-Nitride compound semiconductors are fundamental materials for high-performance optoelectronic and electronic devices. Low-defect-density substrate has been a major bottleneck in achieving high internal quantum efficiency and high breakdown voltage in those devices. However, a large-scale and uniform low dislocation density GaN film is still hard to obtain on foreign substrates, which is the mainstream economical method in scientific research and industrial production. Here, we present a 3D serpentine mask method of growing high-quality GaN film on foreign substrates without high dislocation density (HDD) areas by designing both sectional and planar shapes of stacked masks. The serpentine channel in the cross-section mechanically blocks the extended dislocations and the hexagonal planar pattern reduces the dimension of coalescence geometry. A wafer-scale GaN epilayer, free of HDD zone, with the overall threading dislocation density of 1.7 × 107 cm−2 estimated by plan-view cathode luminescence, is achieved in the metal-organic chemical vapor deposition system. Then, an array of light-emitting diodes based on this substrate with low forward voltages and high light output powers are fabricated, which introduces a practical method to provide high-quality GaN films for high-performance optoelectronic devices.

Preparation and Optical Property of Far-Red LED Encapsulated with the Graded-Index Fluorescent Glass Film

Fabricating far-red light-emitting diodes (LEDs) with high emission efficiency is a change for the application in plant growth. In this work, a new type of far-red LED was fabricated for plant growth by encapsulating the Sr3LiSbO6:Mn4+, Mg2+ (SLSO:Mn4+, Mg2+) far-red phosphors with the gradient-refractive glass films. Under 365 nm excitation, the phosphors emitted the wide band in the 550–800 nm range, which overlapped with the absorption band of plants that absorb far-red light (PFR). The internal quantum efficiency (IQE) of the LED was 93.6%. Compared with the luminous efficacy of traditional (fluorescent silicone) LEDs (59 lm/W), the luminous efficacy of the new LED is increased by 62.7%, and reaches 96.74 lm/W. Thus, this far-red LED with high IQE has a long-term application prospect in plant growth.