Near-ultraviolet Research Articles

Photoluminescence properties of wet-chemically synthesized Tb3+ and Sm3+doped K3Ca2(SO4)3Cl phosphor

In this study, we are successfully synthesized terbium and samarium (Tb3+/Sm3+) doped K3Ca2(SO4)3Cl phosphors by wet chemical method, and synthesized phosphors were characterized by XRD, SEM, and Photoluminescence (PL) techniques, and studied in detail. Photoluminescence analysis, we can see that under the Near-UV (NUV) excitation of 380nm, the Tb3+ activated samples showed a prominent green emission peak at 546nm attributed to the 5D4→7F5 transition of Tb3+ions. While the PL emission spectra of 404 nm light excited K3Ca2(SO4)3Cl:Sm3+phosphorshowedthree emission lines at 565nm, 598nm and 645nm attributed to 4G5/2→6H5/2, 4G5/2→6H7/2, and4G5/2→6H9/2 transitions of Sm3+ ions, respectively. The CIE coordinates were calculated to be (0.263, 0.515) for K3Ca2(SO4)3Cl:Tb3+and (0.532, 0.462) for K3Ca2(SO4)3Cl: 1.5mol%Sm3+, which liedin the green and orange regions, respectively. The entire photoluminescence results indicated that phosphor K3Ca2(SO4)3Cl doped with Tb3+ and Sm 3+may turn out to be an important component of pc-white LEDs and display devices.

Radiation stability and photothermal performance of surface-functionalized plasmonic nanofluids for direct-absorption solar applications

In this work, the photostability of gold nanoparticles (AuNPs) with different functional molecular coatings was investigated. Gold/water nanofluids were prepared using citrate (CIT) reduction, then coated with polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), or bovine serum albumin (BSA) by physical/chemical ligand adsorption. All nanofluids retained their monodispersity and extinction efficiency after ambient storage for three years. These long-term aged nanofluids were then subjected to accelerated indoor tests that mimic the prolonged and cyclic exposure to both full-spectrum and specific-band radiation. This included continuous exposure to broadband solar radiation at various intensities and focused near-ultraviolet (NUV) radiation for different durations, as well as cyclic exposure (in irradiation/darkening periods) to both solar and NUV radiation. Assessment of post-test stability has been realized using complementary characterization techniques. Results showed that stability was variable to the coating type, radiation exposure mode, and radiation spectrum. Subtle physicochemical transitions in the polymeric coatings, even in the absence of ligand desorption and particle clustering, were shown to alter the optical properties and wettability of the nanofluids. While the gold cores remained intact, some photoinduced instabilities occurred in the adsorbed polymeric coatings, including chain scission of PEG, conformational collapse of PVP, and partial denaturation of BSA. Largely attributed to the strong polymer-Au interactions and high surface grafting densities, and despite their coating transformations, AuNPs maintained a high level of photostability. This work marks important progress towards realizing photothermally superior, yet colloidally stable, solar nanofluids compatible with a wide range of direct-absorption photothermal applications in the water and energy sectors. • Plasmonic gold nanoparticles stabilized using different polymeric coatings. • Accelerated radiation stability tests mimicking continuous/cyclic solar/UV exposure. • Insight gained into photoinduced physiochemical transitions in cores and coatings. • Stability variable to coating type, radiation exposure mode, and radiation spectrum. • Photostability limitations elucidated for photothermal conversion applications.

High-performance red@green core-shell emitting nitride phosphor with monodisperse Eu2+ luminescence centers for solid state lighting

The red@green core-shell emitting phosphor with monodisperse luminescence center was successfully constructed by Eu2+ doped Sr2Si5N8 and Sr2Si5N8@SrSi2O2N2 via a deposition-precipitation (DP) method. Compared to traditional solid state reaction (SSR) method, under excitation at 370 nm, Sr2Si5N8:0.05Eu2+ phosphor prepared by DP method exhibits red emission at 611 nm and an ~1.4-fold luminescent intensity enhancement. Interestingly, upon near-ultraviolet (NUV) excitation, Eu2+ doped Sr2Si5N8@SrSi2O2N2 phosphors prepared by DP method exhibit a dual emission feature with the green emission at 538 nm and red emission peak at 611 nm. The elemental line scanning spectrum of the energy dispersive X-ray analysis indicates a core@shell structure of Sr2Si5N8@SrSi2O2N2. Furthermore, this red@green core-shell emitting phosphor can be encapsulated in ultra-low melting Sn-F-P-O glass to achieve the white light with excellent color quality Ra = 85) and low correlated color temperature (4484 K) when pumped by near ultraviolet LED chips.

Desired warm white light emission from a highly photostable and single-component Gd2TiO5:Dy3+/Eu3+ nanophosphors for indoor illuminations

At present, phosphor-converted white light-emitting diodes (pc-WLEDs), developed by combining an ultraviolet (UV)/near-UV (NUV) LED and a single-component white emitting phosphor, have attracted significant interest and are emerged as the new-generation green light sources. Herein, we report a highly photostable and novel Gd2TiO5 (GT):Dy3+/Eu3+ nanophosphors as single-component white emitting phosphors by sol-gel route. Based on X-ray diffraction pattern, Rietveld refinement is performed to authorize the orthorhombic phase of the GT nanophosphors. The nanosized particles with nearly spherical morphology is perceived after annealing at 1100 ℃. The Dy3+ and Eu3+ ions individually-doped GT nanophosphors exhibited pleasant white and reddish-orange emissions by monitoring with their respective excitation wavelengths. Tunable white light emission is achieved by co-doping the various concentrations of Eu3+ ions to the optimized GT:1.5Dy3+ nanophosphors under both UV (270 nm) and NUV (362 nm) excitations. The energy transfer probability is discussed and the energy transfer efficiency from Dy3+ to Eu3+ ions is calculated from the luminescence decay profiles. On rising the Eu3+ ions content from 0.25 to 6 mol%, the energy transfer efficiency is increased from 14% to 73% for co-doped GT nanophosphors. Besides, the optimized samples of Dy3+ and Eu3+ ions individually-doped and co-doped GT samples exhibited high quantum efficiencies and increased photostability. Thus, the acquired results signifying that these GT:Dy3+/Eu3+ nanophosphors can serve as potential single-component white emitting phosphors for UV and/or NUV-based pc-WLEDs.

Near-UV and near-IR reflectance studies of lunar swirls: Implications for nanosize iron content and the nature of anomalous space weathering

We performed an analysis of spacecraft multispectral images for lunar swirls in order to gain an improved understanding of optical space weathering on the Moon and its causes. LROC WAC data provide information on the slope of the spectrum in the near-UV (NUV), as measured by the 321-nm/415-nm or 321-nm/360-nm reflectance ratios. Kaguya MI data were used to assess the near-infrared (NIR) continuum slope (1548-nm/749-nm reflectance ratio). Context for interpreting the spectral variations found in the remotely observed regions of the lunar surface is provided by laboratory reflectance spectra of lunar rocks and soils, as well as spectra for transparent silica gel analogs (Noble et al., 2007) containing different sizes and abundances of nanometer-sized iron (nsFe) particles. We gain additional insights into the spectral effects of sample maturity by considering the ferromagnetic resonance parameter (Is) values for mare and highland soils, as well as the number density of nsFe particles in the silica gels.We examined a set of three mare swirls (Reiner Gamma, Ingenii, and Mare Marginis) and three highland swirls (Airy, Descartes, and Gerasimovich). The NIR continuum slopes of both mare and highland swirls are shallower than those of the nearby normal mature regolith. Bright swirl surfaces have higher NIR slopes than normal fresh material of the same albedo. The NUV ratios within mare swirls are lower than in the mature background, but for highland swirls, the NUV ratios are approximately the same as the mature background. We do not see definitive evidence for "over-maturation" (excessive darkening and reddening beyond that found in the normal background surfaces) in dark lanes at the swirls we examined, although saturation of weathering effects at a high-iron location like Reiner Gamma could prevent over-maturation from appearing – even if enhanced solar-wind bombardment related to deflection by local magnetic fields is taking place.Evaluation of the NIR character of swirls and comparison with lab spectra of lunar soils and nsFe-bearing silica gel analogs leads to the conclusion that swirl materials contain abundances of nsFe that are lower than that of normal non-swirl background surfaces; the nsFe content of swirls corresponds to immature (though not pristine) or submature soils. However, the size distribution of nsFe in swirls is anomalous compared with normal lunar surfaces, with a deficiency in the smaller size range (< ~15 nm), as inferred from the NUV character of swirls. Because the flux of solar-wind ions reaching the surface in swirls is attenuated by shielding by crustal magnetic fields, we conclude that solar-wind exposure is the primary agent for production of small nsFe in normal lunar space weathering. Micrometeoroid bombardment, which is unimpeded by the presence of magnetic fields, is mainly responsible for production of larger nsFe in space weathering.

MoS2 Based Photodetectors: A Review.

Photodetectors based on transition metal dichalcogenides (TMDs) have been widely reported in the literature and molybdenum disulfide (MoS2) has been the most extensively explored for photodetection applications. The properties of MoS2, such as direct band gap transition in low dimensional structures, strong light–matter interaction and good carrier mobility, combined with the possibility of fabricating thin MoS2 films, have attracted interest for this material in the field of optoelectronics. In this work, MoS2-based photodetectors are reviewed in terms of their main performance metrics, namely responsivity, detectivity, response time and dark current. Although neat MoS2-based detectors already show remarkable characteristics in the visible spectral range, MoS2 can be advantageously coupled with other materials to further improve the detector performance Nanoparticles (NPs) and quantum dots (QDs) have been exploited in combination with MoS2 to boost the response of the devices in the near ultraviolet (NUV) and infrared (IR) spectral range. Moreover, heterostructures with different materials (e.g., other TMDs, Graphene) can speed up the response of the photodetectors through the creation of built-in electric fields and the faster transport of charge carriers. Finally, in order to enhance the stability of the devices, perovskites have been exploited both as passivation layers and as electron reservoirs.

Comparative Evaluation of Dual Emission Mode for Yellowish-Green Borophosphate-Based Solid Solution La &lt;sub&gt;7&lt;/sub&gt;O &lt;sub&gt;6&lt;/sub&gt;(BO &lt;sub&gt;3&lt;/sub&gt;)(PO &lt;sub&gt;4&lt;/sub&gt;) &lt;sub&gt;2&lt;/sub&gt;:Er

To acquire visible emissions using near-ultraviolet (NUV) and near-infrared (NIR) irradiations for multiple solid state lighting and display applications, exploring efficient upconversion (UC)/downconversion (DC) mode of erbium ion in different matrixes is of great importance. Here, we aimed to originally study the dual emission mode of borophosphate La7O6(BO3)(PO4)2 (LBP)-based solid solution doped with erbium ion. Er3+ occupies the lattice site of La3+ . A yellowish-green light is acquired by both DC and UC. It is identified that the UC photoluminescence has lower correlated color temperature (5694 K), higher color purity (87%), and longer lifetime (0.338 ms) than the DC. The present research can provide a new insight into the design and UC/DC photoluminescence of borophosphate-based solid solution fabricated by erbium for expanding solid state lighting applications.

Carbon dots optimize the luminescence and morphological of Tm3+ doped zinc borate composites for NUV-WLEDs

Rare earth (RE)-doped luminescent materials have shown tremendous potential applications in the optical field. However, it is still a challenge to improve its luminescence properties further. In this study, the Tm3+-doped zinc borate (4ZnO·B2O3·H2O, ZBH) with a flaky-like morphology was successfully prepared by a facile hydrothermal reaction. The photoluminescence (PL) performance of ZBH:Tm3+ is improved through incorporating yellow N-doped carbon dots (yNCDs). Simultaneously, by changing the content of yNCDs in ZBH:Tm3+ host, the morphological evolution from flaky-like to flower-like of the ZBH:Tm3+/yNCDs composite are realized. The ZBH:Tm3+/yNCDs composite with flower-like exhibits the strongest white light emission and splendid thermal stability under 360 nm excitation wavelength, matching the current mainstream near-ultraviolet (NUV) LED chip. Thus, ZBH:Tm3+/yNCDs composite might be a promising luminescent material in the NUV white lighting and display fields. The findings of this study developed a novel idea for improving the luminescent properties of RE-doped materials. Besides, it also solves fluorescence quenching problems of carbon dots in the solid-state illumination field.

Crystal structure and photoluminescent analysis of bright orange-red emanating Sm3+-doped Ca9Bi(VO4)7 nanophosphor for WLEDs

A bright orange-red emanating Ca9Bi1−x(VO4)7:xSm3+ (x = 0.05–0.5) nanophosphor crystalline series has been synthesized for the first time through solution combustion route. X-ray diffraction pattern of Ca9Bi0.80Sm0.20(VO4)7 was analyzed and processed using Rietveld Refinement. The nanophosphors synthesized were found to crystallize in trigonal crystal lattice with R3c(161) space group. The morphological behavior of prepared nanophosphors was studied by means of transmission electron microscopy (TEM). The photoluminescence nature of the nanophosphors corresponds to bright orange emission due to near-ultraviolet (NUV) excitation at 405 nm followed by 4G5/2 → 6H7/2 radiative relaxation. The chromaticity coordinates (x = 0.5504, y = 0.4484) are in harmony with the intense orange-red emission. The decay curves been well fitted in 1st-order exponential decay function indicate that a single type of crystallographic site is occupied by the dopant-Sm3+ ions in host lattice. Auzel’s model was implemented to investigate into rates of nonradiative relaxation (302.008 s−1), radiative lifetime (0.76 ms), and quantum efficiency (81%) values. The crystalline and optical behavior of the synthesized orange-red emitting nanophosphors promote their usage in near UV-based WLEDS.

Light wavelength and intensity effects on larval settlement in the Pacific oyster Magallana gigas

Oyster larvae initially have an eyespot on settlement stage (pediveligers). This study investigated the eyespot with light wavelength-dependent absorbance, and its functional details for settlement in the Pacific oyster Magallana gigas larvae. Eyespot efficiently absorbed 500–650 nm of light wavelength. Based on the eyespot absorbance, pediveligers were subjected to different light conditions with light-emitting diodes (LEDs): near ultraviolet (NUV), blue, white, green, red, and near infrared (NIR), set at 3 intensities (5, 15, 25 W/m2, except for NIR, which was at 25, 50, 100 lux). LEDs modulated at each intensity were continuously irradiated for 2 days, and the number of settled larvae on a substrate of shell chips was counted daily. NUV at 15, 25 W/m2, and white and green light at 5, 15 W/m2 disrupted larval settlement, whereas red at 25 W/m2 and NIR at 100 lux showed strong settlement-inducing activities. Red and NIR were further tested with ceramic paper substrates; inert substrates. These lights maintained their performance, with settlement rates higher than controls in darkness. Our findings contribute to the further understanding of the function of eyespot in the settlement of oyster larvae, and to establish criteria to evaluate light pollution levels for protecting benthic ecosystem.

Eu2+-doped microporous aluminosilicate Ca-chabazite Ca1.9Al3.8Si8.2O24 phosphor: synthesis and characterization of potential blue phosphor for NUV wLED

Near-UV (NUV)-excitable blue-light-emitting Eu2+ ions-doped Ca-chabazite Ca1.9Al3.8Si8.2O24 phosphor was synthesized by facile urea-assisted combustion synthesis method. Prepared materials were characterized by X-ray diffraction (XRD) study, scanning Electron Microscopy (SEM), and photoluminescence (PL) spectroscopy. The Eu2+-doped Ca1.9Al3.8Si8.2O24 calcium aluminosilicate phosphor exhibited intense and broad emission in the blue region. CIE chromaticity coordinates were plotted and obtained values were compared with standard NTSC coordinates. Electron vibration interaction (EVI) parameters such as Huang Rhy’s factor (S) and effective phonon energy (ħω) were calculated to determine the strength of electron–phonon coupling. The prepared mineral-based blue-emitting Near-UV-excitable phosphor may prove to be a potential candidate as a blue component for the white light emitting diode (wLED).

SN 2017hpa: a carbon-rich Type Ia supernova

ABSTRACT We present the optical (UBVRI) and ultraviolet (Swift-Ultraviolet and Optical Telescope) photometry, and optical spectroscopy of Type Ia supernova SN 2017hpa. We study broad-band ultraviolet (UV)+optical light curves and low-resolution spectroscopy spanning from −13.8 to +108 d from the maximum light in B band. The photometric analysis indicates that SN 2017hpa is a normal Type Ia supernova with ΔmB(15) = 0.98 ± 0.16 mag and MB = −19.45 ± 0.15 mag at a distance modulus of μ = 34.08 ± 0.09 mag. The (uvw1 − uvv) colour evolution shows that SN 2017hpa falls in the near-UV (NUV)-blue group. The (B − V) colour at maximum is bluer in comparison to normal Type Ia supernovae. Spectroscopic analysis shows that the Si ii λ6355 Å absorption feature evolves rapidly with a velocity gradient, $\dot{v}=128\pm 7$ km s−1 d−1. The pre-maximum phase spectra show prominent C ii λ6580 Å absorption feature. The C ii 6580 Å line velocity measured from the observed spectra is lower than the velocity of Si ii λ6355 Å, which could be due to a line-of-sight effect. The synthetic spectral fits to the pre-maximum spectra using syn++ indicate the presence of a high-velocity component in the Si ii absorption, in addition to a photospheric component. Fitting the observed spectrum with the spectral synthesis code tardis, the mass of unburned C in the ejecta is estimated to be ∼0.019 M⊙. The peak bolometric luminosity is $L^{\rm {bol}}_{\rm {peak}} = 1.43\times 10^{43}$ erg s−1. The radiation diffusion model fit to the bolometric light curve indicates 0.61 ± 0.02 M⊙ of 56Ni is synthesized in the explosion.

Near-Ultraviolet Transparent Organic Hole-Transporting Materials Containing Partially Oxygen-Bridged Triphenylamine Skeletons for Efficient Perovskite Solar Cells

Organic semiconducting materials that are optically transparent in the near-ultraviolet (NUV) region from 300 to 400 nm are needed for advanced perovskite devices such as bifacial semitransparent a...

Sr3Lu (VO4)3: Eu3+ red‐emitting phosphors for warm white LEDs

AbstractA series of novel red emission phosphors Sr3Lu1‐x(VO4)3:xEu3+(x = 0.007, 0.009, 0.02, 0.04, 0.06) were synthesized successfully by traditional high‐temperature solid‐state reaction. The results of X‐ray diffraction (XRD) reveal the doped Eu3+ ions have replaced the lattice sites of Lu3+ ions. The diffuse reflectance spectra illustrate the energy gap of Sr3Lu(VO4)3 host is 3.61 eV. The room‐temperature steady‐state fluorescence spectra show that these phosphors can be effectively pumped by the charge‐transfer band (CTB) of the host in near ultraviolet (NUV) spectral region and then produce strong and pure red emission at 615 nm originated from 5D0 → 7F2 electric dipole transition of Eu3+. The Commission Internationale de L’Eclairage (CIE) coordinates of Sr3Lu0.96(VO4)3:0.04Eu3+ are (x = 0.65, y = 0.35), which are very close to the red standard of National Television Standards Committee NTSC (0.67, 0.33). The fabricated warm white‐light‐emitting diodes (LED) demonstrate high color‐rendering index Ra as 93. The results imply the red‐emitting Sr3Lu(VO4)3:Eu3+ phosphors could be potentially utilized in the fields of solid‐state lighting.

Structural and Photoluminescence Investigations of Tb3+/Eu3+ Co-Doped Silicate Sol-Gel Glass-Ceramics Containing CaF2 Nanocrystals.

In this work, the series of Tb3+/Eu3+ co-doped xerogels and derivative glass-ceramics containing CaF2 nanocrystals were prepared and characterized. The in situ formation of fluoride crystals was verified by an X-ray diffraction technique (XRD) and transmission electron microscopy (TEM). The studies of the Tb3+/Eu3+ energy transfer (ET) process were performed based on excitation and emission spectra along with luminescence decay analysis. According to emission spectra recorded under near-ultraviolet (NUV) excitation (351 nm, 7F6 → 5L9 transition of Tb3+), the mutual coexistence of the 5D4 → 7FJ (J = 6–3) (Tb3+) and the 5D0 → 7FJ (J = 0–4) (Eu3+) luminescence bands was clearly observed. The co-doping also resulted in gradual shortening of a lifetime from the 5D4 state of Tb3+ ions, and the ET efficiencies were varied from ηET = 11.9% (Tb3+:Eu3+ = 1:0.5) to ηET = 22.9% (Tb3+:Eu3+ = 1:2) for xerogels, and from ηET = 25.7% (Tb3+:Eu3+ = 1:0.5) up to ηET = 67.4% (Tb3+:Eu3+ = 1:2) for glass-ceramics. Performed decay analysis from the 5D0 (Eu3+) and the 5D4 (Tb3+) state revealed a correlation with the change in Tb3+–Eu3+ and Eu3+–Eu3+ interionic distances resulting from both the variable Tb3+:Eu3+ molar ratio and their partial segregation in CaF2 nanophase.

Universal Conditional Distribution Function of [O ii] Luminosity of Galaxies, and Prediction for the [O ii] Luminosity Function at Redshift z &lt; 3

Abstract The star-forming emission line galaxies (ELGs) with a strong [O ii] doublet are one of the main spectroscopic targets for the ongoing and upcoming fourth-generation galaxy redshift surveys. In this work, we measure the [O ii] luminosity L [O II] and the absolute magnitude in the near-ultraviolet (NUV) band M NUV for a large sample of galaxies in the redshift range 0.6 ≤ z &lt; 1.45 from the Public Data Release 2 (PDR-2) of the VIMOS Public Extragalactic Redshift Survey (VIPERS). We aim to construct the intrinsic relationship between L [O II] and M NUV through Bayesian analysis. In particular, we develop two different methods to properly correct for the incompleteness effect and observational errors in the [O ii] emission line measurement. Our results indicate that the conditional distribution of L [O II] at a given M NUV can be well described by a universal probability distribution function (PDF), which is independent of M NUV and redshift. Convolving the L [O II] conditional PDF with the NUV luminosity function (LF) available in the literature, we make a prediction for [O ii] LFs at z &lt; 3. The predicted [O ii] LFs are in good agreement with the observational results from the literature. Finally, we utilize the predicted [O ii] LFs to estimate the number counts of [O ii] emitters for the Subaru Prime Focus Spectrograph survey. This universal conditional PDF of L [O II] provides a novel way to optimize the source targeting strategy for [O ii] emitters in future galaxy redshift surveys, and to model [O ii] emitters in theories of galaxy formation.

A novel quinoline derivative containing a phenanthroimidazole moiety: Synthesis, physical properties and light-emitting diodes application

The deep-blue emitting material 2-(8-(benzyloxy)quinolin-2-yl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (QL-PPI) which contains 8-(Benzyloxy)quinoline core and phenanthroimidazole moiety, has been designed and synthesized. The non-doped OLED using QL-PPI as the emitting layer shows emission at 455 nm, full width at half maximum of 100 nm, maximum brightness of 250 cd m−2, maximum current efficiency of 0.47 cd A−1, and Commission Internationale de L'Eclairage (CIE) coordinate of (0.20, 0.22). Furthermore, the QL-PPI with a slight mass concentration in the silica gel is coated on the near ultraviolet (NUV) chip (380 nm) to prepare the hybrid deep-blue LED device HB1 with a y coordinate = 0.0541. The hybrid WLED device HW1 based on QL-PPI mixed with green phosphor [(Ba, Sr)2SiO4: Eu2+] and red phosphor [(Sr, Ca)2AlSiN3: Eu2+] is prepared. The hybrid WLED exhibits luminance efficiency of 18.05 lm W−1 (at 19.90 mA), Correlated Color Temperature (CCT) of 4580 K, Color Rendering Index (CRI) of 80, and CIE chromaticity coordinate of (0.3571, 0.3562). These results reveal that the QL-PPI can apply both in OLED and the hybrid LED simultaneously. The QL-PPI which used in the hybrid WLED has the potential to reduce reliance on rare-earth metals and improve the CRI of the hybrid WLED.

Enhanced color rendering index of organic/inorganic hybrid white light-emitting diodes with trans-1-(9-anthryl)-2-phenylethene derivatives as organic blue-green emitting materials

Abstract The organic light-emitting materials have made certain development in organic/inorganic hybrid white light-emitting diodes (WLED) devices, which can reduce the reliance on rare earth metal materials to some extent. However, there is an urgent need to improve the color rendering index (CRI) of the hybrid WLED. Herein, the organic blue-green emitting materials mixed with green and red phosphors are used to construct the hybrid WLED. The device W19 is prepared by using the blue-green emitting material (E)-9-(4-(2-(anthracen-9-yl)vinyl)phenyl)-10-(naphthalen-1-yl)anthracene (APEAn1N) mixed with green (BaSi2N2O2: Eu2+) and red (Sr, Ca)2AlSiN3: Eu2+ phosphors coated on near ultraviolet (NUV) LED chips (380 nm). The device W19 exhibits luminance efficiency of 17.78 lm W−1 (at 19.90 mA), CCT of 4658 K, CRI of 86.7, and CIE chromaticity coordinate of (0.3633, 0.4125), respectively. The CRI of device W22 based on tri-primary color phosphors and blue-green phosphor is 79.4 which is inferior to W19. The WLED device based on organic blue-green emitting materials blended with green and red phosphors has evident advantages for reducing of the reliance on rare earth metals and improving the CRI of hybrid device, which will greatly inspire us to design and synthesize new blue-green materials and facilitate the development of hybrid WLEDs in future.

Controlled synthesis and photoluminescence properties of Bi2SiO5:Eu3+ core-shell nanospheres with an intense 5D0→7F4 transition

Core-shell Bi2SiO5 nanosystem with uniform morphology and narrow size distribution has been successfully synthesized via a facile template-assisted route. With the introduction of Eu3&#x002B;, detailed studies are performed to evaluate its promise as Eu3&#x002B;-based phosphor host. The yielded Bi2SiO5:Eu3&#x002B; nanospheres are proven to be pure tetragonal phase via X-ray diffraction and Rietveld refinement. Moreover, the phosphor particles consist of monodisperse spheres with an average diameter of approximately 285&#x2005;nm by high-resolution electron microscopy. When excited by near-ultraviolet (NUV) light, the abnormally high-intensity emission at 703&#x2005;nm arising from the 5D0&#x2192;7F4 transition of Eu3&#x002B; is observed. The temperature-dependent photoluminescence spectra show that the optimized Bi2SiO5:20&#x0025;Eu3&#x002B; have satisfactory thermal stability with 63.7&#x0025; of emission intensity at 423&#x2005;K relative to 303&#x2005;K. The deep-red light-emitting diode (LED) device fabricated by coating NUV chip with the Bi2SiO5:20&#x0025;Eu3&#x002B; phosphors is demonstrated. The newly-developed Bi2SiO5:Eu3&#x002B; nanophosphors display commendable photoluminescence properties, demonstrating their promise as deep-red phosphor candidates for use in phosphor-converted LEDs.

Improved performance of InGaN/GaN Near-UV light-emitting diodes with staircase hole injector

We report the enhanced performance of near-ultraviolet (NUV) InGaN/GaN multiple quantum-well (MQW) light-emitting diodes (LEDs) with a staircase hole injector (SHI). Simulation results indicate that the internal electrostatic field in the QW of the LED-SHI is decreased owing to the reduced sheet charge density at the interface between QW and quantum barrier (QB) caused by the smaller In content difference. Additionally, the SHI structure in the QBs suppresses the ballistic or quasi-ballistic hole transport, thus enhancing efficient hole injection into the QWs. The radiative output power of an LED-SHI is increased by 25.3% at 300 mA over that of conventional LEDs with GaN QBs. The droop of internal quantum efficiency (IQE) an LED-SHI at 300 A·cm−1 is 6.1%, while the LED with GaN QBs has an IQE droop of 17.7%. The reduced IQE droop and increased radiative output power in the LED-SHI is attributed to the reduced hole overflow, increased hole injection into the MQW and the decreased electrostatic field in the MQWs. The results show that the SHI structure in the LED is promising for improved performance in high-power GaN-based NUV LEDs.