Near-ultraviolet Research Articles

Simultaneous Chandra and HST observations of the quiescent neutron star low-mass X-ray binaries in 47 Tucanae

ABSTRACT We present simultaneous Chandra X-ray Observatory and Hubble Space Telescope observations of three certain (X5, X7, W37) and two likely (X4, W17) quiescent neutron star low-mass X-ray binaries (qLMXBs) in the globular cluster 47 Tuc. We study these systems in the X-ray, optical, and near-ultraviolet (NUV) using the simultaneous data and additional non-contemporaneous HST data. We have discovered a blue and variable NUV counterpart to W17. We have not securely identified the eclipsing qLMXB W37 in the optical or NUV. Deeper high-resolution imaging is needed to further investigate the faint NUV excess near the centre of the W37 error circle. We suggest that a previously identified optical astrometric match to X7 is likely the true counterpart. The H α emission and the location of the counterpart in the colour–magnitude diagram, indicate that the secondary is probably a non-degenerate, H-rich star. This is consistent with previous results from fitting X7’s X-ray spectrum. In X4, the simultaneous X-ray and optical behaviour supports the earlier suggestion that the X-ray variability is driven by changes in accretion rate. The X-ray eclipses in X5 coincide with minima in the optical/NUV light curves. Comparison of the 47 Tuc qLMXBs with the cataclysmic variables (CVs) in the cluster confirms that overall the qLMXBs have larger X-ray to optical flux ratios. Based on their optical/NUV colours, we conclude that the accretion discs in the qLMXBs are less prominent than in CVs. This makes the ratio of X-ray flux to excess blue-optical flux a powerful discriminator between CVs and qLMXBs.

Probing the Stellar Populations and Star Formation History of Early-type Galaxies at 0 < z < 1.1 in the Rest-frame Ultraviolet

We measure the evolution of the rest-frame near-ultraviolet (NUV)−V colors for early-type galaxies in clusters at 0 < z < 1.1 using data from the Hyper Suprime-Cam Subaru Strategic Program, CFHT Large Area U-band Deep Survey, and local Sloan Digital Sky Survey clusters observed with Galaxy Evolution Explorer. Our results show that there is an excess in the ultraviolet spectrum in most quiescent galaxies (compared to the expectations from models fitting their optical/infrared colors and spectra) below z ∼ 0.6, beyond which the excess UV emission fades rapidly. This evolution of the UV color is only consistent with the presence of a highly evolved, hot horizontal branch subpopulation in these galaxies (among the majority of cool and optically bright stars), comprising on average 10% of the total stellar mass and forming at z > 3. The blue UV colors of early-type galaxies at low–intermediate redshifts are likely driven by this subpopulation being enriched in helium up to ∼44%. At z > 0.8 (when the extra UV component has not yet appeared) the data allow us to constrain the star formation histories of galaxies by fitting models to the evolution of their UV colors: we find that the epoch at which the stellar populations formed lies in the range 3 < z form < 10 (corresponding to 0.5–2.2 Gyr after the Big Bang) with a star formation e-folding timescale of τ = 0.35–0.7 Gyr, suggesting that these galaxies formed the majority of stars at very high redshift, with a brief yet intense burst of star formation activity. The star formation history and chemical evolution of early-type galaxies resemble those of globular clusters, albeit on much larger scales.

Improved Design of Slope-Shaped Hole-Blocking Layer and Electron-Blocking Layer in AlGaN-Based Near-Ultraviolet Laser Diodes.

The injection and leakage of charge carriers have a significant impact on the optoelectronic performance of GaN-based lasers. In order to improve the limitation of the laser on charge carriers, a slope-shape hole-barrier layer (HBL) and electron-barrier layer (EBL) structure are proposed for near-UV (NUV) GaN-based lasers. We used Crosslight LASTIP for the simulation and theoretical analysis of the energy bands of HBL and EBL. Our simulations suggest that the energy bands of slope-shape HBL and EBL structures are modulated, which could effectively suppress carrier leakage, improve carrier injection efficiency, increase stimulated radiation recombination rate in quantum wells, reduce the threshold current, improve optical field distribution, and, ultimately, improve laser output power. Therefore, using slope-shape HBL and EBL structures can achieve the superior electrical and optical performance of lasers.

CO emission survey of asymptotic giant branch stars with ultraviolet excesses

Context. The transition from the spherically symmetric envelopes around asymptotic giant branch (AGB) stars to the asymmetric morphologies observed in planetary nebulae is still not well understood, and the shaping mechanisms are a subject of debate. Even though binarity is widely accepted as a promising option, it is limited by the complication of identifying binary AGB stars observationally. Recently, the presence of ultraviolet excesses in AGB stars has been suggested as a potential indicator of binarity. Aims. Our main goals are to characterise the properties of the circumstellar envelopes (CSEs) around candidate AGB binary stars, specifically those selected based on their UV excess emission, and to compare these properties with those derived from previous CO-based studies of AGB stars. Methods. We observed the 12CO (J=1–0) and 12CO (J=2–1) millimetre-wavelength emission in a sample of 29 AGB binary candidates with the IRAM-30 m antenna. We measured the systemic velocities and the terminal expansion velocities from their line profiles. Population diagrams were used to interpret the results, enabling the estimation of excitation temperatures (Tex), mass-loss rates (Ṁ), and the characteristic sizes of the envelope layers where the CO millimetre emission originates (Rs). We explored different trends between the envelope parameters deduced, multiwavelength flux measurements, and other properties of our sample, and compared them with those previously derived from larger samples of AGB stars found in the literature. Results. We detected 12CO emission in 15 sources, of which 5 are first detections. We found relatively low expansion velocities (3 km s−1 ≲ Vexp ≲ 20 km s−1) in our sample. We derived the average excitation temperature and column density of the CO-emitting layers, which we used to estimate self-consistently the average mass-loss rate (10−8 M⊙ yr−1 ≲ Ṁ ≲ 10−5 M⊙ yr−1) and the CO pho-todissociation radius (5 × 1015 cm ≲ RCO ≲ 2 × 1017 cm) of our targets. We find a correlation between CO intensity and IRAS 60 µm fluxes, revealing a CO-to-IRAS 60 µm ratio lower than for AGB stars and closer to that found for pre-planetary nebulae (pPNe). An anti-correlation is observed between 12CO (and IRAS 60 µm) and the near-ultraviolet (NUV), but no such correlation is observed with the far-ultraviolet (FUV). It is also worth noting that there is no correlation between bolometric luminosity and NUV or FUV. Conclusions. For the first time we have studied the mass-loss properties of UV-excess AGB binary candidates and estimated their main CSE parameters. Our sample of uvAGB stars shows similarities with the broader category of AGB stars, except for a distinct CO-to-IRAS 60 µm trend suggesting enhanced CO photodissociation. Our findings, based on single-dish low-J CO line emission observations, support the dust-driven wind scenario and indicate that alternative mass-loss mechanisms are not necessary (in principle) to explain the ~200–2000 yr old mass-loss ejecta in uvAGBs. The different relationships between 12CO and IRAS 60 µm, with NUV and FUV are consistent with an intrinsic origin of NUV emission, but potential dominance of an extrinsic process (e.g. presence of a binary companion) in FUV emission.

Energy-transfer and charge-compensation jointly improved the luminescence of NaMgPO4:Eu2+,Tb3+ phosphor

Energy transfer from Eu2+ to Tb3+ is an efficient strategy to boost the luminescence of Tb3+ in many hosts. In this study, series of Eu2+/Tb3+ co-activated NaMgPO4 phosphors are synthesized. Under near ultraviolet (NUV) excitation, Eu2+ and Tb3+ co-doped NaMgPO4 phosphors show tunable emitting color from blue to green via the energy transfer from Eu2+ to Tb3+. Interestingly, the enhanced blue emission from Eu2+ is observed with codoping Tb3+ ions and the quantum efficiency of NaMgPO4:Eu2+ increases to three times. Photo-luminescence spectra and photo-phosphorescence spectra indicates the coexistence of Eu2+ and Eu3+. Substituting Tb3+ at the Na+ site generates positive charge defects, promotes the transformation of Eu3+, increases the effective concentration of Eu2+ ions, and enhances the emission of Eu2+ finally. The strategy clarified in this study might work for other Eu2+/Tb3+ codoped phosphors.

Enhanced activation of sulfite by the iron-citrate complexes under NUV irradiation for metronidazole degradation: Kinetic, degradation mechanism and efficiency in real water

In the present study, a novel approach for the elimination of emerging pollutants through an advanced oxidation process has been developed by combining near ultraviolet (NUV) irradiation with an iron-citrate complex (Fe(III)-Cit) to overcome the defects of the traditional Fe(III)/sulfite system and enhance the activation of sulfite in a neutral aqueous solution. The performance of this system was studied using metronidazole (MTZ) as the target pollutant, and the impact of operational conditions such as initial pH, Fe(III)-Cit complex concentration, sulfite dose, metronidazole concentration and dissolved oxygen were studied. The rate constant of MTZ degradation at natural pH (7.0 ± 0.2) by the Fe(III)-Cit/sulfite/NUV system is over 12.72-times and 13.25-times higher than the sulfite/NUV and Fe(III)-Cit/NUV individual binary systems. The effectiveness of the system was further examined in various real water matrices. The latter proved to be effective in the following order: groundwater > ultra-pure water > > seawater, revealing that it was very effective in the former. Chemical probe experiments indicated that sulfate radicals and hydroxyl radicals were the principal reactive oxygen species involved in the photodegradation of MTZ. Additionally, dissolved oxygen played a crucial role in the reaction. MTZ degradation products were determined by HPLC/MS, leading to the identification of nine different by-products and the proposal of possible degradation pathways. Although further studies are required to better understand this system, this work paves the way for the application of activated sulfite-based processes for environmental remediation without pH adjustment, offering an alternative to the use of conventional oxidants.

A dragon’s flame of many colours: multiwavelength observations of flares from the active M binary CR Draconis

ABSTRACT We present the results of a multiwavelength Professional–Amateur campaign to study the behaviour of flares from the active M1.5V star binary CR Draconis. CR Dra was observed with Transiting Exoplanet Survey Satellite (TESS) 20-s photometry, Swift near-ultraviolet (NUV) grism spectroscopy and with ground-based optical photometry and spectroscopy from a global collaboration of amateur astronomers. We detected 14 flares with TESS and Swift simultaneously, one of which also had simultaneous ground-based photometry and spectroscopy. We used the simultaneous two-colour optical and NUV observations to characterize the temperature evolution of the flare and test the accuracy of using optical data to predict NUV emission. We measured a peak temperature of $7100^{+150}_{-130}$ K for this flare, cooler than the typically assumed 9000 K blackbody model used by flare studies. We also found that the 9000 K blackbody overestimated the NUV flux for other flares in our sample, which we attributed to our Swift observations occurring during flare decays, highlighting the phase-dependence for the accuracy of flare models.

Evidence of extended [CII] and dust emission in local dwarf galaxies

Aims. The evolution of dwarf galaxies is dramatically affected by gaseous and dusty outflows, which can easily deprive their interstellar medium of the material needed for the formation of new stars, simultaneously enriching their surrounding circumgalactic medium (CGM). In this Letter, we present the first evidence of extended [CII] 158 μm line and dust continuum emission in local dwarf galaxies hosting star-formation-driven outflows. Methods. By stacking the [CII], far-infrared, and near-UV (NUV) emission obtained from Herschel and GALEX data, we derived the average radial profiles, and compared the spatial extension of gas, dust, and stellar activity in dwarf galaxies. Results. We find that [CII] and dust emissions are comparable to each other, and more extended than the NUV continuum. The [CII] size is in agreement with that measured for z &gt; 4 star-forming galaxies, suggesting that similar mechanisms could be at the origin of the observed atomic carbon reservoir around local and high-z sources. The cold dust follows the [CII] emission, going beyond the stellar continuum as opposed to what is typically observed in the early Universe where measurements can be affected by the poor sensitivity and faintness of dust emission in the CGM of high-z galaxies. Conclusions. We attribute the extended [CII] and dust continuum emission to the presence of galactic outflows. As local dwarf galaxies are considered analogs of primordial sources, we expect that comparable feedback processes can be at the origin of the observed [CII] halos at z &gt; 4, dominating over other possible formation mechanisms.

A narrow-band blue emitting phosphor by co-doping Bi3+ and alkali metal ions (Li+, Na+ and K+) with dual luminescence center

The technology of solid-state lighting has developed for decades in various industries. Phosphor, as an element part, determines the application domain of lighting products. For instance, blue and red-emitting phosphors are required in the process of plant supplementing light, arrow-band emitting phosphors are applied to backlight displays, etc. In this work, a Bi3+-activated blue phosphor is obtained in a symmetrical and compact crystal structure of Gd3SbO7 (GSO). Then, the co-doping strategy of alkali metal ions (Li+, Na+, and K+) is used to optimize the performance. The result shows that the photoluminescence intensity is increased by 2.1 times and 1.3 times respectively by introducing Li+ and K+ ions. Not only that, it also achieves narrow-band emitting with the full width of half-maximum (FWHM) reaching 42 nm through Na+ doping, and its excitation peak position also shifts from 322 to 375 nm, which can be well excited by near-ultraviolet (NUV) light emitting diode (LED) chips (365 nm). Meanwhile, the electroluminescence spectrum of GSO:0.6 mol%Bi3+,3 wt%Na+ matches up to 93.39% of the blue part of the absorption spectrum of chlorophyll a. In summary, the Bi3+-activated blue phosphor reported in this work can synchronously meet the requirements of plant light replenishment and field emission displays.

On the Existence, Rareness, and Uniqueness of Quenched H i-rich Galaxies in the Local Universe

Using data from ALFALFA, xGASS, H i-MaNGA, and the Sloan Digital Sky Survey (SDSS), we identify a sample of 47 “red but H i-rich” (RR) galaxies with near-UV (NUV) − r > 5 and unusually high H i-to-stellar mass ratios. We compare the optical properties and local environments between the RR galaxies and a control sample of “red and H i-normal” (RN) galaxies that are matched in stellar mass and color. The two samples are similar in the optical properties typical of massive red (quenched) galaxies in the local Universe. The RR sample tends to be associated with slightly lower-density environments and has lower clustering amplitudes and smaller neighbor counts at scales from several hundred kiloparsecs to a few megaparsecs. The results are consistent with the RR galaxies being preferentially located at the center of low-mass halos, with a median halo mass ∼1012 h −1 M ⊙ compared to ∼1012.5 h −1 M ⊙ for the RN sample. This result is confirmed by the SDSS group catalog, which reveals a central fraction of 89% for the RR sample, compared to ∼60% for the RN sample. If assumed to follow the H i size–mass relation of normal galaxies, the RR galaxies have an average H i-to-optical radius ratio of R HI/R 90 ∼ 4, four times the average ratio for the RN sample. We compare our RR sample with similar samples in previous studies, and quantify the population of RR galaxies using the SDSS complete sample. We conclude that the RR galaxies form a unique but rare population, accounting for only a small fraction of the massive quiescent galaxy population. We discuss the formation scenarios of the RR galaxies.

Stellar Loci. VII. Photometric Metallicities of 5 Million FGK Stars Based on GALEX GR6+7 AIS and Gaia EDR3

We combine photometric data from GALEX GR6+7 All-Sky Imaging Survey and Gaia Early Data Release 3 with stellar parameters from the SAGA and PASTEL catalogs to construct high-quality training samples for dwarfs (0.4 < BP − RP < 1.6) and giants (0.6 < BP − RP < 1.6). We apply careful reddening corrections using empirical temperature- and extinction-dependent extinction coefficients. Using the two samples, we establish a relationship between stellar loci (near-ultraviolet (NUV)−BP versus BP − RP colors), metallicity, and M G . For a given BP − RP color, a 1 dex change in [Fe/H] corresponds to an approximately 1 magnitude change in NUV − BP color for solar-type stars. These relationships are employed to estimate metallicities based on NUV − BP, BP − RP, and M G . Thanks to the strong metallicity dependence in the GALEX NUV band, our models enable a typical photometric-metallicity precision of approximately σ [Fe/H] = 0.11 dex for dwarfs and σ [Fe/H] = 0.17 dex for giants, with an effective metallicity range extending down to [Fe/H] = −3.0 for dwarfs and [Fe/H] = −4.0 for giants. We also find that the NUV-band-based photometric-metallicity estimate is not as strongly affected by carbon enhancement as previous photometric techniques. With the GALEX and Gaia data, we have estimated metallicities for about 5 million stars across almost the entire sky, including approximately 4.5 million dwarfs and 0.5 million giants. This work demonstrates the potential of the NUV band for estimating photometric metallicities, and sets the groundwork for utilizing the NUV data from space telescopes such as the upcoming Chinese Space Station Telescope.

Enhanced near-UV responsivity of AlGaN/GaN HEMT based photodetectors by nanohole etching of barrier surface

We demonstrate the fabrication of unpatterned and nanohole patterned AlGaN/GaN High electron mobility transistor-based metal-semiconductor-metal UV photodetectors. Device with shallow, non-dense periodic arrays of 200 nm diameter and 20 nm deep nanoholes on the AlGaN barrier surface shows ∼ 103 photo-to-dark current ratio and responsivity of 1.3×105 A/W for 325 nm wavelength at 5 V bias. Nanohole etching on AlGaN barrier surface is shown to enhance the spectral response of the devices in the near UV (NUV) range, with clear UV/Visible cut-off. The enhancement is attributed to light trapping in nanoholes which prolonged light path and enhanced absorption in the active region. External quantum efficiency of the devices exceeded 100 %, due to internal gain mechanism of the device. Two spectral responsivity peaks occurred at wavelengths correspond to AlGaN and GaN bandgaps. The device performance shows the importance of embedding GaN native nanostructures to enhance UV detection.

A record-high EQE of 7.65%@3300 cd m-2 achieved in non-doped near-ultraviolet OLEDs based on novel D'-D-A type bipolar fluorophores upon molecular configuration engineering.

Developing a high-performance near-ultraviolet (NUV) material and its simple non-doped device with a small efficiency roll-off and good color purity is a promising but challenging task. Here, we proposed a novel donor'-donor-acceptor (D'-D-A) type molecular strategy to largely solve the intrinsic contradictions among wide-bandgap NUV emission, fluorescence efficiency, carrier injection and transport. An efficient NUV fluorophore, 3,6-mPPICNC3, exhibiting a hybridized local and charge-transfer state, is achieved through precise molecular configuration engineering, realizing similar hole and electron mobilities at both low and high electric fields. Moreover, the planarized intramolecular charge transfer excited state and steric hindrance effect endow 3,6-mPPICNC3 with a considerable luminous efficiency and good color purity in the aggregation state. Consequently, the non-doped device emitting stable NUV light with Commission Internationale de l'Eclairage (CIE) coordinates of (0.160, 0.032) and a narrow full width at half maximum of 44 nm exhibits a state-of-the-art external quantum efficiency (EQE) of 7.67% and negligible efficiency roll-off over a luminance range from 0 to 3300 cd m-2. This is a record-high efficiency among all the reported non-doped NUV devices. Amazingly, an EQE of 7.85% and CIE coordinates of (0.161, 0.025) are achieved in the doped device. This demonstrates that the D'-D-A-type molecular structure has great potential for developing high-performance organic light-emitting materials and their optoelectronic applications.

Constraining the top-light initial mass function in the extended ultraviolet disk of M 83

Context. The universality or non-universality of the initial mass function (IMF) has significant implications for determining star formation rates and star formation histories from photometric properties of stellar populations. Aims. We reexamine whether the IMF is deficient in high-mass stars (top-light) in the low-density environment of the outer disk of M 83 and constrain the shape of the IMF therein. Methods. Using archival Galaxy Evolution Explorer (GALEX) far ultraviolet (FUV) and near ultraviolet (NUV) data and new deep OmegaCAM narrowband Hα imaging, we constructed a catalog of FUV-selected objects in the outer disk of M 83. We counted Hα-bright clusters and clusters that are blue in FUV−NUV in the catalog, measured the maximum flux ratio FHα/fλFUV among the clusters, and measured the total flux ratio ΣFHα/ΣfλFUV over the catalog. We then compared these measurements to predictions from stellar population synthesis models made with a standard Salpeter IMF, truncated IMFs, and steep IMFs. We also investigated the effect of varying the assumed internal extinction on our results. Results. We are not able to reproduce our observations with models using the standard Salpeter IMF or the truncated IMFs. It is only when assuming an average internal extinction of 0.10 &lt; AV &lt; 0.15 in the outer disk stellar clusters that models with steep IMFs (α &gt; 3.1) simultaneously reproduce the observed cluster counts, the maximum observed FHα/fλFUV, and the observed ΣFHα/ΣfλFUV. Conclusions. Our results support a non-universal IMF that is deficient in high-mass stars in low-density environments.

Electroluminescence efficiency and stability of near ultraviolet organic light-emitting diodes based on BCPO luminous materials

To date, in the traditional method of obtaining near-ultraviolet (NUV) light, mercury atoms, which can create a highly toxic heavy metal contaminant, have been used. Therefore, it is an important issue to obtain NUV light by using new environmentally friendly devices. In the last decade, the fabrication of near ultraviolet organic light-emitting diodes (NUV-OLEDs) has become a research hotspot in the field of organic electronics. However, when the electroluminescence wavelength is extended to shorter than 400 nm, higher requirements are put forward for the materials used for each functional layer in these devices. In this work, a wide bandgap small molecule material of BCPO is used as the luminescent layer. The electron-transporting and hole-transporting materials are determined based on the overlaps between absorption spectra of these materials and emission spectrum of BCPO. And NUV-OLEDs with electroluminescent peak wavelength at 384 nm are prepared. By using the optimal device structure, the maximum external quantum efficiency of the device reaches 2.98%, and the maximum radiance of the device reaches 38.2 mW/cm&lt;sup&gt;2&lt;/sup&gt;. In the electroluminescence spectrum, NUV light with wavelengths below 400 nm accounts for 57% of the light emission. In addition, the device demonstrates good stability when biased at two different constant voltage modes. The multiple key factors which affect the stability of the device are analyzed in detail. Firstly, it is found that the high glass transition temperature (&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;g&lt;/sub&gt;) of hole-transporting material is very important for the long-time stability of this device. The poor device stability is closely related to the low &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;g&lt;/sub&gt; temperature of hole-transporting material. Secondly, due to the widespread use of PEDOT:PSS as hole injection material in OLEDs, the electron leakage from the hole-transpor layer into the PEDOT:PSS layer may cause significant damage to the conducting polymer. When bombarded with low energy electrons, bond breakage occurs on the surface of PEDOT:PSS, followed by the release of oxygen and sulfur, resulting in changes in conductivity and oxidation reactions with molecules of hole transport material. Thirdly, the photoelectrical stability of organic molecules is the most fundamental reason that restricts the device lifetime. The aging process of material or device is directly relevant to the bond dissociation energy (BDE) of organic molecule. Generally, the BDE value of organic molecule is not high enough. As a result, molecules are prone to chemical bond breakage during electrochemical or photochemical aging. In summary, highly stable NUV-OLEDs should be fabricated by using hole-transporting materials with high &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;g&lt;/sub&gt; temperature, sufficient electron-blocking capacity, and large BDE value.

Highly efficient pure organic near-ultraviolet (NUV) electro-fluorescent materials with high electron mobility and improved hole mobility.

The lack of blue-emissive materials with high efficiency and excellent color purity commonly represents a pivotal obstacle in the development of organic light-emitting diodes (OLEDs). In this work, two blue to near-ultraviolet (NUV) donor-π-acceptor (D-π-A) emitters based on a fluorene π-bridge, 9-PCZCFTZ and 3-PCZCFTZ, are thus designed and synthesized, and non-doped devices derived from these two materials exhibit electroluminescence (EL) emission peaks at 404 nm and 417 nm, respectively. Interestingly, due to the specific stacking, a phenomenon appears in both materials in which the mobility of the electron is much higher than that of the hole, prompting us to use host doping to increase the hole mobilities, which ultimately leads to excellent OLED performances. As a result, the maximum external quantum efficiency (EQEmax) values of 9-PCZCFTZ and 3-PCZCFTZ in the doped devices reach as high as 14.5% and 10.8% respectively. Notably, both OLEDs show high blue purity very close to the BT.2020 standard.

Novel Eu3+-activated Ca3Ga2Ge4O14 red-emitting phosphors with high quantum efficiency for plant growth lighting and white LEDs.

In recent years, rare-earth-based phosphors for near-ultraviolet (NUV)-triggered white light emitting diodes (w-LEDs) have become a research hotspot. However, it is still not possible to obtain phosphors with high quantum yield, excellent color purity and multiple applications. Hence, a series of novel Eu3+-activated Ca3Ga2Ge4O14 (CGG) red-emitting phosphors with high quantum efficiency, excellent color purity and good thermal stability were prepared by a high-temperature solid-phase method. All the CGG:Eu3+ phosphors emitted dazzling red emission with excitation at 394 nm. The optimal Eu3+ doping concentration of compounds was 12% with an excellent color purity of 97.89%, and the concentration quenching mechanism was investigated as dipole-dipole interactions. Meanwhile, the synthetic samples exhibited good thermal stability with the activation energy of 0.26 eV. Remarkably, the internal quantum yield of the prepared phosphors reaches 94.26%. Furthermore, the emission spectra of the prepared red-LEDs overlap considerably with the absorption spectra of PR and PFR required for plant growth. The w-LED device emits warm white light with a high color rendering index of 91.64 and an appropriate correlated color temperature of 4808 K. These excellent luminescence properties indicate that the prepared CGG:Eu3+ phosphors exhibit extensive potential for applications in plant growth lighting and white LEDs.

Luminescent properties of ZSM-5 zeolite phosphor and its application to aquatic plant lighting and white LEDs

In order to explore ideal materials with suitable excitation wavelengths, high thermal stability and good emission characteristics for phosphor-converted white light emitting diodes (pc-WLEDs), in this work, a blueish-white phosphor (λex = 390 nm) was realized by a new strategy of carbocations formation in ZSM-5 zeolite, which maintains the luminescence intensity at 473 K is 103% of that at room temperature. Following immersion in ethanol, water, 40 wt% sodium hydroxide solution (NaOH), and concentrated hydrochloric acid (HCl) for 120 h, the luminescence intensity was maintained at 92%, 87%, 80%, and 82% of the normal state, respectively. By packaging the sample on a near-ultraviolet (NUV) chip (390 nm), a blueish-white pc-LED was fabricated, which has a promising commercial prospect in the field of aquatic plant lighting. Meanwhile, a pc-WLED device was fabricated by combining a 390 nm NUV chip and ZSM-5 zeolite and red phosphor K2MgGeO4:Eu3+. It has an excellent property with the correlated color temperature (CCT) = 4600 K and color rendering index (CRI) = 91.5, indicating that ZSM-5 zeolite has good application prospects in the pc-WLEDs field.

Spectral tunability of K2Lu(WO4)(PO4): Dy3+, Eu3+ phosphors and remote luminescent layers for high-quality white light

Dy3+ and Eu3+ co-doped phosphors have been emerged as potential candidate to generate high-quality white light under the ultraviolet (UV) or near ultraviolet (NUV) excitation for health and comfort lighting. Herein, K2Lu(WO4)(PO4) crystal has been newly developed to accommodate rare earth ions, such as Dy3+ and Eu3+ ions, to achieve spectral tunability of high-quality white light. Under NUV excitation, Dy3+ singly-doped K2Lu(WO4)(PO4) phosphors exhibit the desired blue emission at 486 nm and yellow emission at 575 nm, attributed to the electric dipole transition 4F9/2 → 6H15/2 and the magnetic dipole transition 4F9/2 → 6H13/2 transitions of Dy3+ ions, respectively. Interestingly, the emission color can be facilely adjusted from cold white light to pink light under 365 nm NUV excitation due to the co-doping of Eu3+ ions in K2Lu(WO4)(PO4): 0.05Dy3+ sample. Further, the remote luminescent layers containing K2Lu(WO4)(PO4): 0.05Dy3+, 0.20Eu3+ phosphor can be printed on glass substrate by screen printing technique to generate high-quality white light with the correlated color temperature (CCT) of 5433 K and color rendering index (CRI) of 87. Moreover, the remote luminescent layers exhibit better heat dissipation performance compared to conventional encapsulated LEDs and can be used as a multicolor emitting candidate for high-power white LEDs.

Insight into the optical evaluation of sunlike LED devices with full-visible spectrum emission based on ultra-low melting tin fluorophosphate glass for human centric lighting

Full spectrum sunlike light-emitting diode (LED) devices in the wavelength range of 380–670 nm have received much attention for their applications in human centric lighting. Herein, the inorganic color converter of the sunlike phosphor-in-glass (PiG) has been developed by embedding the green-emitting (Lu3-xYxAl5O12: Ce3+) and red-emitting (Sr0.6Ca0.4AlSiN3: Eu2+) phosphor powders in ultra-low melting tin fluorophosphate glass. Notably, the sunlike PiG exhibits the full spectrum in the wavelength range of 380–670 nm under the excitation of a near-ultraviolet (NUV) chip. Tunable color temperature (2785 K–5806 K) and high color rendering index (Ra = 95) were obtained by varying the mix ratio of the red-emitting component in the glass matrix. Further, the full visible spectrum emission was regulated by adjusting the Lu/Y ratio of the green phosphor Lu3-xYxAl5O12: Ce3+ and the color quality was further optimized (Ra = 97). The color quality of white light-emitting diode (WLED) was systematically investigated using Illuminating Engineering Society (IES) of North America evaluation systems and the LED devices exhibit fidelity index (Rf) and gamut index (Rg) close to sunlight (Rf = 95, Rg = 101). Compared with the traditional phosphor-in-silicone (PiS), the sunlike PiG based WLED exhibits a low working temperature of ∼37 °C for high power LED. Therefore, the WLED devices based on sunlike-PiG can be regarded as promising candidates for ultra-high color rendering index light sources because of the adjustable color temperature, high color quality, low-efficiency loss, excellent thermal properties and water stability.