Broad Red Band Research Articles

Manipulating Lone-Pair-Driven Luminescence in 0D Tin Halides by Pressure-Tuned Stereochemical Activity from Static to Dynamic.

The excellent luminescence properties and structural dynamics driven by the stereoactivity of the lone pair in a variety of low-dimensional ns2 metal halides have attracted growing investigations for optoelectronic applications. However, the structural and photophysical aspects of the excited state associated with the lone pair expression are currently open questions. Herein, zero-dimensional Sn-based halides with static stereoactive 5 s2 lone pairs are selected as a model system to understand the correlations between the distinctive lone pair expression and the excited-state structural relaxation and charge carrier dynamics by continuous lattice manipulation. Lattice compression drives 5 s2 lone pair active switching and self-trapped exciton (STE) redistribution by suppressing excited-state structural deformation of the isolated SnBr4 2- units. Our results demonstrate that the static expression of the 5 s2 lone pair results in a red broadband triplet STE emission with a large Stokes shift, while its dynamic expression creates a sky-blue narrowband emission dominated by the radiative recombination of singlet STEs. Our findings and the photophysical mechanism proposed highlight the stereochemical effects of lone pair expression in controlling light emission properties and offer constructive guidelines for tuning the optoelectronic properties in diverse ns2 metal halides.

Manipulating Lone‐Pair‐Driven Luminescence in 0D Tin Halides by Pressure‐Tuned Stereochemical Activity from Static to Dynamic

AbstractThe excellent luminescence properties and structural dynamics driven by the stereoactivity of the lone pair in a variety of low‐dimensional ns2 metal halides have attracted growing investigations for optoelectronic applications. However, the structural and photophysical aspects of the excited state associated with the lone pair expression are currently open questions. Herein, zero‐dimensional Sn‐based halides with static stereoactive 5 s2 lone pairs are selected as a model system to understand the correlations between the distinctive lone pair expression and the excited‐state structural relaxation and charge carrier dynamics by continuous lattice manipulation. Lattice compression drives 5 s2 lone pair active switching and self‐trapped exciton (STE) redistribution by suppressing excited‐state structural deformation of the isolated SnBr42− units. Our results demonstrate that the static expression of the 5 s2 lone pair results in a red broadband triplet STE emission with a large Stokes shift, while its dynamic expression creates a sky‐blue narrowband emission dominated by the radiative recombination of singlet STEs. Our findings and the photophysical mechanism proposed highlight the stereochemical effects of lone pair expression in controlling light emission properties and offer constructive guidelines for tuning the optoelectronic properties in diverse ns2 metal halides.

Probabilistic classification of infrared-selected targets for SPHEREx mission: in search of young stellar objects

ABSTRACT We apply machine learning algorithms to classify infrared (IR)-selected targets for NASA’s upcoming Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) mission. In particular, we are interested in classifying young stellar objects (YSOs), which are essential for understanding the star formation process. Our approach differs from previous works, which have relied heavily on broad-band colour criteria to classify IR-bright objects, and are typically implemented in colour–colour and colour–magnitude diagrams. However, these methods do not state the confidence associated with the classification and the results from these methods are quite ambiguous due to the overlap of different source types in these diagrams. Here, we utilize photometric colours and magnitudes from seven near- and mid-IR bands simultaneously and employ machine and deep learning algorithms to carry out probabilistic classification of YSOs, asymptotic giant branch (AGB) stars, active galactic nuclei (AGNs), and main-sequence (MS) stars. Our approach also subclassifies YSOs into Class I, II, III, and flat spectrum YSOs, and AGB stars into carbon-rich and oxygen-rich AGB stars. We apply our methods to IR-selected targets compiled in preparation for SPHEREx which are likely to include YSOs and other classes of objects. Our classification indicates that out of 8308 384 sources, 1966 340 have class prediction with probability exceeding 90 per cent, amongst which $\sim 1.7~{{\ \rm per\ cent}}$ are YSOs, $\sim 58.2~{{\ \rm per\ cent}}$ are AGB stars, $\sim 40~{{\ \rm per\ cent}}$ are (reddened) MS stars, and $\sim 0.1~{{\ \rm per\ cent}}$ are AGNs whose red broad-band colours mimic YSOs. We validate our classification using the spatial distributions of predicted YSOs towards the Cygnus-X star-forming complex, as well as AGB stars across the Galactic plane.

High-resolution flexible X-ray luminescence imaging enabled by eco-friendly CuI scintillators.

Solution-processed scintillators hold great promise in fabrication of low-cost X-ray detectors. However, state of the art of these scintillators is still challenging in their environmental toxicity and instability. In this study, we develop a class of tetradecagonal CuI microcrystals as highly stable, eco-friendly, and low-cost scintillators that exhibit intense radioluminescence under X-ray irradiation. The red broadband emission is attributed to the recombination of self-trapped excitons in CuI microcrystals. We demonstrate the incorporation of such CuI microscintillator into a flexible polymer to fabricate an X-ray detector for high-resolution imaging with a spatial resolution up to 20 line pairs per millimeter (lp mm-1), which enables sharp image effects by attaching the flexible imaging detectors onto curved object surfaces.

Far-red-emitting SrGdAlO4:Cr3+,Bi3+ phosphors for plant growth regulation

In modern agriculture, light plays an important role in plant growth. Far red light controls the whole growth process of plants from germination to vegetative growth to flowering. Here, we report the preparation and photoluminescence (PL) performance of Cr,Bi co-doped SrGdAlO4 phosphors by solution combustion method. The SrGdAlO4:Cr3+,Bi3+ phosphors exhibit far red broadband PL of 660–780 nm excited at 458 nm, and the maximum emission peak position is at 713 nm. It was found Cr3+ and Bi3+ replaced the positions of Al3+ and Gd3+ in the host material, respectively. The PL performance of SrGdAlO4:Cr3+,Bi3+ phosphors mainly depends on the 2E2 → 4A2 transition of Cr3+, and the addition of Bi3+ can effectively enhance the PL intensity of the phosphors. Notably, the SrGdAlO4:Cr3+,Bi3+ phosphors also exhibit obvious far red PL when coated onto glass substrate or mixed with plastics without affecting their visible light transmission. We believe our work will excite interests in further exploring the practical application of SrGdAlO4:Cr3+,Bi3+ phosphors as plant growth regulator in greenhouse.

A precisely space-separated strategy of donor-acceptor for intense red emitting composite borosilicate glass co-doped with CsPbCl3 quantum dots and Mn2+ ions

Optical ions doped transparent glasses have attracted more and more attention because of their potential application in photonic applications. Unfortunately, optically active dopants occupy at non-crystalline coordination environment, which leads to their poor luminescence efficiency. Therefore, how to enhance luminescence efficiency of optically active dopants in glasses remains a great challenge. Here, we proposed a precisely space-separated strategy of donor-acceptor and successfully developed an intense red emitting composite borosilicate glass co-doped with CsPbCl3 quantum dots and Mn2+ ions. By rationally controlling post heat-treatment, CsPbCl3 QDs acting as donor were uniformly precipitated in glass and Mn2+ ions acting as acceptor are close to CsPbCl3 QDs but not inside CsPbCl3 QDs. Benefitted from high absorption efficiency of CsPbCl3 QDs and efficient energy transfer from CsPbCl3 QDs to Mn2+ ions in glasses, Mn2+ ions give an intense red broadband emission at 650 nm, 11 times as intense as the one without CsPbCl3 QDs. The optimal external quantum yield of the as-synthesized composite borosilicate glass is estimated to be 28.5%, 9.5 times as large as 3% for the one without CsPbCl3 QDs. The precise space-separation and energy transfer rate dependent non-radiative energy coupling mechanism was reasonably proposed to explain how CsPbCl3 QDs highly absorb energy, efficiently transfer it and finally feeding Mn2+ ion. These results demonstrate that the strategy of using microcrystalline with high absorption efficiency as donor, for instance, CsPbX3 QDs, to pump optical activator ions as acceptor, for instance, Mn2+ ion in glass may be very promising for developing high luminescent performance ions-doped transparent glasses.

Novel Tunable Green-Red Luminescence in Mn2+ Doped Ca9Tb(PO4)7 Phosphors Based on the Mn2+ Regulation and Energy Transfer

β-Ca3(PO4)2 type phosphors Ca9Tb(PO4)7:Mn2+ were fabricated by high temperature solid state reaction. Under 377 nm light excitation, the Ca9Tb(PO4)7 host displays the green emission attributable to the characteristic emission of Tb3+ ions peaking at 488, 542, 586, and 620 nm, respectively. The red broadband emission is observed when Ca9Tb(PO4)7 is doped with Mn2+ ions. The emission is attributed to the energy transfer from Tb3+ to Mn2+ ions; this facilitates the realization of the tunable green–red emission. The energy transfer mechanism from Tb3+ to Mn2+ is defined as quadrupole–quadrupole interaction. Furthermore, the thermal stability of Ca9Tb(PO4)7:Mn2+ samples has been studied, and it can maintain half the emission intensity exceeding 424 K. This demonstrates their potential applications in white light LEDs (w-LEDs).

Light converting Yb3+/Er3+ doped YVO4 nanoparticles for biological applications

We have synthesized luminescent YVO4: Yb, Er nanoparticles (NPs) in the size range of 10–700 nm. A bright green luminescence of the dry NPs powder due to Er3+ ions emission centered at 526 and 550 nm was compared for upconverting and downconverting laser excitations at 980 nm and 257 nm, respectively. Moreover, the NPs exhibited bright luminescence in colloidal water solution upon 980 nm laser irradiation. All experiments showed very weak radiative 4F9/2→4I15/2 emission from Er3+ ions at 660 nm that indirectly indicates low efficiency of multiphonon intraionic transitions and insensitivity of the NPs to the luminescence quenchers in the water solution. A broad red band in the luminescence spectrum appearing under intense 257 nm laser excitation can be attributed to emission from crystal lattice defects in the NPs. Based on these facts we propose that YVO4: Yb, Er NPs are promising as efficient upconversion fluorescent nanoprobes for certain biological applications, like optogenetics.

Self-reduction of Yb3+ to Yb2+ and red persistent luminescence of Na2CaGe2O6:Yb2+ phosphor

Phosphors are luminescent materials that are widely used in the lighting and displays of today's world. A reduction-atmosphere is commonly used to synthesize efficient broadband phosphors activated by divalent rare earth ions. In this work, we first report the unusual self-reduction of Yb3+ to Yb2+ in air in Na2CaGe2O6 (NCGO), which shows red broadband persistent luminescence (PersL). The self-reduction effect is revealed to be associated with the appropriate structure of NCGO. On the basis of the investigations, we summarize the basic structural conditions and mechanisms of the self-reduction effect. This important finding will enlighten us to a new approach for designing broadband germanate PersL phosphors. In addition, the PersL properties and mechanisms of the NCGO:Yb2+ phosphors are also investigated.

The formation of massive, quiescent galaxies at cosmic noon

Abstract The cosmic noon (z ∼ 1.5–3) marked a period of vigorous star formation for most galaxies. However, about a third of the more massive galaxies at those times were quiescent in the sense that their observed stellar populations are inconsistent with rapid star formation. The reduced star formation activity is often attributed to gaseous outflows driven by feedback from supermassive black holes, but the impact of black hole feedback on galaxies in the young Universe is not yet definitively established. We analyse the origin of quiescent galaxies with the help of ultrahigh resolution, cosmological simulations that include feedback from stars but do not model the uncertain consequences of black hole feedback. We show that dark matter haloes with specific accretion rates below ∼0.25–0.4 Gyr−1 preferentially host galaxies with reduced star formation rates and red broad-band colours. The fraction of such haloes in large dark matter only simulations matches the observed fraction of massive quiescent galaxies (∼1010–1011 M⊙). This strongly suggests that halo accretion rate is the key parameter determining which massive galaxies at z ∼ 1.5–3 become quiescent. Empirical models that connect galaxy and halo evolution, such as halo occupation distribution or abundance matching models, assume a tight link between galaxy properties and the masses of their parent haloes. These models will benefit from adding the specific accretion rate of haloes as a second model parameter.

Witnessing the transformation of a quasar host galaxy at z = 1.6

A significant minority of high redshift radio galaxy (HzRG) candidates show extremely red broad band colours and remain undetected in emission lines after optical `discovery' spectroscopy. In this paper we present deep GTC optical imaging and spectroscopy of one such radio galaxy, 5C 7.245, with the aim of better understanding the nature of these enigmatic objects. Our g-band image shows no significant emission coincident with the stellar emission of the host galaxy, but does reveal faint emission offset by ~3" (26 kpc) therefrom along a similar position angle to that of the radio jets, reminiscent of the `alignment effect' often seen in the optically luminous HzRGs. This offset g-band source is also detected in several UV emission lines, giving it a redshift of 1.609, with emission line flux ratios inconsistent with photoionization by young stars or an AGN, but consistent with ionization by fast shocks. Based on its unusual gas geometry, we argue that in 5C 7.245 we are witnessing a rare (or rarely observed) phase in the evolution of quasar hosts when stellar mass assembly, accretion onto the back hole, and powerful feedback activity has eradicated its cold gas from the central ~20 kpc, but is still in the process of cleansing cold gas from its extended halo.

Synergy between polar-orbiting and geostationary sensors: Remote sensing of the ocean at high spatial and high temporal resolution

Ocean colour sensors have been capturing the state of the world's oceans for over a decade. They are typically installed on polar-orbiting satellites and cover the entire earth every 1 to 2days. This temporal resolution is insufficient to observe oceanic processes occurring at a higher frequency, especially when taking cloud cover into account. Data from geostationary platforms can be obtained with a much better temporal resolution (images every 15 or 60min), and thus are useful to study those processes. We show that by synergistically combining marine reflectance data from SEVIRI, a geostationary sensor, and MODIS Aqua, a polar orbiter, the resulting product is an improvement over both data sources. The synergy approach takes the reflectance from MODIS, with high quality and high spatial resolution, and modulates this over the day by the temporal variability of the SEVIRI reflectance, normalized to the SEVIRI reflectance at the time of MODIS overpass. The temporal frequency of the synergy product is much better than that of MODIS, and by using the latter's high quality data, the limited spatial and radiometric resolution of SEVIRI is enhanced. As the SEVIRI data is limited to a single broad red band (560–710nm), the applications of the synergy product are limited to parameters that can be derived from this band, such as suspended particulate matter (SPM), turbidity (T) and the diffuse attenuation of photosynthetically available radiation (Kpar) in turbid waters. A geostationary ocean colour sensor over Europe will provide invaluable data concerning our marine environment. The cost of increasing the spatial resolution of a geostationary sensor is very high, and this study illustrates that a lower resolution geostationary ocean colour sensor combined with a high resolution polar orbiting sensor, can provide a high frequency synergetic product with high spatial resolution.

Facile Synthesis of (Sr,Ca)2Si5N8:Eu2+-Based Red-Emitting Phosphor for Solid-State Lighting

A new facile synthetic route to produce a nitride-based red-emitting phosphor has been established. The (Sr,Ca)2Si5N8:Eu2+-based multicomponent phosphor was successfully synthesized from the stable SrCO3–CaCO3–Eu2O3–Si3N4 system by simple one-step heating at 1600 °C for 4 h in an unpressurized N2 atmosphere. The synthesized (Sr,Ca)2Si5N8:Eu2+-based red broadband emitting phosphor exhibited the peak wavelength as long as 661 nm with a practically high external quantum efficiency of 60% under the excitation at 450 nm, while the coexisting secondary phase was inactive under the blue-light excitation, showing no detrimental effects on the photoluminescent properties. The enhanced red emission compared to the unmodified Sr2Si5N8:Eu2+ phosphor enables further improvement of the color rendering properties of the white light-emitting diodes for solid-state lighting applications.

Collision-Induced Dissociation and Infrared Photodissociation Studies of Methane Adsorption on V5O12+ and V5O13+ Clusters

V5O12CH4(+) and V5O13CH4(+) clusters are generated from interactions of pregenerated V5O12(+) and V5O13(+) with CH4 in a fast flow reactor, respectively. The two adsorption complexes are then characterized by collision-induced dissociation (CID) and infrared photodissociation (IRPD) methods. The CID studies indicate that CH4 is molecularly adsorbed on V5O12(+) and V5O13(+). Each of the IRPD spectra of V5O12CH4(+) and V5O13CH4(+) has a broad red band located around 2770 cm(-1) and a narrow blue band located around 2990 cm(-1). The red and blue bands have large and small red shifts with respect to the symmetric and antisymmetric C-H stretch vibrations of free CH4, respectively. Density functional theory calculations are carried out for the structures and vibrational frequencies of V5O12(+) and V5O12CH4(+). The computed results suggest that the anharmonicity including Fermi resonance should be taken into account to interpret the observed IRPD spectrum. In V5O12CH4(+), the CH4 unit adsorbs on the 3-fold coordinated V(5+) site with an η(2) configuration. The stretch of the two C-H bonds close to the V(5+) ion is associated with the red band and the stretch of the other two C-H bonds is associated with the blue band. This study may shed light on the nature of methane adsorption onto vanadium pentoxide surfaces.

Local analysis of Eu2+ emission in CaAlSiN3

We have investigated the local luminescence properties of Eu-doped CaAlSiN3 by using low-energy electron beam (e-beam) techniques. The particles yield broad emission centered at 655 nm with a shoulder at higher wavelength under light excitation, and a broad band around 643 nm with a tail at 540 nm under e-beam excitation. Using cathodoluminescence (CL) in a scanning electron microscope (SEM), we have observed small and large particles, which, although with different compositions, exhibit Eu2+-related emissions at 645 and 635 nm, respectively. Local CL measurements reveal that the Eu2+ emission may actually consist of several bands. In addition to the red broad band, regularly spaced sharp peaks have been occasionally observed. These luminescence variations may originate from a variation in the composition inside CaAlSiN3.

Phosphor Dysprosium‐Doped Layered Double Hydroxides Exchanged with Different Organic Functional Groups

The layers of a Zn/Al layered double hydroxide (LDH) were doped with Dy3+ cations. Among some compositions, the Zn2+ : Al3+ : Dy3+ molar ratio equal to 30 : 9 : 1 presented a single crystalline phase. Organic anions with carboxylic, amino, sulfate, or phosphate functional groups were intercalated as single layers between LDH layers as confirmed by X‐ray diffraction and infrared spectroscopy. Photoluminescence spectra of the nitrate intercalated LDH showed a wide emission band with strong intensity in the yellow region (around 574 nm), originated due to symmetry distortion of the octahedral coordination in dysprosium centers. Moreover, a broad red band emission was also detected apparently due to the presence of zinc oxide. The distorted symmetry of the dysprosium coordination environment, also confirmed by X‐ray photoelectron spectroscopy analysis, was modified after the intercalation with phenyl phosphonate (PP), aspartate (Asp), adipate (Adip), and serinate (Ser) anions; the emission as measured from PL spectra of these LDH was more intense in the blue region (ca. 486 nm), thus indicating an increase in symmetry of dysprosium octahedrons. The red emission band from zinc oxide kept the same intensity after intercalation of dodecyl sulfate (DDS). An additional emission of unknown origin at λ = 767 nm was present in all LDHs.

Tetranuclear d-f Metallostars: Synthesis, Relaxometric, and Luminescent Properties

A novel ditopic ligand DTPA-ph-phen, based on 1,10-phenanthroline and diethylenetriaminepentaacetic acid (DTPA) units, has been designed and fully characterized by (1)H, (13)C, and 2D-COSY NMR spectroscopy, IR and electrospray ionization mass spectrometry (ESI-MS) techniques. The DTPA core of the ligand specifically binds Ln(III) ions (Ln = Eu, Gd) resulting in formation of the [Ln{DTPA-ph-phen}(H(2)O)](-) complex. The photophysical properties of the Eu(III) compound have been investigated, and the complex shows characteristic red luminescence with an overall quantum yield of 2.2%. Reaction of [Gd{DTPA-ph-phen}(H(2)O)](-) with Ru(II) leads to further self-assembly into a heterobimetallic metallostar complex containing Gd(III) and Ru(II) in a 3:1 ratio. This tetranuclear [(Gd{DTPA-ph-phen})(3)(H(2)O)(3)Ru](-) complex (Gd(3)Ru), formed by the coordination of Ru(II) to the 1,10-phenanthroline unit, has been characterized by a range of experimental techniques and evaluated toward its feasibility as a potential bimodal optical/MRI agent. The Gd(3)Ru metallostar shows intense metal-to-ligand charge transfer (MLCT) transition resulting in intense light absorption in the visible spectral region. Upon irradiation into this MLCT band at 450 nm, the Gd(3)Ru complex exhibits red broad-band luminescence in the range of 550-800 nm centered at 610 nm with a quantum yield of 4.8%. Proton nuclear magnetic relaxation dispersion (NMRD) measurements indicate that the Gd(3)Ru complex exhibits an enhanced relaxivity value r(1) of 36.0 s(-1) mM(-1) per metallostar molecule at 20 MHz and 310 K. The ability of the complex to noncovalently bind to human serum albumin (HSA) was investigated, but no significant interaction was detected.

Comparison of thermoluminescence (TL) and cathodoluminescence (ESEM-CL) properties between hydrothermal and metamorphic quartzes

This paper reports on the Thermoluminescence (TL) and Cathodoluminescence (CL) emission of well-characterized hydrothermal milky quartz specimens from Hakkari in Turkey, labeled THQ, and Madrid in Spain, labeled SHQ, and metamorphic quartz from Madrid, in Spain, labeled SMQ. Both hydrothermal and metamorphic quartz samples display similar UV–IR CL spectra consisting of five groups of components centered at 330nm and 380nm linked to [AlO4]° centers, 420nm due to intrinsic defects such as oxygen vacancies, lattice defects, and impurities which modify the crystal structure, 480nm associated with [AlO4]° centers of substitutional Al3+, and a red broad band related to the hydroxyl defects in the quartz lattice as precursors of non-bridging oxygen hole centers (NBOHC) and substitutional point defects. The Turkish quartz specimen exhibits higher CL intensity in the UV region (up to 330nm) than the Spanish specimens probably linked to the presence of Ca (0.95% in THQ and less than 0.1% in SHQ and SMQ). At wavelengths greater than 330nm, SMQ (formed at high pressure 6000bars and temperatures over 500–600°C) shows higher intensity than the hydrothermal (growth at 2000bars and temperatures 200–300°C) samples associated with the formation process. The natural blue TL glow curves of both THQ and SHQ display a weaker TL intensity than the SMQ, attributable to the Al (0.32%), Ti (0.14%), K (0.01%) and Zr (76ppm) content. It is shown that mineralogical formation, crystallinity index and the content of the impurities seem to be the main parameters of influence in the shape intensity of the CL and TL glow curve emission.

Photoluminescence of Nanocrystalline CdS Thin Films Prepared by Chemical Bath Deposition

Nanocrystalline cadmium sulfide (CdS) thin films were prepared using chemical bath deposition in a solution bath containing , , and . The CdS thin films were investigated using X-ray diffraction (XRD), photoluminescence (PL), and Fourier transform infrared spectroscopy (FTIR). The as-deposited CdS thin film prepared at for 60 min had a cubic phase with homogeneous and small grains. In the PL spectrum of the 2,900 A-thick CdS thin film, the broad red band around 1.7 eV and the broad high-energy band around 2.7 eV are attributed to the S vacancy and the band-to-band transition, respectively. As the deposition time increases to over 90 min, the PL intensity from the band-to-band transition significantly increases. The temperature dependence of the PL intensity for the CdS thin films was studied from 16 to 300 K. The and activation energies are obtained by fitting the temperature dependence of the PL intensity. The and are caused by the deep trap and shallow surface traps, respectively. From the FTIR analysis of the CdS thin films, a broad absorption band of the OH stretching vibration in the range and the peak of the CN stretching vibration at were found.

ESR and fluorescence studies of Mn-doped Na 2ZnP 2O 7 single crystal and glasses

X-band electron spin resonance (ESR) spectra and fluorescence measurements were performed on Mn-doped Na 2ZnP 2O 7 (NZPO) single crystal synthesized by the Czochralski pulling method and glasses synthesized by the quenching process. For the single crystal, ESR angular dependences were measured in both the zx and xy plans of the NZPO lattice. The fine and hyperfine structure parameters and g-factor values were determined by modelling the experimental spectra. Using the Newman superposition model, the resonating centres in the single crystal and powder (crushed from crystals) samples are assigned to Mn 2+ ions substituting for both zinc and sodium. For the glass sample the analysis of the ESR data shows that Mn 2+ ions substitute for the Na + ions. These interpretations are confirmed by the fluorescence measurements with a unique broad red band for the glassy compound and the presence of two emission bands (green and red) in the case of the crystal sample.