Broad Emission Band Research Articles

New lead-freeIodoantimonatehalide semiconductor: Synthesis, Structural characterization, DFT calculations, Hirshfeld surface, Thermal behavior, vibrational and optical properties

Hybrid metal halides have captured broad interest in the lighting and display fields because of their unique electronic structures and splendid broadband emission properties. Organic chiral building blocks can control light, charge, and spin interconversion in hybrid crystalline semiconductors with metal-halide.Based on the chiral organic molecules(S)-1-phenylethylamine, we synthesized new chiral antimony halidewith zero-dimensional structure((S)-C8H12N)4Sb2I10. Atroom temperature, the title compound is crystallized in the monoclinic P21with Z = 2 and the following unit cell dimensions: a = 12.69129 (15) Å, b = 14.96770 (15) Å, c = 13.91397 (16) Å, and β = 92.2735 (11)°.The crystal structure of this compound is composed of two crystallographically independent [Sb2I10]4- unit and four (S)-1-phenylethylammonium per unit cell. The crystal packing is governed by NH....I hydrogen bonds.Intermolecular interactions seen in the grown single crystal are studied by Hirshfeld surface and 2-D fingerprint plot.In addition to study the weak interaction a visualized approach known as RDG has been carried out.The recorded infrared IR and Raman studies confirm vibrational modes for organic and inorganic groups at room temperature in the 500–4000 cm−1 and 50–4000 cm−1 frequency regions, respectively.The optimized molecular structure and vibrational frequencies were calculated by the Density Functional Theory (DFT) method using the B3LYP level employing a LANL2DZbasis set.The title compound reveals thermal stability up to 190 °C.The opticalabsorption measurement confirms the semiconductor nature with a band gap of around 3.74 eV. The frontier molecular orbital analysis HOMO-LUMOof molecule were studied.

A physics-guided automated machine learning approach for obtaining surface radiometric temperatures on sunny days based on UAV-derived images

Urban surface radiometric temperatures, approximate to the surface kinetic temperatures, are predominantly retrieved using satellites or unmanned aerial vehicles (UAVs) and exhibit pronounced spatiotemporal variations. Despite numerous methods ranging from empirical to physical models for obtaining urban microscale surface radiometric temperatures via UAVs, challenges remain given the limited physical significance and substantial professional barriers to method application. Against this background, this study introduces a novel and straightforward approach for acquiring spatially distributed radiometric temperatures on sunny days without understanding the complex radiative transfer process as well as acquiring low-altitude atmospheric parameters. An automated machine learning was employed to train a model capable of efficiently estimating radiometric temperatures. Training and testing datasets were created based on the urban radiative transfer equation, incorporating three independent variables: UAV-measured surface brightness temperature, broadband emissivity, and sky view factor, which collectively represent the diverse thermal environments across different surface characteristics and urban layouts during sunny transitional and summer seasons. The model's accuracy was subsequently confirmed through direct comparisons with radiometric temperatures retrieved from UAV-collected multimodal images and kinetic temperatures synchronously collected on the ground across four periods. The results indicate that AutoGluon achieved high accuracy (MAE: 0.04 K; RMSE: 0.06 K; R2: 0.99). Additional ground measurement validations further demonstrated the model's reliability, with absolute biases on sunlit surfaces maintained within 1.25 K. Given its capability for real-time, high-spatial-resolution mapping of radiometric temperatures (April test: 8.70 cm, July test: 6.89 cm) in urban microscales with considerable heterogeneity, such a method is envisioned to be an effective tool for the dynamic monitoring and management of thermal environments at the microscale level in urban settings.

Broadband spectral cyan emission phosphor for full-spectrum LED caused by interstitial site occupation

The phosphor with a highly condensed, rigid framework structure and a single crystallographic site often exhibit symmetrical narrow-band emission. It is challenging to achieve broadband emission by doping Eu2+ ions in similar structures. Here, we propose to control the occupation and quenching concentration of Eu2+ ions in a single-site matrix Sc2Si2O7 to increase efficiency and precise regulation of luminescence spectra substantially. The analysis of photoluminescence spectroscopy through steady-state, transient-state, and Gaussian fitting techniques has discovered two emission centers despite the presence of a single rare-earth substitution site. The theoretical calculations and bond valence sum subsequently prove that Eu2+ ions prefer substituting the Sc3+ and interval sites to emit intense cyan light. Under 340 nm excitation, broad cyan-emission (FWHM = 115 nm) is exhibited with a high quantum yield of 60.67 %. The present phosphor exhibits pronounced thermal stability, and the emission intensity can still keep 68.3 % at 170 °C compared to that at atmospheric temperature. The Sc2Si2O7: Eu2+ phosphor boasts exceptional potential as a highly efficient cyan component in full-spectrum WLEDs. By replacing the blue light component commonly found in WLEDs, the intelligent and healthy alternative Sc2Si2O7: Eu2+ phosphor can effectively decrease the harmful blue light. This work also highlights the critical need to analyze local phosphor distortions upon rare-earth substitution, especially in single crystallographic site structures.

Beyond the Rotational Deathline: Radio Emission from Ultra-long Period Magnetars

ABSTRACT Motivated by the recent detection of ultralong-period radio transients, we investigate new models of coherent radio emission via low-altitude electron–positron pair production in neutron stars (NSs) beyond rotationally powered curvature radiation deathlines. We find that plastic motion (akin to ‘continental drift’) and qualitatively similar thermoelectric action by temperature gradients in the crusts of slowly rotating, highly magnetized NSs could impart mild local magnetospheric twists. Regardless of which mechanism drives twists, we find that particle acceleration initiates pair cascades across charge-starved gaps above a mild critical twist. Cascades are initiated via resonant inverse-Compton scattered photons or curvature radiation, and may produce broad-band coherent radio emission. We compute the pair luminosity (maximum allowed radio luminosity) for these two channels, and derive deathlines and ‘active zones’ in $P-\dot{P}$ space from a variety of considerations. We find these twist-initiated pair cascades only occur for magnetar-like field strengths $B \gtrsim 10^{14}$ G and long periods: $P_{\rm RICS} \gtrsim 120 \,\, (T/10^{6.5} {\rm K})^{-5} \, {\rm s}$ and $P_{\rm curv} \gtrsim 150 \,\, ({\rm v_{\rm pl}}/10^{3} {\, \rm cm \, yr^{-1}})^{-7/6} \, {\rm s}$. Using a simplified geometric model, we find that plastic motion or thermoelectrically driven twists might naturally reproduce the observed luminosities, time-scales, and timing signatures. We further derive ‘active zones’ in which rotationally powered pair creation occurs via resonantly scattered photons, beyond standard curvature deathlines for pulsars. All cascades are generically accompanied by simultaneous (non-)thermal X-ray/UV counterparts which might be detectable with current instrumentation.

New Insights in Luminescence and Quenching Mechanisms of Ag2S Nanocrystals through Temperature-Dependent Spectroscopy.

Bright near-infrared-emitting Ag2S nanocrystals (NCs) are used for in vivo temperature sensing relying on a reversible variation in intensity and photoluminescence lifetime within the physiological temperature range. Here, to gain insights into the luminescence and quenching mechanisms, we investigated the temperature-dependent luminescence of Ag2S NCs from 300 to 10 K. Interestingly, both emission and lifetime measurements reveal similar and strong thermal quenching from 200 to 300 K, indicating an intrinsic quenching process that limits the photoluminescence quantum yield at room temperature, even for perfectly passivated NCs. The low thermal quenching temperature, broadband emission, and multiexponential microsecond decay behavior suggest the optical transition involves strong lattice relaxation, which is consistent with the recombination of a Ag+-trapped hole with a delocalized conduction band electron. Our findings offer valuable insights for understanding the optical properties of Ag2S NCs and the thermal quenching mechanism underlying their temperature-sensing capabilities.

Global Thermospheric Infrared Response to the Mother's Day Weekend Extreme Storm of 2024

AbstractEarth experienced the strongest geomagnetic storm in 20 years over 10–13 May 2024. The Ap and Dst geomagnetic indices were 273 and −291.94 nT on 11 May. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics satellite observed significant enhancement in thermospheric infrared emission at 15, 5.3, 4.3, and 1.27 μm. On 11 May the daily global power radiated by nitric oxide (NO) at 5.3 μm was 1.41 TW and by carbon dioxide (CO2) at 15 μm was 1.35 TW. These are the largest single day power values observed by SABER in 22 years and the first time the daily power radiated by NO exceeded that of CO2. The total infrared power (above background) radiated during the storm was 2.64 TW (2.28 × 1017 J). Significant enhancement in limb radiance observed at 4.3 μm (to 250 km tangent height) is likely indicative of NO + formation during the storm.

Ultrafast Near‐Infrared Luminescence from Cyclometalated Iridium(III) Complexes with Indirubin as Ancillary Ligand

AbstractBeing a constitutional isomer of the indigo dye, indirubin has been known as a purple colourant for a long time. On the other hand, its structural and photophysical properties as ligand in metal complexes are virtually unexplored. Herein, for the first time, we utilized indirubin as ancillary chelator to develop two new heteroleptic iridium(III) complexes equipped with two 2‐phenylpyridine units as archetypical cyclometalating ligands. These new complexes display fully reversible oxidation and reduction processes, and show a panchromatic absorption extending up to 900 nm in acetonitrile solution at 298 K. Moreover, an unexpected broad and unstructured emission band is detected for both complexes in the near‐infrared region, peaking at approx. 1100 nm and having a lifetime of approx. 60 ps; such an emission is attributed to a ligand‐centred triplet excited state (3LC) located on the indirubin ligand itself, as proved by DFT calculations. These findings may pave the way for further exploration of the indirubin dye as a ligand for different types of metal centres to create efficient near‐infrared triplet emitters without the need for difficult synthetic procedures.

Blue-Light-Excitable Red-Emitting Organic Antimony Halides as a Reversible Humidity Sensor.

Zero-dimensional organic antimony halides have attracted significant attention recently due to their structural variety, tunable optical properties, and high luminescence efficiency. Here, a new series of antimony bromide hybrid structures with seesaw [SbBr4] and pyramidal [SbBr5] geometries are reported with low band gaps and blue-light excited red emissions. Their luminescence is attributed to self-trapped excitons with a broadband emission of a large Stokes shift. Their photoluminescence signal is sensitive to water molecules, with a reversible positive correlation in a relative humidity range of 30-90%, enabling them as potential materials for real-time, self-consistent humidity sensors.

Effect of Isopropanol on Optical Properties of Fe3O4/ZnO/Graphene Quantum Dots (GQDs) Nanocomposite

This study aims to investigate the impact of isopropanol on the optical properties of the Fe₃O₄/ZnO/GQDs nanocomposite. The synthesis of Fe₃O₄ and ZnO nanoparticles was conducted using the coprecipitation method, followed by the synthesis of GQDs using the hydrothermal method with varying concentrations of isopropanol. Subsequently, the Fe₃O₄/ZnO nanocomposite was combined with GQDs synthesized using the sonication method. The amalgamation of magnetic and luminescent materials holds promise for applications in the biomedical field, particularly in bioimaging. XRD data analysis revealed crystal structure alterations attributed to the incorporation of carbon elements in both ZnO and Fe₃O₄. The TEM results indicated a particle size of 16.2 nm for the Fe₃O₄/ZnO/GQDs nanocomposite with a 10 ml isopropanol variation. Identified phases from the XRD analysis include Fe₃O₄, ZnO, and GQDs. UV-Vis spectroscopy detected distinctive absorbance peaks at wavelengths of 323.7 nm, 333.0 nm, 329.9 nm, and 323.9 nm. Moreover, the energy gap exhibited an increase with escalating concentrations of isopropanol in the GQDs. Photoluminescence analysis yielded robust, broad emission bands characterized by orange and red luminescence.

Temperature retrieval of near space with the combined use of O2(a1Δg) and O2(b1∑+ g) dayglow emissions under self-absorption effect correction

Atmospheric temperature information in the near space is of great academic significance and engineering value to support the development and utilization of the near space. Based on the theory of O2 molecular dayglow spectroscopy and the mechanism of atmospheric radiative transfer, a method is proposed for the joint retrieval of temperature profiles in the near space using O2(a1Δg) and O2(b1∑+g) bands dayglow spectroscopy signal with the self-absorption effect. First, the temperature dependence of O2(a1Δg) and O2(b1∑+g) bands dayglow is investigated, and the influence of the self-absorption effect on the radiative transfer characteristics is analyzed in the limb-view mode. Then, with the use of the onion peeling algorithm, the dayglow emission spectra signals of the O2(a1Δg) and O2(b1∑+g) bands measured by the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) in the limb-viewing mode were processed, and combined with optimization algorithms, the temperature profiles from 35 km to 120 km is successfully retrieved. Finally, the accuracy and reliability of the self-absorption effect correction as well as the joint temperature retrieval were verified by comparing with temperature product data from remote sensing satellites such as Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), Atmospheric Chemistry Experiment Fourier-Transform Spectrometer (ACE-FTS), and Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). The error analysis shows that the temperature retrieval error after correction for the self-absorption effect is about 3 K minimum and 20 K maximum.

Antimicrobial photodynamic therapy against Escherichia coli by exploiting endogenously produced Protoporphyrin IX- In vitro study.

Due to antimicrobial drug resistance, there is a growing interest in the development of light based alternative antibacterial therapies. This research work is focused on the inactivation of Escherichia coli (E. coli) by exploiting the absorption bands 405, 505, 542, 580 and 631nm of its indigenously produced Protoporphyrin IX (PpIX) excited by three LEDs with broad emission bands at 418, 522 and 630nm and two laser diodes with narrow emission bands at 405 and 635nm. Fluorescence spectroscopy and plate count method have been employed for studying the inactivation rate of E. coli strain in autoclaved water suspension. It has been found that LEDs at 418, 522 and 630nm produced pronounced antimicrobial photodynamic effect on E. coli strain comparing laser diodes at 405 and 635nm, which might be attributed to the overlapping of broad emission bands of LEDs with the absorption bands of PpIX than narrow emission bands of laser diodes. Particular effect of LED at 522nm has been noticed because its broad emission band overlaps three absorption bands 505, 542 and 580nm of PpIX. The gold standard plate count method strongly correlates with Fluorescence spectroscopy, making it an innovative tool to administer bacterial inactivation. The experimental results suggested the development of a light source that entirely overlap absorption bands of PpIx to produce a pronounced antimicrobial photodynamic effect, which might become an effective modality for in vivo disinfection of antibiotic resistant microbes in wounds and lesions.

Room temperature luminescence of 1,N2-etheno-2-aminopurine in poly (vinyl alcohol) films.

We studied spectral properties of 1,N2-etheno-2-aminopurine after immobilization in poly (vinyl alcohol) films. The absorption spectrum of 1,N2-ε2APu consists of two peaks centered at 300 and 370 nm, and the fluorescence spectrum has maximum at about 460 nm. The fluorescence quantum efficiency is 62%. The fluorescence anisotropy reaches a value of 0.3 at longer wavelengths, while it is low at shorter wavelengths (corresponding to the second single excited state). The 1,N2-ε2APu has a relatively long fluorescence lifetime of about 16 ns and a noticeable room temperature phosphorescence with a lifetime of about 220 ms. A broad phosphorescence emission band (425-675 nm) is centered at about 530 nm and markedly overlaps with fluorescence at shorter wavelengths. Surprisingly, the phosphorescence excitation spectrum of 1,N2-ε2APu-doped poly (vinyl alcohol) film differs from the absorption and fluorescence excitation spectra. The strongest room temperature phosphorescence excitation is about 335 nm. At longer excitation wavelengths, above 450 nm, where fluorescence cannot be excited, a triplet excitation is still possible. The 1,N2-ε2APu phosphorescence anisotropy spectra confirm direct triplet state excitation. The ability to excite molecules at long wavelengths can find applications in the study of biological molecules that are unstable when excited at high energies.

Impacts of Eu2+ -doped K3LuSi2O7 phosphor and a scattering particle on conventional white light emitting diodes

The K<sub>3</sub>LuSi<sub>2</sub>O<sub>7</sub> phosphor doping Eu2+ rare-earth ions (KLS:Eu) was reported to possess broad emission band from near-ultraviolet to nearinfrared. Additionally, this phosphor showed a wide absorption band of 250-600 nm, allowing it to be excited by blue-light chip of 460 nm, making it one of the suitable phosphor materials for a light emitting diode (LED). Besides, the scattering particle material CaCO<sub>3</sub> is incorporated into the yellow phosphor layer to serve the scattering-enhancement purpose. The combination of both materials aims at accomplishing improvements in performance of commercial LED package. The concentration of KLS:Eu is constant while that of CaCO3 is modified. As a result, the scattering factor is regulated and become the key factor influencing the optical outputs of the simulated LED. The increasing CaCO<sub>3</sub> concentration enhances the phosphor scattering efficiency of light, helping to improve the lumen output and color-temperature consistency of the LED. However, the color rendering performance declines as a function of the CaCO3 growing amount, despite the presence of a KLS:Eu phosphor layer. Further works should be done to optimize the application of KLS:Eu in cooperation with scattering particles for a higher-quality LED device.

Modeling Blazar Broadband Emission with Convolutional Neural Networks. II. External Compton Model

In the context of modeling spectral energy distributions (SEDs) for blazars, we extend the method that uses a convolutional neural network (CNN) to include external inverse Compton processes. The model assumes that relativistic electrons within the emitting region can interact with and up-scatter external photons originating from the accretion disk, the broad-line region, and the torus, to produce the observed high-energy emission. We trained the CNN on a numerical model that accounts for the injection of electrons, their self-consistent cooling, and pair creation-annihilation processes, considering both internal and all external photon fields. Despite the larger number of parameters compared to the synchrotron self-Compton model and the greater diversity in spectral shapes, the CNN enables an accurate computation of the SED for a specified set of parameters. The performance of the CNN is demonstrated by fitting the SED of two flat-spectrum radio quasars, namely 3C 454.3 and CTA 102, and obtaining their parameter posterior distributions. For the first source, the available data in the low-energy band allowed us to constrain the minimum Lorentz factor of the electrons, γmin , while for the second source, due to the lack of these data, γmin=102 was set. We used the obtained parameters to investigate the energetics of the system. The model developed here, along with one from Bégué et al., enables self-consistent, in-depth modeling of blazar broadband emissions within a leptonic scenario.

Impact of interplanetary shock on nitric oxide cooling emission: A superposed epoch study

The impact of interplanetary (IP) shock on Nitric Oxide (NO) 5.3 µm cooling emission is studied during geomagnetic quiet periods. The Active Magnetosphere and Planetary Electrodynamics Response Experiment measurements of field-aligned-currents intensify during IP shock with a relatively higher magnitude in southern hemisphere as compared to the northern hemispheric counterpart. The Defense Meteorological Satellite Program spacecraft observations displayed an early and strong enhancement in the precipitating particle flux of energy less than 1 keV. The particle flux of higher energy responds at later time. The NO density exhibited a significant, pre-event increase by an order of magnitude due to low-energy particle precipitation. The thermospheric temperature increased by about 100 K at 400 km. The superposed epoch analysis study revealed a linear enhancement in SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) measurements of NO cooling emission onboard the TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics) satellite due to the prompt increase in particle precipitations and thermospheric temperature triggered by IP shock.

Preparation, structure, and property evolution of transparent germanate glass-ceramics based on a new strategy: One-step heat treatment around Tg

In this work, Cr3+ ion introduced germanate transparent glass-ceramics with one-step heat treatment around the glass transition temperature were prepared. By using TEM and other structural characterizations, it was demonstrated that the microstructure of glass-ceramics had uniform distribution and excellent grain development. Through XPS, FTIR, Raman and JMA model calculation, it was found that the substitution of Cr2O3 for Ga2O3 led to the decrease of [TO4] ratio in the glass network, and the crystallization behavior changed to the whole crystallization. The results of optical performance tests indicated that the transmittance of the transparent glass-ceramics with one-step heat treatment was 46 % higher than that of glass-ceramics prepared by the two-step heat treatment, and the broadband emission intensity at 980 nm was 1.69 times higher than that of the basic glass. There is some guiding relevance to the innovative preparation approach suggested in this work for the creation of transparent glass-ceramics.

Investigation of the long-term variation of gravity waves over South America using empirical orthogonal function analysis

The spatial and temporal variability of gravity waves (GWs) potential energy (Ep) over South America (SA) was examined by analyzing temperature profiles obtained through the utilization of Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) from January 2002 to December 2021. We used the empirical orthogonal function (EOF) analysis to decompose GWs parameters and to analyze the GW variations over SA. We considered the first three eigenmodes (EOF1, EOF2, and EOF3) and their principal components (PC1, PC2, and PC3) of the EOF decomposition, which accounts for ∼80–90% of the total GWs variation over SA. Further, we analyzed the coupled variation of Ep and zonal mean wind (U) to verify their inter-dependencies using the singular value decomposition (SVD). The spatial variation showed that different localized mechanisms generate GWs at different sectors of the continent. The EOF1 of Ep comprised more than 50%, the EOF2 ∼20–25%, and the third ∼10–15% of the total GWs variation. The positive variation of GWs energy in the EOF1 is localized in the tropical region from the lower stratosphere to the lower mesosphere and southward below 1.5° S in the upper mesosphere. The spectral analysis of GWs energy showed biannual, annual, semiannual, and 11-year variations at different eigenvectors. Relative Ep (REp) showed an asymmetric hemispheric response to solar flux over South America. The REp response to QBO showed a modulating effect below 70 km and a positive response above 70 km. There is a good positive correlation between the temporal component of EOF2 of Ep and the quasi-biennial oscillation (QBO) at 30 mb and 50 mb in the PC2 temporal variation.Graphical

Remarkable broadband NIR emission of BaCa2MgSi2O8:Cr3+ phosphors and Eu2+ co-doping modulation

Developing high-performance broadband NIR (near-infrared) phosphors remains a crucial pursuit for the next-generation smart NIR light source. This study demonstrates the successful synthesis of BaCa2MgSi2O8:Cr3+ phosphors exhibiting exceptional broadband NIR emission via a high-temperature solid-state reaction. Notably, the 0.03Cr3+ doped composition, under 485 nm excitation, shines with a remarkable broadband emission spanning 700 nm–1100 nm and boasts a full width at half maximum (FWHM) of 134 nm. This work meticulously explores the intricate interplay between Cr3+ doping concentration, temperature, crystal field strength, and the Huang-Rhys parameter, shedding light on the underlying luminescence mechanisms. Moreover, the BaCa2MgSi2O8:0.03Cr3+ phosphor exhibits exceptional thermal stability, retaining approximately 70 % of its integrated emission intensity at 425 K compared to room temperature. To further expand the excitation range, Eu2+ was introduced as a co-dopant, successfully broadening the excitation spectrum to encompass nearly the entire ultraviolet–visible region (ranging from 250 nm to 750 nm). The presence of Eu2+→Cr3+ energy transfer was elucidated, and the impact of Eu2+ doping was thoroughly investigated. Moreover, the synthesized phosphor has been successfully integrated into a NIR phosphor-converted light-emitting diode (pc-LED), showcasing their potential application in the realms of night vision and NIR vascular imaging. These findings offer invaluable insights into Cr3+ luminescence behavior and pave the way for the development of novel NIR phosphors with enhanced functionalities, propelling us closer to the realization of next-generation smart lighting solutions.

Ni2+ activated broadband near-infrared II germanate phosphor for pc-LED applications

The broadband near-infrared (NIR) pc-LED is considered as a new generation of light source for substance measurements based on NIR spectroscopy. The most studied Cr3+ doped broadband NIR phosphors emit in the near-infrared I region. However, there is a demand for broadband near-infrared II solid-state light sources for expanding the variety of detected substances. Herein, Ni2+ activated NIR II Mg14Ge5O24 phosphor is synthesized by high-temperature solid-state method. The phosphor shows a asymmetric broad NIR emission band peaked at 1420 nm, that is assigned to the 3T2(3F)→3A2(3F) transition of Ni2+. It is observed that the asymmetric emission band is contributed from two Ni2+ centers, Ni2+(I) and Ni2+(II), occupying Ge4+ site with the emission peaked at 1313 nm and Mg2+ site with the emission peaked at 1435 nm, respectively. It is found that the addition of Ti4+ and B3+ can significantly change the intensity ratio of the two Ni2+ centers and enhance the overall emission intensity. Moreover, the addition of Mn4+ results in only Ni2+(II) emission. The origin of the unique features mentioned above is discussed. The temperature dependence of the NIR emissions is also studied. Finally a broadband NIR II pc-LED with a moderate electro-optical conversion efficiency of 1.4 % is fabricated based on a 400 nm LED chip. The results indicate that the modified Mg14Ge5O24:Ni2+ is a potential broadband NIR II phosphor for pc-LED applications.

Tailoring emission characteristics of Na+-Sc3+ co-substituted CaMgGe2O6:Cr3+ phosphors for iris acquisition

The growing interest in Cr3+-doped broadband infrared phosphors stems from their promising applications in various fields. However, achieving highly efficient broadband emission based on these materials remains a significant challenge. To address this issue, we proposed a cation co-substitution method to enhance the near-infrared (NIR) emission of Cr3+-doped phosphors while simultaneously broadening the full width at half maximum (FWHM) of their emission peaks, as demonstrated in the case of CaMgGe2O6:Cr3+. Through controlled co-substitution of Ca2+ and Mg2+ cations by Na+ and Sc3+ cations, we prepared (Ca, Mg)1-x(Na, Sc)xGe2O6:Cr3+ (CMSxG:Cr3+) using a solid reaction method. This approach aims to deliberately adjust the strength of the crystal field experienced by Cr3+ to regulate the luminescence performance of the corresponding phosphors. Indeed, we observed a red shift of the emission peak from 850 to 902 nm, with the FWHM extending from 163 to 198 nm, as the concentration of ‘Na+-Sc3+’ pair increased, which would benefit iris acquisition. Importantly, the external quantum yield did not deteriorate; instead, it was enhanced from 13.6 to 26.2 %. Finally, we fabricated a broadband near infrared phosphor converted light-emitting diodes (pc-LED) by integrating CMSxG:Cr3+ phosphors with commercial 460 nm LEDs. An infrared output power of 118.01 mW at 300.00 mA was achieved with pc-LED based on Ca0.9Mg0.88(NaSc)0.1Ge2O6:0.02Cr3+ phosphor. Clear iris images acquired using these pc-LED as lighting sources demonstrate their potential applications in iris acquisition for biometrics.