Search

Near-infrared (NIR) emitting phosphors draw much attention because they show great applicability and development prospects in many fields. Herein, a series of inverse spinel-type structured LiGa 5 O 8 phosphors with a high concentration of Cr 3+ activators is reported with a dual emission band covering NIR-I and II regions. Except for strong ionic exchange interactions such as Cr 3+ -Cr 3+ and Cr 3+ clusters, an intervalence charge transfer (IVCT) process between aggregated Cr ion pairs is proposed as the mechanism for the ~1210 nm NIR-II emission. Comprehensive structural and luminescence characterization points to IVCT between two Cr 3+ being induced by structural distortion and further enhanced by irradiation. Construction of the configurational energy level diagram enabled elucidation of this transition within the IVCT process. Therefore, this work provides insight into the emission mechanism within the high Cr 3+ concentration system, revealing a new design strategy for NIR-II emitting phosphors to promote its response., (© 2024 Wiley-VCH GmbH.)

The minimization of thermal quenching, which leads to luminescence loss at high temperatures, is one of the most important issues for near-infrared phosphors. In the present work, we investigated the properties of near-infrared Ca(Sc,Mg)(Al, Si)O 6  : Cr 3+ phosphors with a pyroxene-type structure under blue light excitation. The CaScAlSiO 6  : Cr 3+ end member of Ca(Sc,Mg)(Al,Si)O 6  : Cr 3+ phosphor led to broadband emission at a full-width half maximum of 215 nm, whereas the CaMgSi 2 O 6  : Cr 3+ end member exhibited high thermal stability at 150 °C, with an intensity of 88.4 % of that at room temperature. The structural analysis and density functional theory calculations revealed the absence of soft conformations and local space confinement contributed to the high structural rigidity and weakened the thermal quenching effect., (© 2022 Wiley-VCH GmbH.)

Light-harvesting and conversion ability is important to promote plant growth, and especially when resources are limited. A near-infrared (NIR) nanophosphor embedded with mesoporous silica nanoparticles (MSN), ZnGa 2 O 4 :Cr 3+ ,Sn 4+ (ZGOCS), was developed and its optical properties were harnessed to enhance the photosynthetic ability of Brassica rapa spp. chinensis. The broad excitation of ZGOCS from the ultraviolet to the visible region allowed the conversion of extra light into near-infrared light (650-800 nm) and thus promoted the dual photosystem via the Emerson effect. ZGOCS@MSN was spherical with a size of 65±10 nm and good dispersion. A light conversion ability of up to 75 % under different wavelengths was achieved. Moreover, the electron transfer rate of photosynthesis increased by 100 % with a suitable ZGOCS@MSN concentration. Plant and animal models were used to explore the effects of the nanophosphor. ZGOCS@MSN distribution was tracked by monitoring its NIR emission in plant and animal tissues, demonstrating that this nanophosphor can be potentially utilized in plant growth., (© 2021 Wiley-VCH GmbH.)

A solvent-vapor transport route produces centimeter-sized single-crystal red phosphors. The epitaxial growth route to yield its core-shell structure at ambient temperature was adopted. These red phosphors could be applied in all-inorganic WLED devices. Cs 2 TiF 6 :Mn 4+ (CTFM) single crystal provides enhancement of quantum efficiency, moisture resistance, and thermal stability compared to polycrystalline powders. The internal quantum efficiency can reach as high as 98.7 %. To further improve waterproof stability, the Cs 2 TiF 6 (CTF) shell with tunable thickness has been epitaxially grown on the CTFM single crystal surface and a unique three-step photoluminescence intensity evolution mechanism has been proposed. By combining as-prepared CTFM@CTF core-shell structured single crystal, YAG:Ce single crystal and blue-chip, warm WLEDs with excellent color rendition (R a =90, R 9 =94), low correlated color temperature (CCT=3155 K), and high luminous efficacy were fabricated without any organic resins., (© 2020 Wiley-VCH GmbH.)

In this study, a series of Sr(LiAl 3 ) 1-x (SiMg 3 ) x N 4 :Eu 2+ (SLA-SSM) phosphors were synthesized by a solid-solution process. The emission peak maxima of SLA-SSM range from 615 nm to 680 nm, which indicates structural differences in these materials. 7 Li solid-state NMR spectroscopy was utilized to distinguish between the Li(1)N 4 and Li(2)N 4 tetrahedra in SLA-SSM. Differences in the coordination environments of the two Sr sites were found which explain the unexpected luminescent properties. Three discernible morphologies were detected by scanning electron microscopy. Temperature-dependent photoluminescence and decay times were used to understand the diverse environments of europium ions in the two strontium sites Sr1 and Sr2, which also support the NMR analysis. Moreover, X-ray absorption near-edge structure studies reveal that the Eu 2+ concentration in SLA-SSM is much higher than that in in SrLiAl 3 N 4 :Eu 2+ and SrSiMg 3 N 4 :Eu 2+ phosphors. Finally, an overall mechanism was proposed to explain the how the change in photoluminescence is controlled by the size of the coordinated cation., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Light-emitting diodes break barriers of size and performance for displays. With devices becoming smaller, the materials also need to get smaller. Chromium(III)-doped oxide phosphors, which emit near-infrared (NIR) light, have recently been used in small electronic devices. In this work, mesoporous silica nanoparticles were used as nanocarriers. The nanophosphor ZnGa 2 O 4 :Cr 3+ ,Sn 4+ formed in the mesopore after sintering. Good dispersity and morphology were performed with average diameters of 71±7 nm. It emitted light at 600-850 nm; the intensity was optimized by tuning the doping ratio of Cr 3+ and Sn 4+ . Meanwhile, the light conversion efficiency increased from 7.8 % to 37 % and the molar concentration increased from 0.125 m to 0.5 m. The higher radiant flux of 3.3 mW was obtained by operating an input current of 45 mA. However, the NIR nanophosphor showed good performance on mini light-emitting diode chips., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Mn 4+ -doped fluoride phosphors have been widely used in wide-gamut backlighting devices because of their extremely narrow emission band. Solid solutions of Na 2 (Si x Ge 1-x )F 6 :Mn 4+ and Na 2 (Ge y Ti 1-y )F 6 :Mn 4+ were successfully synthesized to elucidate the behavior of the zero-phonon line (ZPL) in different structures. The ratio between ZPL and the highest emission intensity υ 6 phonon sideband exhibits a strong relationship with luminescent decay rate. First-principles calculations are conducted to model the variation in the structural and electronic properties of the prepared solid solutions as a function of the composition. To compensate for the limitations of the Rietveld refinement, electron paramagnetic resonance and high-resolution steady-state emission spectra are used to confirm the diverse local environment for Mn 4+ in the structure. Finally, the spectral luminous efficacy of radiation (LER) is used to reveal the important role of ZPL in practical applications., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

All inorganic CsPbBr 3 perovskite quantum dots (QDs) are potential emitters for electroluminescent displays. We have developed a facile hot-injection method to partially replace the toxic Pb 2+ with highly stable Sn 4+ . Meanwhile, the absolute photoluminescence quantum yield of CsPb 1-x Sn x Br 3 increased from 45 % to 83 % with Sn IV substitution. The transient absorption (TA) exciton dynamics in undoped CsPbBr 3 and CsPb 0.67 Sn 0.33 Br 3 QDs at various excitation fluences were determined by femtosecond transient absorption, time-resolved photoluminescence, and single-dot spectroscopy, providing clear evidence for the suppression of trion generation by Sn doping. These highly luminescent CsPb 0.67 Sn 0.33 Br 3 QDs emit at 517 nm. A device based on these QDs exhibited a luminance of 12 500 cd m -2 , a current efficiency of 11.63 cd A -1 , an external quantum efficiency of 4.13 %, a power efficiency of 6.76 lm w -1 , and a low turn-on voltage of 3.6 V, which are the best values among reported tin-based perovskite quantum-dot LEDs., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A SrLiAl3 N4 :Eu(2+) (SLA) red phosphor prepared through a high-pressure solid-state reaction was coated with an organosilica layer with a thickness of 400-600 nm to improve its water resistance. The observed 4f(6) 5d→4f(7) transition bands are thought to result from the existence of Eu(2+) at two different Sr(2+) sites. Luminescence spectra at 10 K revealed two zero-phonon lines at 15377 (for Eu(Sr1)) and 15780 cm(-1) (for Eu(Sr2)). The phosphor exhibited stable red emission under high pressure up to 312 kbar. The configurational coordinate diagram gave a theoretical explanation for the Eu(2+/3+) result. The coated samples showed excellent moisture resistance while retaining an external quantum efficiency (EQE) of 70 % of their initial EQE after aging for 5 days under harsh conditions. White-light-emitting diodes of the SLA red phosphor and a commercial Y3 Al5 O12 :Ce(3+) yellow phosphor on a blue InGaN chip showed high color rendition (CRI=89, R9=69) and a low correlated color temperature of 2406 K., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

All-inorganic CsPbX3 (X=I, Br, Cl) perovskite quantum dots (PQDs) have been investigated because of their optical properties, such as tunable wavelength, narrow band, and high quantum efficiency. These features have been used in light emitting diode (LED) devices. LED on-chip fabrication uses mixed green and red quantum dots with silicone gel. However, the ion-exchange effect widens the narrow emission spectrum. Quantum dots cannot be mixed because of anion exchange. We address this issue with a mesoporous PQD nanocomposite that can prevent ion exchange and increase stability. We mixed green quantum-dot-containing mesoporous silica nanocomposites with red PQDs, which can prevent the anion-exchange effect and increase thermal and photo stability. We applied the new PQD-based LEDs for backlight displays. We also used PQDs in an on-chip LED device. Our white LED device for backlight display passed through a color filter with an NTSC value of 113 % and Rec. 2020 of 85 %., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A facile approach for coating red fluoride phosphors with a moisture-resistant alkyl phosphate layer with a thickness of 50-100 nm is reported. K2 SiF6 :Mn(4+) particles were prepared by co-precipitation and then coated by esterification of P2 O5 with alcohols (methanol, ethanol, and isopropanol). This route was adopted to encapsulate the prepared phosphors using transition-metal ions as cross-linkers between the alkyl phosphate moieties. The coated phosphor particles exhibited a high water tolerance and retained approximately 87 % of their initial external quantum efficiency after aging under high-humidity (85 %) and high-temperature (85 °C) conditions for one month. Warm white-light-emitting diodes that consisted of blue InGaN chips, the prepared K2 SiF6 :Mn(4+) phosphors, and either yellow Y3 Al5 O12 :Ce(3+) phosphors or green β-SiAlON: Eu(2+) phosphors showed excellent color rendition., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Development of a solar water splitting device requires design of a low-cost, efficient, and non-noble metal compound as alternative to noble metals. For the first time, we showed that CoSe2 can function as co-catalyst in phototoelectrochemical hydrogen production. We designed a heterostructure of p-Si and marcasite-type CoSe2 for solar-driven hydrogen production. CoSe2 successively coupled with p-Si can act as a superior photocathode in the solar-driven water splitting reaction. Photocurrents up to 9 mA cm(-2) were achieved at 0 V vs. reversible hydrogen electrode. Electrochemical impedance spectroscopy showed that the high photocurrents can be attributed to low charge transfer resistance between the Si and CoSe2 interfaces and that between the CoSe2 and electrolyte interfaces. Our results suggest that this CoSe2 is a promising alternative co-catalyst for hydrogen evolution., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)