Efficient Luminescence from CsPbBr₃ Nanoparticles Embedded in Cs₄PbBr₆

This work was financially supported by the “Advanced Research Center of Green Materials Science and Technology” from The Featured Area Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education (107L9006) and the Ministry of Science and Technology in Taiwan (MOST 107-2113-M-002-008-MY3, MOST 107-2923-M-002-004-MY3, and MOST 107-3017-F-002-001), the National Centre for Research and Development Poland Grant (No. PL-TW/V/1/2018), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB20000000), the CAS/SAFEA International Partnership Program for Creative Research Teams, and the NSFC (Nos. U1805252 and 11774345). J.P.A. acknowledges financial support from EPSRC, U.K.Cs4PbBr6 is regarded as an outstanding luminescent material with good thermal stability and optical performance. However, the mechanism of green emission from Cs4PbBr6 has been controversial. Here we show that isolated CsPbBr3 nanoparticles embedded within a Cs4PbBr6 matrix give rise to a “normal” green luminescence while superfluorescence at longer wavelengths is suppressed. High-resolution transmission electron microscopy shows that the embedded CsPbBr3 nanoparticles are around 3.8 nm in diameter and are well-separated from each other, perhaps by a strain-driven mechanism. This mechanism may enable other efficient luminescent composites to be developed by embedding optically active nanoparticles epitaxially within inert host lattices.PostprintPeer reviewe

Photoelectron spectroscopy of a series of acetate and propionate esters

The electronic state and photoionization spectroscopy of a series of acetate esters: methyl acetate, isopropyl acetate, butyl acetate and pentyl acetate as well as two propionates: methyl propionate and ethyl propionate, have been determined using vacuum-ultraviolet photoelectron spectroscopy. These experimental investigations are complemented by ab initio calculations. The measured first adiabatic and vertical ionization energies were determined as: 10.21 and 10.45 eV for methyl acetate, 9.99 and 10.22 eV for isopropyl acetate, 10.07 and 10.26 eV for butyl acetate, 10.01 and 10.22 eV for pentyl acetate, 10.16 and 10.36 eV for methyl propionate and 9.99 and 10.18 eV for ethyl propionate. For the four smaller esters vibrational transitions were calculated and compared with those identified in the photoelectron spectrum, revealing the most distinctive ones to be a C–O stretch combined with a C[dbnd]O stretch. The ionization energies of methyl and ethyl esters as well as for a series of formates and acetates were compared showing a clear dependence of the value of the ionization energy on the size of the molecule with very little influence of its conformation

Control of luminescence by tuning of crystal symmetry and local structure in Mn4+-activated narrow band fluoride phosphors

This work was supported by the Ministry of Science and Technology of Taiwan (Contract Nos. MOST 104-2113-M-002-012-MY3 and MOST 104-2923-M-002-007-MY3) and National Center for Research and Development Poland Grant (No. PL-TW2/8/2015). Y Jin thanks the National Nature Science Foundation of China (No. 11104366), Chongqing Research Program of Basic Research and Frontier Technology (No. cstc2014jcyjA50018), and the Scientific and Technological Research Program of Chongqing Municipal Education Commission (No. KJ1500913). T. Lesniewski would like to acknowledge the support of University of Gdansk Research Grant 538-5200-B468-17.Mn4+-doped fluoride phosphors have been widely used in wide-gamut backlighting devices because of their extremely narrow emission band. In this study, solid solutions of Na2(SixGe1-x)F6:Mn4+ and Na2(GeyTigros)F6:Mn4+ have been successfully synthesized to elucidate the behavior of zero-phonon line (ZPL) in different structures because of the sensitivity of ZPL intensity to the local coordinated environment. The structures of the products are examined by X-ray diffraction and Rietveld refinement. The ratio between ZPL and the highest emission intensity υ6 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. The calculated results are consistent with the experimentally determined structural parameters. To compensate for the limitations of Rietveld refinement, electron paramagnetic resonance and high-resolution steady-state emission spectra are used to prove the diverse local environment for Mn4+ in the structure. Finally, the spectral luminous efficacy of radiation (LER) is used to reveal the important role of ZPL in practical application.PostprintPeer reviewe

Controlling of structural ordering and rigidity of β-SiAlON:Eu through chemical cosubstitution to approach narrow-band-emission for light-emitting diodes application

The authors are grateful for the financial support of the Ministry of Science and Technology of Taiwan (Contract Nos. MOST 104- 2113-M-002-012-MY3, MOST 104-2119-M-002-027-MY3 and 104-2923-M-002-007-MY3) and Australia Research Council (ARC, FT160100251). The contribution of A. L. was supported by the grant “Preludium” UMO-2014/13/N/ST3/03781 from the National Science Center. The contribution of S. M. was supported by the grant “Iuventus Plus” 0271/IP3/2015/73 from the Ministry of Science and Higher Education. M. G. was supported by Polish National Center for Research and Development with grants no PBS3/A5/48/2015 and PL-TWII/8/2015.Narrow-band green-emitting phosphor β-SiAlON:Eu has been widely used in advanced wide-gamut backlighting de- vices. However, the origins for unusual sharp lines in photoluminescence emission at room temperature and tunable narrow-band- emission tailored by reducing Al-O in β-SiAlON:Eu are still unclear. Here, the presence of sharp-line fine structure in the emission spectra of β-SiAlON:Eu is mainly due to purely electronic transitions (zero phonon lines) and their vibronic repetitions resulted from the multi-microenvironment around Eu2+ ions that has been revealed by relative emission intensity of sharp line depends on excitation wavelength and monotonously increasing decay time. The specific features of the Eu2+ occupying interstitial sites indicate that the effect of crystal field strength can be neglected. Therefore the enhanced rigidity and higher ordering structure of β-SiAlON:Eu with decreasing the substitution of Si–N by Al–O become the main factors in decreasing electron–lattice coupling and reducing inhomo- geneous broadening, favouring the blue-shift and narrow of the emission band, the enhanced thermal stability, as well as the charge state of Eu2+. Our results provide new insights for explaining the reason for narrow-band-emission in β-SiAlON:Eu, which will deliver an impetus for the exploration of phosphors with narrow band and ordering structure.PostprintPeer reviewe

Luminescence Properties of LaAlO₃:Pr under Hydrostatic Pressure

The article presents the results of measuring the luminescence spectra, luminescence excitation spectra and luminescence spectra under high pressures for LaAlO3:Pr with concentration of 1%. The materials were synthesized by solid phase synthesis. Diffraction pattern is fully relates to LaAlO3 phase. The photoluminescence spectra show the main energy transitions. The change in the position of the main bands under the hydrostatic pressure of 23, 55, 160 and 191 kBar was demonstrated. The main band at 491 nm is slightly red-shifted, while the line at 605 nm is shifted to the high-energy part of the spectrum. The intensity of all bands increases with increasing hydrostatic pressure. The dynamics of changes in the intensities of maxima and emissions from different transitions are analyzed. Studies of luminescence under high hydrostatic compression are important in observing changes in the internal structure and electronic states of materials under the influence of high pressure, studying internal processes such as recombination of electrons and holes, transitions between energy levels and the release of photons. Understanding the changes that occur under compression can help researchers develop new materials with unique properties

Hydrogen-Containing Na3HTi1- xMnxF8 Narrow-Band Phosphor for Light-Emitting Diodes

We synthesize the phosphor Na3HTi1-xMnxF8 (Na3HTiF8:Mn4+) material series using a coprecipitation method. We determine the complete phase and crystallographic structure of the Na3HTiF8 series end-member, including the determination of the H atoms at the 4b (0, 1/2, 0) crystallographic site within the Cmcm space group symmetry structure, resulting in a quantum efficiency of ∼44%, which is comparative to the Na2SiF6:Mn4+ phosphor materials. We successfully model the luminescent properties of the Na3HTi1-xMnxF8 material series, including temperature and time-dependent photoluminescence, providing a good prediction of the decay properties at low and high temperature and revealing the existence of Mn5+ during the ionization process. Notably, LED package data indicates that the Na3HTi1-xMnxF8 material series could be a promising candidate for high-level and back-lighting devices. This research reveals the role that hydrogen plays in determining fluoride phosphor structure and properties, revealing a new path for the synthesis of fluoride phosphors

Ultra-Broadband Phosphors Converted Near-Infrared Light Emitting Diode with Efficient Radiant Power for Spectroscopy Applications

Copyright © 2019 American Chemical Society. Narrowing the size of near-infrared (NIR) spectrometers has gained substantial interest among researchers in both scientific and nonscientific communities due to the inherent usage in the nondestructive investigations, especially for foodstuff evaluation and human health monitoring. The immense size and deteriorating accessibility of traditional NIR light sources make the phosphor-converted NIR light-emitting diode (pc-NIR LED) with high radiant flux an alternative growing light source. In this work, the crystal structure of La3GaGe5O16 is solved for the actual crystallographic sites through a joint Rietveld refinement tool (X-ray diffraction and high-resolution neutron powder diffraction) and reporting for the ultrabroadband NIR luminescence (650-1050 nm) by doping with Cr3+ with the hyper-radiant power of 43.1 mW. It is noteworthy that the possible benchmarking radiant power of 65.2 mW is achieved by the chemical substitution of Gd3+ and Sn4+. The presence of multiple excited behavior states (multiple luminescent centers) of Cr3+ due to its intermediate crystal field resulted in broadening of the emission spectrum along with increased intensity. The nonexponential decay character of the R-line and broadband luminescence further confirms the observation of the multiple excited state. The findings of this work are discussed based on structural characterization and spectroscopic studies at different measurement environments, and the potentials of the phosphors are also demonstrated by the prototype pc-NIR LED packaging