Optical properties of Eu(III) and Tb(III) complexes with pyridine- and quinoline- based ligands under high hydrostatic pressure

The spectroscopy of nitrate complexes of Eu(III) and Tb(III) with chiral and racemic imine-based [L1 = (N,N'-bis (2-pyridylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine) and L3 = N, N'-bis(2-quinolylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine] and amine-based [L2 = N,N'-bis(2-pyridylmethyl)-1,2-(R,R + S,S)-cyclohexanediamine) and L4 = N,N'-bis(2-quinolylmethyl)-1,2-(R,R + S,S)-cyclohexanediamine] ligands has been studied under high hydrostatic pressure (above 100 kbar). With the increasing pressure, a reduction of the Tb(III) and Eu(III) luminescence intensity is detected for all the complexes, whilst a significant reduction of the Tb(III) and Eu(III) excited state lifetimes has been observed for all Tb-based complexes [L1Tb(NO3)(3) -> L4Tb(NO3)(3)] and only for the Eu(III) complexes containing the imine-based ligands [L1Eu(NO3)(3) and L3Eu(NO3)(3)]. This behavior has been rationalized taking into account two main aspects: i) the relative position of the energy levels of the ligands and the metal ions and ii) the change of these position upon compression DFT calculations have been also performed to elucidate the nature of the orbitals involved in the UV electronic absorption transitions (NTO orbitals) upstream of the energy transfer process to the metal ion

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

Aluminate red phosphor in light-emitting diodes : theoretical calculations, charge varieties and high-pressure luminescence analysis

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). This research was also supported by National Centre for Re- search and Development, Poland (Grant No. PL- TW2/8/2015).Searching for a non-rare earth-based oxide red-emitting phosphor is crucial for phosphor-converted light- emitting diodes (LEDs). In this study, we optimized a blue and UV-light excited Sr4Al14O25:Mn phosphor exhibiting red emission peaked at ~653 nm, which was successfully synthesized by solid-state reaction. The crystal structure, micromorphology, and luminescent properties of Sr4Al14O25:Mn phosphors were characterized by X-ray Rietveld refinement, high-resolution transmission electron microscopy, and photoluminescence spectra. The band gap and electronic structure of Sr4Al14O25 were analyzed by density functional theory calculation using the hybrid exchange- correlation functional. The crystal field environment effect of Al sites from introducing activator Mn ions was investigated with the aid of Raman 27Al nuclear magnetic resonance spectra and electron spin resonance. The pressure dependent on the luminescent properties and decay time of this compound were presented. The tricolor display spectrum by combining blue InGaN chips, commercial β-SiAlON:Eu2+ green phosphor, and Sr4Al14O25:Mn red phosphor were evaluated for commercial applications: using the present Sr4Al14O25:Mn red phosphor converted LED as backlighting source.PostprintPeer reviewe

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 quenching in KYb(WO 4 ) 2 -Tb 3+ : An example of temperature-pressure equivalence

International audienceThe luminescence properties of a single crystal of KYb(WO4)2 doped with Tb3+ are investigated as a function of temperature at ambient pressure and at room temperature under high hydrostatic pressure. The observed quenching of the green Tb3+ (5D4→7F5) luminescence is ascribed to a pressure-induced downshift of the Tb3+→W6+ metal to metal charge transfer (impurity trapped exciton) state. A model is introduced to account for the pressure-induced quenching of the Tb3+ luminescence at room temperature in this double tungstate crystal