Search

Technological progress has accelerated the researches into broadband near‐infrared (NIR) luminescent materials as next‐generation intelligent NIR light sources; however, poor thermal stability restricts the applications of NIR phosphors. Herein, new insights into Cr3+‐activated NIR phosphors with improved thermal stability are provided. The photoluminescence intensity originating from the 4T2→4A2 broadband emission of CaLu2Al4SiO12:Cr3+ (CLAS:Cr) with optimal electron occupation (4T2/2E) increases up to 118% at 475 K compared with that at room temperature, which is the best for Cr3+‐activated broadband NIR phosphor. Accordingly, new ideas for the design of thermally stable phosphors are proposed by optimizing the thermal population between 4T2 and 2E states and electron migration from 2E to 4T2 state. Finally, multifunctional applications of CLAS:Cr in NIR fluorescence intensity ratio thermometry, X‐ray detection, NIR phosphor‐converted light‐emitting diodes, and bio‐imaging are demonstrated. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C 3 N 4) has shown promising potentials for quantum dot light-emitting diodes (QLEDs), which might be an effective alternative of the mostly used Cd(Se,S)/Zn(S,Se) emitting layers and can achieve both low toxicity and high stability, meeting the goal of sustainable development. Herein, we for the first report a white electroluminescent QLED device with blue and orange dual-color emissions, which were attributed to the σ*-LP, π*- π, and π*-LP transitions, respectively, from a single-compound g-C 3 N 4 quantum dots (QDs) by synthesizing the precursor at 0.8 Mpa high-pressure N 2. By selectively exciting the δ and π bonds with X-ray, the luminescence mechanism was approved with the synchrotron radiation techniques of X-ray absorption near edge structure (XANES) and the X-ray excited optical luminescence (XEOL).The chromaticity coordinate changes from cayan color space with CIE (0.2034, 0.1939) to white color space with CIE (0.3009, 0.2697) as pressure increases from 0.06 to 0.8 Mpa, with the increased overlap of the δ* and π* orbital upon the contraction of crystal lattice. The breakthrough achieved in this work will promisingly promote the development of future white light sources as thin as paper for human home and office lighting by using direct current-driven electroluminescence of QDs, instead of photoluminescence of phosphors. [Display omitted] [ABSTRACT FROM AUTHOR]

Exploration of novel red emitting phosphors containing Eu3+ ions is an everlasting topic in the field of luminescent materials due to the application requirement of warm white light-emitting diodes. In this work, the Eu3+-doped ScCaO(BO 3) phosphors were synthesized though the high temperature solid-state reaction method. The phase purity and detail information on crystal structure were obtained by X-ray diffraction (XRD) and the technology of Rietveld XRD refinement. Scanning electron microscopy (SEM) was applied to check the particle morphology and EDS mapping was taken to analyze element distributions. Optical properties of the phosphors were studied by measuring the steady-state excitation and emission spectra and also the transient luminescence decays. The emission spectra of ScCaO(BO 3):Eu3+ majorly consisted of 5D 0 -7F 1 , 7F 2 and 7F 4 transitions, covering the orange (582–605 nm), red (605–635 nm) and deep red (690–720 nm) spectral regions. The doping concentration of Eu3+ ions was optimized to 12% to maximize the optical performance of the red emitting phosphors, whose CIE coordinate and fluorescent lifetime were (0.6458, 0.3537) and 1.516 ms, respectively. The investigation of the thermal quenching behavior of the ScCaO(BO 3):0.12Eu3+ phosphor reveals that the emission intensity of Eu3+ at 400 K can maintain 68.98% of that at room temperature due to the existence of the thermal activation energy of 0.258 eV. Using such a red-emitting material, the prototype warm white LED device with the CIE coordinate of (0.3262, 0.3363), color rendering index of 86.1 and correlated color temperature of 5871 K can be obtained by combining with the blue emitting BaMgAl 10 O 17 :Eu2+ and green emitting Zn 2 SiO 4 :Mn2+ phosphors and coating all three on a near-UV LED chip. All the results demonstrate that the ScCaO(BO 3):0.12Eu3+ phosphor can sever as a potential red emitting candidate for near-UV excited warm WLEDs. • A novel red phosphor ScCaO(BO 3):Eu3+ has been synthesized. • The quantum efficiency of ScCaO(BO 3):0.12Eu3+ phosphor can reach 73.51%. • The obtained phosphors are suitable for tricolor-composited white light. [ABSTRACT FROM AUTHOR]

The green-emitting phosphor SrSi 2 O 2 N 2 : Eu2+, along with the cyan-emitting phosphor BaSi 2 O 2 N 2 : Eu2+, is a key component for phosphors used to package natural sunlight full-spectrum LED devices. Thereby, the synthesis of high-efficiency and thermal-stability luminous SrSi 2 O 2 N 2 : Eu2+ with an economic approach is very important for the development of LED industry. In this work, the syntheses of SrSi 2 O 2 N 2 : Eu2+ phosphors were optimized from four aspects: strontium sources, reaction atmospheres, reaction vessels, and reaction fluxes. Meanwhile, the relationship among photoluminescence performances, crystal structures, and morphologies were examined. The results show that the synthesis of SrSi 2 O 2 N 2 : Eu2+ from SrO and Sr(NO 3) 2 sources are beneficial to obtain N-rich oxynitide structure, which is helpful to improve luminescence. By employing SrCO 3 and Sr(NO 3) 2 as strontium sources, however, the SrSi 2 O 2 N 2 : Eu2+ is O-rich and the by-product Sr 2 Si 5 N 8 :Eu is introduced. The optimal conditions for the synthesis of SrSi 2 O 2 N 2 : Eu2+ is by utilizing SrO as a strontium source, in N 2 atmosphere, adopting Mo crucible, and adding NH 4 Cl as flux. The quantum yield of the optimal SrSi 2 O 2 N 2 : Eu2+ phosphor under the excitation of 380 nm reaches up to 100%. Image 1 • In addition to carbonate and orthosilicate routes, this work reports a third one to synthesize SrSi 2 O 2 N 2 :Eu2+. • Among variant strontium sources, SrO was approved as the best for synthesis of SrSi 2 O 2 N 2 :Eu2+. • The N-rich oxynitride is helpful to improve luminescence efficiency of SrSi 2 O 2 N 2 :Eu2+. • Reaction of SrO with Si 3 N 4 in N 2 atmosphere with NH 4 Cl as flux is optimal synthesis for SrSi 2 O 2 N 2 :Eu2+. • The quantum yield of SrSi 2 O 2 N 2 :Eu2+ excited with 380 nm reaches up to 100%. [ABSTRACT FROM AUTHOR]