Search

A spiro‐axis skeleton not only introduces circularly polarized luminescence (CPL) into thermally activated delayed fluorescence (TADF) molecules but also enhances the intramolecular through space charge transfer (TSCT) process. Spiral distributed phenoxazine and 2‐(trifluoromethyl)‐9H‐thioxanthen‐9‐one‐10,10‐dioxide act as donor and acceptor units, respectively. The resulting TADF enantiomers, (rac)‐OSFSO, display emission maxima at 470 nm, small singlet‐triplet energy gap (ΔEST) of 0.022 eV and high photoluminescence quantum yield (PLQY) of 81.2 % in co‐doped film. The circularly polarized OLEDs (CP‐OLEDs) based on (R)‐OSFSO and (S)‐OSFSO display obvious circularly polarized electroluminescence (CPEL) signals with dissymmetry factor up to 3.0×10−3 and maximum external quantum efficiency (EQEmax) of 20.0 %. Moreover, the devices show remarkably low efficiency roll‐off with an EQE of 19.3 % at 1000 cd m−2 (roll‐off ca. 3.5 %), which are among the top results of CP‐OLEDs. [ABSTRACT FROM AUTHOR]

Sr2Si5N8:Eu2+ nitride phosphors application for light emitting diodes were synthesized for the first time using less-expensive and air-stable entire oxides raw materials, Sr CO3, SiO2, and Eu2O3, through a carbothermal reduction and nitridation (CTRN) route. The reaction dynamic processes of the CTRN route and the phase components, photoluminescent properties, quantum efficiency as well as thermal stability for the resultant Sr2Si5N8:Eu2+ phosphors were investigated in detail. High-crystalline pure Sr2Si5N8:Eu2+ red-emitting phosphor with acceptant luminescent performances could be obtained through finely controlling addition amount of carbon reductant agent and carefully removing the residual carbon without oxidation damage. An economic route is outlined in this work for the synthesis of nitride phosphors using cost-effective entire oxides raw materials, thereby driving the development and practical application of nitrides phosphors. [ABSTRACT FROM AUTHOR]

A remote phosphor coating by using Sr(Al,Si)(O, F):Ce (SASF:Ce) on glass substrate was prepared by a simple and convenient screen printing method. The crystalline phase and the distribution of SASF:Ce crystals in coating were investigated by XRD and SEM, respectively. The scattering light and absorption light properties of remote phosphor coating with different thicknesses were discussed through Lambert-Beer's law. The relationship between luminous efficiency and absorption coefficient was demonstrated. White light emitting diode prototype fabricated with blue chip and the prepared patterned SASF:Ce remote phosphor in this work showed excellent performances, opening a cost-effective process to generate planar white light. [ABSTRACT FROM AUTHOR]

Tricolor emission CaSiO:Ln (Ln = Ce, Eu, Sm) phosphors were synthesized by the conventional solid-state reaction method, and their photoluminescence properties were investigated. Ce-, Eu-, or Sm-doped CaSiO phosphors showed typical blue, green, or red luminescence in the CIE1931 chromaticity diagram, respectively. In addition, the luminescence efficiency of the tricolor emission CaSiO:Ln (Ln = Ce, Eu, Sm) phosphors was evaluated. A series of white light-emitting diode (LED) prototypes were fabricated by combining near-UV LED chip and the as-prepared tricolor emission phosphors with various ratios in weight. White LED prototypes with tunable correlated color temperature and color-rendering index values were realized by controlling the amount of phosphors. The presented results indicated the potential application of CaSiO:Ln (Ln = Ce, Eu, Sm) phosphors in near-UV white LED. [ABSTRACT FROM AUTHOR]

Abstract: Tricolor emission in a same Ca3Si2O7 host with independent Ln (LnCe3+, Eu2+, Tb3+) dopants is demonstrated to construct a near-UV white light emitting diode (LED). The luminescence properties and thermal quenching properties, as well as the applications in near-UV white LED are investigated. These phosphors show typical blue, red, and green, three-basal-color, luminescence in the CIE chromaticity diagram for Ce3+, Eu2+ and Tb3+ dopants, respectively. Thermal quenching properties show that the luminescence thermal stability strongly depends on the different dopant types; better thermal quenching property of Ce3+ and Tb3+ is recorded in comparison with that of Eu2+. The white LED prototype fabricated with near-UV chip and as-prepared tricolor phosphors exhibits acceptable CIE chromaticity coordinates (0.32, 0.30) with a CCT of 6000K and a CRI of 87, indicating the potential application of Ca3Si2O7:Ln phosphors in near-UV white LED. [Copyright &y& Elsevier]

The role of Si in the valence state of Ce and phase control in YAG:Ce phosphors was investigated upon incorporation of Si-O in the form of SiO. By varying the amount of SiO addition, the valence state of tetravalent and trivalent Ce ions was identified distinctly by X-ray photoelectron spectroscopy and the phase purity of YAG host phase was examined by X-ray diffraction patterns. The self-reduction phenomena from Ce to Ce in YAG:Ce samples was observed to be featured in a typical 5d → 4f yellow-green transition of Ce ion upon firing in air, driven by charge compensation for imbalance substitution of Ce for Y. The addition of SiO promotes further reduction of Ce to Ce in an amount up to 7.0 wt%, owing to spontaneous charge compensation, and suppresses the formation of YAP (yttrium aluminate perovskite, YAlO) and YAM (yttrium aluminate monoclinic, YAlO). The results reveal the role of SiO addition in a proper amount to be able to achieve desired luminous center of Ce and phase-pure YAG for a series of YAG hosted luminescence materials such as blue-excitable YAG phosphor or laser-pumped YAG-based transparent ceramics or glass ceramics for lighting and display purposes. [ABSTRACT FROM AUTHOR]

Abstract: By adding Si3N4 to the Eu-, Mn-doped Ba3MgSi2O8 upon firing, the formation of a new phase, Ba2SiO4, and its resultant variation of luminescent properties are investigated to compensate the green-light-emission for full-color. Upon addition of Si3N4, a ∼507-nm peaked band emission of Eu in Ba2SiO4 was induced in coexistence with the concurrent blue-, and red-light-emissions of Eu and Mn in Ba3MgSi2O8. Amount of each phase and as such the transfer of energy in between can be tuned by varying the amount of Si3N4 added, resulting in an interactive change of intensity in between Eu for blue-, green-band-transitions and Mn for red-band-transition in two different phases, due to the indirect contribution of Si3N4 to the formation of Ba2SiO4 and red-shift of photoluminescence. Consequently, white-light with CIE chromaticity coordinate (0.2605, 0.3084) at an optimized amount of Si3N4 has been achieved with this nitride-added adjustable strategy. [Copyright &y& Elsevier]

Abstract: White light emission (Sr0.85Mg0.14)3(P1−x Si x O4)2: Dy3+ phosphors applied for white light emitting diodes (LEDs) were synthesized by the solid state reaction process. The phases and luminescence properties of the obtained (Sr0.85Mg0.14)3(P1−x Si x O4)2: Dy3+ phosphors were well characterized. The presented results demonstrate that the (Sr0.85Mg0.14)3(P1−x Si x O4)2: Dy3+ particles emit an intensive white light emission under excitation at 350nm. Additionally, the effect of Si4+ incorporation concentration on the luminescence properties of (Sr0.85Mg0.14)3(PO4)2: Dy3+ was investigated in detail. [Copyright &y& Elsevier]

Abstract: Novel Eu2+ doped SiAlON-crystal/glass composite white-light-emitting phosphor applied in ultraviolet (UV) based white light-emitting-diode (LED) was prepared by a facile strategy instead of traditional recrystallization procedure. Blue-emitting glass phase was introduced in yellow-emitting α-SiAlON:Eu2+ micron-crystal phosphor by simple heat-treatment with the addition of nano-SiO2 or B2O3. As a result, white-light emission with CIE chromaticity coordinates (0.31, 0.33) and (0.32, 0.37) was demonstrated by mixing blue and yellow light for B2O3 and SiO2 induced crystal/glass composite phosphor, respectively. This variety of white-light-emitting phosphors in such a crystal/glass composite structure shows potential applications in UV white LED to be free of complicated multicomponent phosphor blending operation. [Copyright &y& Elsevier]

We report a plant growth lamp utilizing near-ultraviolet light-emitting diode and A3MgSi2O8:Eu2+, Mn2+ (A=Ca,Sr,Ba) phosphors with emission spectra consisting of blue and red bands, which conform well to the action spectra of plants and absorption spectra of chlorophylls. Either peak positions of the two bands or intensity ratio of red to blue band can be tailored by tuning the compositions of the cations. Eu–Mn energy transfer in the phosphors was investigated on the bases of photoluminescence, life decay time, and microstructure. This functional solid-state lighting provides a simple, compact, and efficient solution to illuminator for plant cultivation. [ABSTRACT FROM AUTHOR]

Abstract: Novel single-phased white-light-emitting Ca2.96(P0.99B0.01O4)2:0.04Dy3+ phosphors for light-emitting diode (LED) applications were synthesized by conventional solid-state reactions. The phases and luminescent properties of the obtained Ca2.96(P0.99B0.01O4)2:0.04Dy3+ phosphors were well characterized. The results show that the excited bands of Ca2.96(P0.99B0.01O4)2:0.04Dy3+ phosphor centered at wavelengths of 324nm (6H15/2→4M17/2), 350nm (6H15/2→4M15/2, 6P7/2), 366nm (6H15/2→4I11/2), 387nm (6H15/2→4I13/2, 4F7/2), 427nm (6H15/2→4G11/2), and 448nm (6H15/2→4I15/2). On excitation at 350nm, the emission transitions of Dy3+ consisted of double emission bands, which can be assigned to the transition emissions of 4F9/2→6H15/2 (480nm) and 4F9/2→6H13/2 (572nm). One mol% B3+ dopant improved the luminescence intensity of Ca2.96(PO4)2:0.04Dy3+ phosphor, and the reason was proposed. The developed phosphor has great potential as a single-component white-light-emitting phosphor for UV-light-emitting diodes. [Copyright &y& Elsevier]

Ca 19(1- x) M 2 (PO 4) 14 :19 x Eu3+ (M = Mg, Zn) (x = 0.05, 0.07, 0.09, 0.10, 0.11 and 0.12) red phosphors were successfully synthesized by the high-temperature solid-phase reaction method. The phase composition, morphology and characteristic photoluminescence properties of Ca 19 Mg 2 (PO 4) 14 (CMPO):Eu3+ and Ca 19 Zn 2 (PO 4) 14 (CZPO):Eu3+ were analyzed by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM) and photoluminescence spectroscopy. The photoluminescence excitation (PLE) and emission (PL) spectra of both samples indicate that the phosphors can be effectively excited by ultraviolet (UV) and blue light, and also it is shown that the electric-dipole transition of Eu3+ is dominant. The typical concentration quenching occurs when Eu3+-doping concentrations of both phosphors exceed 10 mol%, and the PL intensity of CZPO:0.10Eu3+ sample is 1.65 times that of CMPO:0.10Eu3+. Furthermore, the infrared spectra (IR), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) curves, ultraviolet–visible diffuse reflectance spectra (UV–Vis DRS), thermal stability, chromaticity coordinates (CIE) and correlated color temperature (CCT) of Ca 19 M 2 (PO 4) 14 :Eu3+ phosphors were evaluated in detail. The band gaps of CMPO and CZPO hosts were equal to 6.46 and 6.39 eV, respectively. The I 423K / I 298K values of CMPO:Eu3+ and CZPO:Eu3+ phosphors are as high as 73.89% and 88.29%. The chromaticity coordinates of Ca 19(1- x) M 2 (PO 4) 14 :19 x Eu3+ (M = Mg, Zn) phosphors locate in red region, and the color purity values of CMPO:Eu3+ and CZPO:Eu3+ are determined to be 99.82% and 99.61%, respectively. To sum up, the phosphors are considered as the potential luminescence materials for use in white light emitting diodes (w-LEDs). • Ca 19 Mg 2 (PO 4) 14 :Eu3+ and Ca 19 Zn 2 (PO 4) 14 :Eu3+ red emitting phosphors were prepared. • The PL intensity of CZPO:0.10Eu3+ sample is 1.65 times that of CMPO:0.10Eu3+. • The thermal stability of CMPO:Eu3+ and CZPO:Eu3+ are as high as 73.89% and 88.29%. • The color purity of CMPO:Eu3+ and CZPO:Eu3+ are determined to be 99.82% and 99.61%. [ABSTRACT FROM AUTHOR]

The novel red-emitting Ca 9 MY 0.667 (PO 4) 7 (M = Li, Na) (CMYPO): x Eu3+ (x = 0.02, 0.04, 0.07, 0.12, 0.16, 0.26, 0.35, and 0.44) phosphors were successfully synthesized by a high-temperature solid-phase reaction. The samples were evaluated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared (FT-IR) spectra, ultraviolet–visible diffuse reflectance (UV–Vis DR) spectra, photoluminescence excitation (PLE) and emission (PL) spectra. It is found that the samples can be excited by near-ultraviolet (NUV) and blue light. The intense PL peaks were centered at 614 nm due to the 5D 0 → 7F 2 transition. Interestingly, 5D 0 → 7F 4 (700 nm) far-red emission matches with the far-red absorption wavelength required for plant photosensitive pigments red (P R) and far-red (P FR) light. Moreover, the PL intensity of Ca 9 NaY 0·667 (PO 4) 7 (CNYPO):Eu3+ is higher than that of Ca 9 LiY 0·667 (PO 4) 7 (CLYPO):Eu3+. In addition, the band gaps of CLYPO and CNYPO were determined to be 3.81 and 3.61 eV, respectively. Finally, the International Commission on Illumination (CIE) chromaticity of phosphors are located in red region. The results showed that the phosphors are considered as the potential luminescence materials in white light emitting diodes (w-LEDs). Impressively, the as-prepared samples can provide reference for the development of Eu3+-doped phosphors that can be used for plant growth LEDs. Image 1 • 5D 0.→ 7F 4 emission matches the far-red absorption required for P R and P FR. • The PL intensity of CNYPO:Eu3+ is higher than that of CLYPO:Eu3+. • The Eu3+-doped phosphors can be used for plant growth LEDs. [ABSTRACT FROM AUTHOR]

A new red luminescent material Ca 9 LiBi 2/3 (PO 4) 7 :Eu3+ (CLBPO:Eu3+) was synthesized by high temperature solid state reaction, and characterized by X-ray powder diffraction (XRD), field emission scanning electric microscopy (FESEM) and fluorescence spectroscopy. The XRD patterns indicated that CLBPO:Eu3+ phosphor has been successfully synthesized. The photoluminescence excitation (PLE) spectra and emission (PL) spectra of phosphor, as well as the relationship between PL intensity and concentration were discussed. The results exhibit that the PL peak of CLBPO:Eu3+ phosphor is mainly centered at 616 nm under 395 nm excitation, which is attributed to 5D 0 →7F 2 transition of Eu3+ ions. In addition, the 5D 0 → 7F 4 transition around 700 nm belongs to the far-red emission, which matches well with the far-red absorption wavelength required for plant photosensitive pigments P FR. Moreover, when the doping concentration of Eu3+ is 80 mol%, the PL intensity of phosphor reaches the maximum. The calculated International Commission on Illumination (CIE) coordinates lie in the red region and the color purity of CLBPO:0.8Eu3+ is determined to be 99.76%. The correlated color temperature (CCT) value of CLBPO:Eu3+ is less than 3500 K, belonging to warm red light. In view of the aforementioned interesting luminescent properties, the prepared phosphor possesses high application potential in the fabrication of phosphor-converted white light emitting diodes (WLED), and plant growth lighting. • The Ca 9 LiBi 0.667 (PO 4) 7 :Eu3+ sample was synthesized by high temperature method. • The distinctive far-red light emission due to the 5D 0.→7F 4 can match well with P FR. • The color purity of CLBPO:0.8Eu3+ is determined to be 99.76%. • The CCT value of CLBPO:Eu3+ is less than 3500 K, belonging to warm red light. • The CLBPO:Eu3+ can be applied to plant growth lighting. [ABSTRACT FROM AUTHOR]

A series of Ca 2 La 8 (SiO 4) 6 O 2 :Eu3+ (CLSO:Eu3+) and Ca 4 La 6 (SiO 4) 4 (PO 4) 2 O 2 :Eu3+ (CLSPO:Eu3+) oxyapatite phosphors have been prepared via traditional solid-state reaction process. The phase composition of phosphors was analyzed by X-ray powder diffraction (XRD), and the morphology was evaluated by scanning electron microscopy (SEM). The characteristic photoluminescence properties were evaluated by analysis of photoluminescence excitation (PLE) and emission (PL) spectra. In addition, the luminescence decay times and emission-temperature relationship were also characterized. The results indicated that the phosphors could be efficiently excited by the near ultraviolet (NUV) light and blue light, and they exhibited red light emission. Meanwhile, the average particle sizes of CLSO and CLSPO hosts are about 2∼8 μm. Moreover, the low symmetry C 3 or C s sites appropriate for Eu3+ in the CLSO and CLSPO hosts are benefit to 5D 0 → 7F 2 electric dipole transition, which leads to greater R/O values of CLSO: y Eu3+ than those of CLSPO: y Eu3+. All the obtained results suggested that the prepared phosphors have a potential for application in white light emitting diodes (WLEDs). • Novel CLSO:Eu3+/CLSPO:Eu3+ red phosphors have been successfully synthesized. • The optimal concentration of Eu3+ are 40 mol% (CLSO) and 60 mol% (CLSPO). • The E a of CLSO:0.4Eu3+ and CLSPO:0.6Eu3+ are 0.230 and 0.303 eV, respectively. • The PL intensity of CLSO:0.4Eu3+ is 1.29 times than that of CLSPO:0.6Eu3+. [ABSTRACT FROM AUTHOR]