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New emission band of PtOEP phosphor in organic LED devices
Taiju Tsuboi,Masayuki Tanigawa,Shin Kawami,Taishi Tsuji 한국물리학회 2005 Current Applied Physics Vol.5 No.1
Electroluminescence (EL) and transient EL response have been studied on organic light-emitting diode (OLED) devices based onphosphorescent PtOEP molecule. As the emitting layer, we used layer of PtOEP doped in CBP host material and layer formed by100%PtOEP (without doping in host). Three EL bands are observed at 500, 527 and 570 nm in the latter device besides red EL dueto PtOEP. The 500 and 527 nm ELs are attributed to emission from hole- and electron-transport layers, respectively, while the 570nm EL to emission from exciplex formed at the interface between the hole-blocking layer and emitting layer. Weak emission fromthe thermally populated triplet state is observed in single layer OLED device with 100%PtOEP layer and multi-layer device withPtOEP doped in host. Double exponential decay is observed in the electrophoresecence in the 100%PtOEP layer device, while asingle exponential decay is observed in the device with PtOEP doped in host.
Organic LED device based on PtOEP phosphor without dopingin host material
Taiju Tsuboi,Masayuki Tanigawa,Shin Kawami,Taishi Tsuji 한국물리학회 2005 Current Applied Physics Vol.5 No.6
Electroluminescence (EL) and photoluminescence (PL) have been studied on multi-layer organic light-emitting diode (OLED)devices based on phosphorescent platinum octaethyl porphine (PtOEP) molecule. A multi-layer OLED (called Pt5) which has100% PtOEP without doping in host as the emitting layer is investigated and compared its EL and PL characteristics with thoseof the other OLEDs (Pt2 and Pt3) with emitting layer of PtOEP doped in 4,40-N,N0-dicarbazole-biphenyl (CBP) host material. Itis observed that Pt5 shows a lower EL eciency than Pt2 and Pt3. Three broad EL bands are observed at 500, 527 and 570nmin the multi-layer device in addition to red sharp EL band due to PtOEP in Pt5, while only the red PtOEP EL is observed inPt2 and Pt3. The 500, 527 and 570nm EL peaks arise from absorption of the broad 525nm Alq3 emission band by PtOEP layer.The emission from the Alq3 electron-transport layer is caused by the carrier leakage from the hole-blocking BAlq layer. The inten-sity of red EL due to PtOEP is much weaker in Pt5 than in Pt2. Taking into account the result of PL, it is suggested that highlyecient energy transfer from CBP host to PtOEP guest occurs in Pt2 and Pt3, giving rise to higher PtOEP luminance, while con-centration quenching occurs in PtOEP layer in Pt5..
Du, Fuping,Nakai, Yosuke,Tsuboi, Taiju,Huang, Yanlin,Seo, Hyo Jin Royal Society of Chemistry 2011 Journal of materials chemistry Vol.21 No.12
<P>Eu<SUP>3+</SUP> doped red-emitting phosphors of double phosphates Ca<SUB>9</SUB>R(PO<SUB>4</SUB>)<SUB>7</SUB> (R = Al, Lu) were synthesized by a general high temperature solid-state reaction. The phosphors were characterized by X-ray powder diffraction (XRD). The detailed luminescence properties, <I>e.g.</I>, the emission spectra under the excitation of UV light, the photoluminescence excitation spectra and decay lifetimes were reported. The phosphors can be efficiently excited by near UV light to realize an intense red luminescence (613 nm) corresponding to the electric dipole transition <SUP>5</SUP>D<SUB>0</SUB> → <SUP>7</SUP>F<SUB>2</SUB> of Eu<SUP>3+</SUP> ions. The luminescence properties and the potential applications were analyzed. These phosphors were investigated by the site-selective emission spectra and the fluorescence decay curves in the <SUP>5</SUP>D<SUB>0</SUB> → <SUP>7</SUP>F<SUB>0</SUB> region using a pulsed, tunable, narrowband dye laser. It is suggested that Eu<SUP>3+</SUP> ions have three different crystallographic sites doped in Ca<SUB>9</SUB>Al(PO<SUB>4</SUB>)<SUB>7</SUB>, and five sites in Ca<SUB>9</SUB>Lu(PO<SUB>4</SUB>)<SUB>7</SUB> host. The site assignments of Eu<SUP>3+</SUP> ions in Ca<SUB>9</SUB><I>R</I>(PO<SUB>4</SUB>)<SUB>7</SUB> (<I>R</I> = Al, Lu) were discussed on the base of both optical spectroscopy results and structural analysis.</P> <P>Graphic Abstract</P><P>Eu<SUP>3+</SUP> ions occupy three and five kinds of crystallographic sites in Ca<SUB>9</SUB>Al(PO<SUB>4</SUB>)<SUB>7</SUB> and Ca<SUB>9</SUB>Lu(PO<SUB>4</SUB>)<SUB>7</SUB>, respectively. This was confirmed by the laser site-selective excitation and emission spectra of Eu<SUP>3+</SUP> ions. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0jm03324c'> </P>
Pu, Yinfu,Huang, Yanlin,Tsuboi, Taiju,Huang, Wei,Chen, Cuili,Seo, Hyo Jin Elsevier 2015 Materials letters Vol.149 No.-
<P><B>Abstract</B></P> <P>A self-activated yellow-emitting phosphor of nano-sized Cs<SUB>5</SUB>V<SUB>3</SUB>O<SUB>10</SUB> was synthesized by the Pechini method. The crystal phase and structure were investigated by X-ray diffraction (XRD) and structural refinement. The nanoparticles were characterized by scanning electron microscope (SEM) and X-ray photoelectron spectroscopic (XPS) measurements. Luminescence properties such as excitation and emission spectra as well as the absolute external quantum efficiency (<I>η</I>) are presented. Cs<SUB>5</SUB>V<SUB>3</SUB>O<SUB>10</SUB> is efficiently excited by UV light and X-ray and presents a bright yellow luminescence with the maximum <I>η</I> of 85.2%. It is suggested that Cs<SUB>5</SUB>V<SUB>3</SUB>O<SUB>10</SUB> is expected to be an efficient phosphor for lighting and display.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Efficient yellow-emitting Cs<SUB>5</SUB>V<SUB>3</SUB>O<SUB>10</SUB> nanoparticles were developed. </LI> <LI> Cs<SUB>5</SUB>V<SUB>3</SUB>O<SUB>10</SUB> has high quantum efficiency of 85.2% under UV light. </LI> <LI> Cs<SUB>5</SUB>V<SUB>3</SUB>O<SUB>10</SUB> shows scintillating luminescence with 40% intensity of that of Bi<SUB>4</SUB>Ge<SUB>3</SUB>O<SUB>12</SUB>. </LI> <LI> Efficient luminescence of Cs<SUB>5</SUB>V<SUB>3</SUB>O<SUB>10</SUB> is related to structural characteristics. </LI> </UL> </P>
Huang, Yanlin,Nakai, Yosuke,Tsuboi, Taiju,Seo, Hyo Jin Optical Society of America 2011 Optics express Vol.19 No.7
<P>The novel red-emitting phosphors of Eu<sup>3+</sup>-activated Ca<sub>2</sub>RF<sub>4</sub>PO<sub>4</sub>:Eu<sup>3+</sup> (R=Gd, Y) prepared by a solid-state reaction have been evaluated as a candidate for white solid state lighting. The detailed luminescence properties, e.g., the excitation spectra, the luminescence spectra and quantum efficiency under the excitation of near-UV, and decay lifetimes were reported. The phosphors can be efficiently excited by near UV light and exhibit a dominant emission peaked at 611 nm (<sup>5</sup>D<sub>0</sub>-<sup>7</sup>F<sub>2</sub>) with CIE coordinates of (x=0.661, y=0.333). The thermal stabilities were investigated from the luminescence intensities, color purity and the decay curves by increasing temperature. The luminescence parameters related to white LEDs applications were compared to some red phosphors and discussed in details. The red-emitting Ca<sub>2</sub>RF<sub>4</sub>PO<sub>4</sub>:Eu<sup>3+</sup> (R=Gd, Y) may be potentially useful in the fabrication of white LEDs.</P>
Spectroscopic ellipsometry study of Ir(ppy)3 organic light emitting diode
Nataliya Nabatova-Gabain,Yoko Wasai,Taiju Tsuboi 한국물리학회 2006 Current Applied Physics Vol.6 No.5
We studied the optical properties offactris(2-phenylpyridine) iridium (Ir(ppy)3) emitting layer in single-layer organic light emit-ting diode (OLED) device and in thin lm grown on quartz plate using a phase modulated spectroscopic ellipsometry (PMSE).Accurate spectra of refractive indexn and extinction coecientk of Ir(ppy)3 were obtained in the wavelength range of 330830 nm in the device and lm. Dierence was observed in then and k spectra between the single layer thin lm evaporated on quartzplate and OLED. Additionally dierence was found between the layer thickness estimated by quartz oscillator and thickness esti-mated from the PMSE measurement.
Novel yellow-emitting phosphors of Ca5M4(VO4)6 (M=Mg, Zn) with isolated VO4 tetrahedra.
Huang, Yanlin,Yu, Young Moon,Tsuboi, Taiju,Seo, Hyo Jin Optical Society of America 2012 Optics express Vol.20 No.4
<P>The self-activated yellow-emitting phosphors of vanadates Ca5M4(VO4)6 (M = Mg, Zn) were synthesized via the solid-state reaction route. The formation of single phase compound with garnet structure was verified through X-ray diffraction (XRD) studies. The excitation and emission spectra and the thermal quenching of luminescence intensities were measured. The different luminescence properties of Ca5Mg4(VO4)6 and Ca5Zn4(VO4)6 phosphors were presented, e.g., the spectra shift, the luminescence lifetimes, the absolute quantum efficiency, the color coordinates and the Stokes shift. This deference was discussed on the base of the relationship between the micro-structure and the charge transfer transitions in [VO4]3- groups in the lattices. Ca5Mg4(VO4)6 could be suggested to be a potential yellow-emitting phosphor for the application on near-UV excited white LEDs.</P>
서효진,김은식,장경혁,Liang Shi,Taiju Tsuboi,Kiyoshi Shimamura 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2
The luminescence properties of Er3+ ions doped in a calcium niobium gallium garnet (Ca3(NbGa)2-xGa3O12; CNGG) crystal are investigated by using laser excitation spectroscopy. The time-resolved emission spectra of Er3+ in CNGG are measured, together with the luminescence decays caused by the 355- and 532-nm pulsed laser excitations. Different emission spectra are observed at different time delays of 250 ns and 5 μs, which suggest that presence of Er3+ ions in different environments is responsible for the observed results.
Spectroscopic Properties of Er3+ Ions Doped in a Ca3(Nb2-x-zGaz)Ga3O12 Disordered Crystal
Eun Sik Kim,Hyo Jin Seo,장경혁,Liang Shi,Taiju Tsuboi,Kiyoshi Shimamura 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.2
Luminescence properties of Er³+ ions doped in a calcium niobium gallium garnet, Ca₃(Nb₂-x-z}Gaxz)Ga₃O12 (CNGG), disordered crystal are investigated by using optical absorption and emission spectroscopy. The energy levels of Er³+ in CNGG are identified by assignment of observed absorption and emission peaks in the spectral range of 300 -- 1600 nm. The broad emission band peaking at 470 nm and the broad excitation band peaking at 285 nm due to host sensitization are observed in both undoped and Er³+-doped CNGG crystals. The broad 470-nm emission band of Er³+-doped CNGG shows dips due to self-absorption by Er³+. The decays patterns of the ²H9/2, 4S3/2, 4F9/2 and 4I9/2 levels under excitation at 355 nm (corresponding to the ²G7/2 level) are revealed by multi-exponential decay curves which are due to decays of Er³+ in a crystal with disordered structure. The absorption and the emission spectra of the CNGG:Er³+ disordered crystal are compared with those of the YAlO₃:Er³+ ordered crystal. Luminescence properties of Er³+ ions doped in a calcium niobium gallium garnet, Ca₃(Nb₂-x-z}Gaxz)Ga₃O12 (CNGG), disordered crystal are investigated by using optical absorption and emission spectroscopy. The energy levels of Er³+ in CNGG are identified by assignment of observed absorption and emission peaks in the spectral range of 300 -- 1600 nm. The broad emission band peaking at 470 nm and the broad excitation band peaking at 285 nm due to host sensitization are observed in both undoped and Er³+-doped CNGG crystals. The broad 470-nm emission band of Er³+-doped CNGG shows dips due to self-absorption by Er³+. The decays patterns of the ²H9/2, 4S3/2, 4F9/2 and 4I9/2 levels under excitation at 355 nm (corresponding to the ²G7/2 level) are revealed by multi-exponential decay curves which are due to decays of Er³+ in a crystal with disordered structure. The absorption and the emission spectra of the CNGG:Er³+ disordered crystal are compared with those of the YAlO₃:Er³+ ordered crystal.