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Luminescent Properties and Energy Transfer of Green-Emitting Ca3Y2(Si3O9)(2):Ce3+,Tb3+ Phosphor
(2009-01-01)
Chiu, Yi-Chen
;
Liu, Wei-Ren
;
Yeh, Yao-Tsung
;
Jang, Shyue-Ming
;
Chen, Teng-Ming
Green-emitting phosphors of Ca3Y2(Si3O9)(2):Ce3+,Tb3+ have been synthesized by solid-state reaction. The luminescence properties were characterized by photoluminescence (PL) and photoluminescence excitation spectra, reflection spectra, and a detection system using an integrating sphere equipped with a spectrofluorometer. With Ce3+ co-doping as a sensitizer, the PL intensity of Ca3Y2(Si3O9)(2):Ce3+,Tb3+ was found to increase dramatically by a factor of 5.8. For comparison, the emission intensity of composition-optimized Ca3Y2(Si3O9)(2):Ce3+,Tb3+ is 126% of green commodity, ZnS:Cu,Al. The quantum efficiency of Ca3Y2(Si3O9)(2):Ce3+,Tb3+ is as high as 77% compared to ZnS:Cu,Al (53%). The energy transfer from Ce3+ to Tb3+ is also of resonant type via a dipole-dipole mechanism with the energy-transfer critical distance of 6.78 A degrees. By utilizing the principle of energy transfer and appropriate tuning of activator contents, we are currently evaluating the potential application of Ca3Y2(Si3O9)(2):Ce3+,Tb3+ as a highly efficient UV-convertible phosphor.
Intense blue-emitting Ca2PO4Cl:Eu2+ phosphor for near-ultraviolet converting white light-emitting diodes
(2010-12-01)
Chiu, Yi-Chen
;
Liu, Wei-Ren
;
Chang, Chun-Kuei
;
Liao, Cheng-Chun
;
Yeh, Yao-Tsung
A blue phosphor Ca2PO4Cl:Eu2+ (CAP:Eu2+) was synthesized by solid state reaction. The Ca2PO4Cl:Eu2+ exhibited high quantum efficiency and excellent thermal stability. The luminescent intensity of Ca2PO4Cl:Eu2+ was found to be 128% under excitation at 380 nm, 149% under 400 nm, and 247% under 420 nm as high as that of BaMgAl10O17:Eu2+. The optimal doping concentration was observed to 11 mol.% of CAP:Eu2+. The energy transfer between Eu2+ ions in CAP were occurred via electric multipolar interaction, and the critical transfer distance was estimated to be 1.26 nm. A mixture of blue-emitting Ca2PO4Cl:Eu2+, green-emitting (Ba,Sr)(2)SiO4:Eu2+ and red-emitting CaAlSiN3:Eu2+ phosphors were selected in conjunction with 400 nm chip to fabricate white LED devices. The average color-rendering index R-a and correlated color temperature (T-c) of the white LEDs were found to be 93.4 and 4590 K, respectively. The results indicated that it was a promising candidate as a blue-emitting phosphor for the near-UV white light-emitting diodes.
Assessment of Luminescent Downshifting Layers for the Improvement of Light-Harvesting Efficiency in Dye-Sensitized Solar Cells
(2014-12-01)
Hosseini, Zahra
;
Diau, Eric Wei-Guang
;
Mehrany, Khashayar
;
Taghavinia, Nima
;
應用化學系
Luminescence downshifting (LDS) of light can be a practical photon management technique to compensate the narrow absorption band of high-extinction-coefficient dyes in dye-sensitized solar cells (DSSCs). Herein, an optical analysis on the loss mechanisms in a reflective LDS (R-LDS)/DSSC configuration is reported. For squaraine dye (550-700 nm absorption band) and CaAlSiN3:Eu2+ LDS material (550-700 nm emission band), the major loss channels are found to be non-unity luminescence quantum efficiency (QE) and electrolyte absorption. By using an ideal LDS layer (QE=100%), a less absorbing electrolyte (Co-based), and antireflection coatings, approximately 20% better light harvesting is obtained. If the absorption/emission band of dye/LDS is shifted to 800 nm, a maximal short-circuit current density (J(sc)) of 22.1 mAcm(-2) can be achieved. By putting the LDS layer in front of the DSSC (transmissive mode), more significant loss channels are observed, and hence a lower overall efficiency than the R-LDS configuration.
The effect of In2O3 conductive coating on the luminescence and zeta potential of ZnS : Cu, Al phosphors
(2005)
Chang, CH
;
Chiou, BS
;
Chen, KS
;
Ho, CC
;
Ho, JC
Phosphors used in CRTs have been coated with In2O3 conductive layer derived from the hydrolysis of indium chloride. It was found that brightness of the phosphors rises initially with the amount of InCl3, reaches a maximum at 10 Wt-% InCl3 and then decreases when more InCl3 was added. With 10 wt.% InCl3 coating, the brightness of ZnS:Cu, Al phosphor increases by 24% at 800 V and I RA while very little changes were observed in the luminescent emission peak and CIE color loci. The luminescence decay times increase with the increase of the conductive coating. However, they are shorter than 0.7 mu s for samples with the amount of coating ranging from 0 to 20 wt.% InCl3 and are Suitable for display applications. Conductive coating affects the surface chemistry of the phosphor particles, enhances the zeta potential of ZnS:Cu, Al in IPA solution. and, consequently, increases the electrophoretic deposition rate of the phosphors onto substrate. The zeta potential of 10 wt.% InCl3 coated ZnS:Cu, Al in isopropyl alcohol solution is 32 mV as compared to 1.2 mV of that of the uncoated ZnS:Cu, Al. Besides, the electrophoretic deposition rate of the 10 wt.% InCl3 coated ZnS:Cu, Al (0.23 mg/s) is larger than that of the uncoated phosphor (0.17 mg/s). (c) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Enhanced Light Harvesting with a Reflective Luminescent Down-Shifting Layer for Dye-Sensitized Solar Cells
(2013-06-26)
Hosseini, Zahra
;
Huang, Wei-Kai
;
Tsai, Cheng-Ming
;
Chen, Teng-Ming
;
Taghavinia, Nima
For a dye-sensitized solar cell with a near-infrared squaraine (SQ1) sensitizer, the photovoltaic performance was enhanced remarkably with a reflective luminescent down-shifting (R-LDS) layer to increase the light-harvesting efficiency at the wavelength region 400-550 nm where the SQ1 dye has weak absorption. Relative enhancements greater than 200% in IPCE near 500 nm and 40-54% in J(SC) were achieved with red phosphor CaAlSiN3:Eu2+ as the LDS material, attaining 5.0 and 4.8% overall efficiencies of power conversion for the R-LDS layer coated on the counter electrode (front illumination) and working electrode (back illumination), respectively.
Vacuum ultraviolet spectral investigations on green-emitting Ca (La, Gd)(4) Si3O13 : Tb3+ phosphors for PDP applications
(2006-12-01)
Wu Chia-Chin
;
Cheng Bing-Ming
;
Chen Teng-Ming
;
應用化學系
;
Department of Applied Chemistry
In an effort to develop new green-emitting PDP phosphors with high efficiency, investigated were the synthesis, VUV photoluminescence (PL) spectra, optical properties, and chromaticity of Ca(La1-x-yTbxGdy)(4)Si3O13 phosphors by using synchrotron radiation. Upon analysis of the VUV spectroscopic and chromaticity investigations on the new green-emitting VUV phosphors, were an optimized composition achieved. The PLE spectral studies show that Ca(La1-x-y TbxGdy)(4)Si3O13 exhibit significant absorption in the VUV range. The VUV PL intensity was found to enhance with Gd3+ - doping. Furthermore, the 1931 CIE chromaticity coordinates of Ca(La,Gd)(4)Si3O13:Tb were found to be (0.286, 0.548), as compared to (0.230, 0.712) for Zn2SiO4:Mn2+ as a reference. The potential application of Ca(La,Gd)(4)Si3O13:Tb as a new green-emitting PDP phosphor are being currently improving and evaluating.
Structural, spectroscopic and photolurninescence studies of LiEu(WO4)(2-x)(MoO4), as a near-UV convertible phosphor
(2007-02-01)
Chiu, Chuang-Hung
;
Wang, Ming-Fang
;
Lee, Chi-Shen
;
Chen, Teng-Ming
;
應用化學系
A series of lithium europium double tungsto-molybdate phosphors LiEu(WO4)(2-),(MoO4), (X = 0, 0.4, 0.8, 1.2, 1.6, 2.0) have been synthesized by solid-state reactions and their crystal structure, optical and luminescent properties were studied. As the molybdate content increases, the intensity of the D-5(0) -> F-7(2) emission of Eu3+ activated at wavelength of 396 mn was found to increase and reach a maximum when the relative ratio of Mo/W is 2:0. These changes were found to be accompanied with the changes in the spectral feature, which can be attributed to the crystal field splitting of the D-5(0) -> F-7(2) transition. As the molybdate content increases the emission intensity of the 615 nm peak also increases. The intense red-emission of the tungstomolybdate phosphors under near-UV excitation suggests them to be potential candidate for white light generation by using near-UV LEDs. In this study the effect of chemical compositions and crystal structure on the photolumineseent properties of LiEu(WO4)(2-x)(MoO4), is investigated and discussed. (c) 2006 Elsevier Inc. All rights reserved.
Synthesis, composition optimization, and VUV photoluminescence characterization of (Y,Gd) (V,P) O-4 : Eu3+ as a potential red-emitting plasma-display panel phosphor
(2007-12-01)
Wu, Chia-Chin
;
Cheng, Bing-Ming
;
Chen, Teng-Ming
;
應用化學系
;
Department of Applied Chemistry
The synthesis, composition optimization, VUV Photoluminescence (PL) spectra, and optical properties, of (Y, Gd) (V, P)O-4 : Eu3+ phosphors were investigated by synchrotron radiation. The VUV PLE spectra and the correlation among VUV PL intensity, lambda(em), and Eu3+, Gd3+, and P-content were established. The PLE spectral studies showed that (Y, Gd) (V, P)O-4: Eu3+ exhibited significant absorption in the VUV range. The VUV PL intensity was found to enhance with PO43- and Gd3+ -doping. Furthermore, the chromaticity characteristics of (Y, Gd) (V, P)O-4: Eu3+ were also found to be (0.6614, 0.3286) and compared against (Y, Gd)BO3:Eu3+ as a reference. Based on the characterization results, we are currently improving and evaluating the potential application of (Y, Gd) (V, P)O-4: Eu3+ as a new red-emitting PDP phosphor.
A lighting mechanism for flat electron emission lamp
(2009-03-02)
Li, Jung-Yu
;
Chen, Shih-Pu
;
Li, Chia-Hung
;
Lin, Yi-Ping
;
Chou, Yen-I
We propose a lighting mechanism for generating uniform planar light. The device integrates electron beams induced by gas discharge with cathodoluminescence at the anode, where the spectra of the emitted light depend entirely on the phosphor materials coated on the anode. Consequently, ultraviolet is not required and the usage of mercury can be avoided. In addition, the features of double-side lighting, transparency, and gray-scale images indicate that the flat electron emission lamp might become potential candidate for the next generation green lighting source.
Visible quantum cutting in green-emitting BaGdF5 : Tb3+ phosphors via downconversion
(2007-01-01)
Tzeng, Hsin-Yi
;
Cheng, Bing-Ming
;
Chen, Teng-Ming
;
應用化學系
;
Department of Applied Chemistry
The visible quantum cutting (QC) under the excitation at 215 and 187nm in a newly discovered BaGdF5:Tb3+ via downconversion mechanism has been observed and investigated. We have measured the vacuum ultraviolet (VUV) excitation and emission spectra and proposed possible mechanisms to rationalize the observed QC effect. In QC process, one short-wavelength UV or one VUV photon absorbed by Tb3+ was found to split into more than one visible photon emitted by Tb3+ through cross-relaxation and subsequent direct energy transfer between Tb3+ and Tb3+ and/or Gd3+ ions, depending on the excitation wavelength. On the basis of the calculations from the emission spectra in the visible region obtained, we have obtained optimal quantum efficiency as high as 168% and 180% for green-emitting BaGdF5:Tb3+ under excitation at 215 and 187 nm, respectively. (c) 2006 Elsevier B.V. All rights reserved.

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