Browsing by Author "Lee, Te-Ju"

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Charge-Transfer Luminescence and Energy Transfer in Eu(2+)-Doped Barium Zirconosilicates
(2011-01-01)
Wang, De-Yin
;
Wang, Ling-Li
;
Lee, Te-Ju
;
Chen, Teng-Ming
;
Cheng, Bing-Ming
Although zirconates are known to show ultraviolet luminescence under X-ray excitation, few have studied the vacuum ultraviolet (VUV) excited luminescence of zirconate compounds. We have investigated the VUV-excited luminescence of zirconate in BaZrSi(3)O(9) and Ba(2)Zr(2)Si(3)O(12) using synchrotron radiation, and examined the possibility of sensitizing Eu(2+) by hosts that contain zirconate. Upon VUV excitation, BaZrSi(3)O(9) and Ba(2)Zr(2)Si(3)O(12) show self-activated emission peaking at 285 nm and 334 nm, which are assigned to Zr(4+)-O(2-) charge transfer (CT) luminescence. The evidence for the occurrence of Zr(4+)-O(2-) charge transfer in BaZrSi(3)O(9) and Ba(2)Zr(2)Si(3)O(12) was further supported by density of state (DOS) calculation. Energy transfer from host excitation (similar to 172 nm) to Eu(2+) was observed in BaZrSi(3)O(9):Eu(2+) and Ba(2)Zr(2)Si(3)O(12):Eu(2+), showing that host sensitization of Eu(2+) occurs in these materials. Despite that the host emission overlaps with the Eu(2+) 4f-5d absorption band significantly, host -to-Eu(2+) energy transfer in Ba(2)Zr(2)Si(3)O(12):Eu(2+) was found to be less efficient than that in BaZrSi(3)O(9):Eu(2+) and Eu(2+) luminescence was found to be inferior in Ba(2)Zr(2)Si(3)O(12):Eu(2+). These observations are ascribed to a smaller Zr-O-Ba(Eu) angles and a lower Eu(2+)-Zr(4+) metal-to-metal charge transfer energy in Ba(2)Zr(2)Si(3)O(12):Eu(2+). (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.008112jes] All rights reserved.
Charge-Transfer Luminescence and Energy Transfer in Eu2+-Doped Barium Zirconosilicates
(2011-01-01)
Wang, De-Yin
;
Wang, Ling-Li
;
Lee, Te-Ju
;
Chen, Teng-Ming
;
Cheng, Bing-Ming
Although zirconates are known to show ultraviolet luminescence under X-ray excitation, few have studied the vacuum ultraviolet (VUV) excited luminescence of zirconate compounds. We have investigated the VUV-excited luminescence of zirconate in BaZrSi3O9 and Ba2Zr2Si3O12 using synchrotron radiation, and examined the possibility of sensitizing Eu2+ by hosts that contain zirconate. Upon VUV excitation, BaZrSi3O9 and Ba2Zr2Si3O12 show self-activated emission peaking at 285 nm and 334 nm, which are assigned to Zr4+-O2- charge transfer (CT) luminescence. The evidence for the occurrence of Zr4+-O2- charge transfer in BaZrSi3O9 and Ba2Zr2Si3O12 was further supported by density of state (DOS) calculation. Energy transfer from host excitation (similar to 172 nm) to Eu2+ was observed in BaZrSi3O9:Eu2+ and Ba2Zr2Si3O12:Eu2+, showing that host sensitization of Eu2+ occurs in these materials. Despite that the host emission overlaps with the Eu2+ 4f-5d absorption band significantly, host -to-Eu2+ energy transfer in Ba2Zr2Si3O12:Eu2+ was found to be less efficient than that in BaZrSi3O9:Eu2+ and Eu2+ luminescence was found to be inferior in Ba2Zr2Si3O12:Eu2+. These observations are ascribed to a smaller Zr-O-Ba(Eu) angles and a lower Eu2+-Zr4+ metal-to-metal charge transfer energy in Ba2Zr2Si3O12:Eu2+. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.008112jes] All rights reserved.
Eu(2+)-activated silicon-oxynitride Ca(3)Si(2)O(4)N(2): a green-emitting phosphor for white LEDs
(2011-05-09)
Chiu, Yi-Chen
;
Huang, Chien-Hao
;
Lee, Te-Ju
;
Liu, Wei-Ren
;
Yeh, Yao-Tsung
The green-emitting phosphor Ca(3)Si(2)O(4)N(2):Eu(2+) was synthesized using a solid-state reaction. The luminescence properties, diffuse reflection spectrum, and thermal quenching were firstly studied, and a white light-emitting diode (wLED) was fabricated using the Eu(2+)-activated Ca(3)Si(2)O(4)N(2) phosphor. Eu(2+)-doped Ca(3)Si(2)O(4)N(2) exhibited a broad green emission band centered between 510 and 550 nm depending on the concentration of Eu(2+). The optimal doping concentration of Eu(2+) in Ca(3)Si(2)O(4)N(2) was 1 mol%. The energy transfer between Eu(2+) ions proceeds by an electric multipolar interaction mechanism, with a critical transfer distance of approximately 30.08 angstrom. A wLED with an color-rendering index R(a) of 88.25 at a correlated color temperature of 6029 K was obtained by combining a GaN-based n-UV LED (380 nm) with the blue-emitting BaMgAl(10)O(17):Eu(2+), green-emitting Ca(3)Si(2)O(4)N(2): Eu(2+), and red-emitting CaAlSiN(3):Eu(2+) phosphors. The results present Ca(3)Si(2)O(4)N(2):Eu(2+) as an attractive candidate for use as a conversion phosphor for wLED applications. (C) 2011 Optical Society of America
Eu2+-activated silicon-oxynitride Ca3Si2O4N2: a green-emitting phosphor for white LEDs
(2011-05-09)
Chiu, Yi-Chen
;
Huang, Chien-Hao
;
Lee, Te-Ju
;
Liu, Wei-Ren
;
Yeh, Yao-Tsung
The green-emitting phosphor Ca3Si2O4N2:Eu2+ was synthesized using a solid-state reaction. The luminescence properties, diffuse reflection spectrum, and thermal quenching were firstly studied, and a white light-emitting diode (wLED) was fabricated using the Eu2+-activated Ca3Si2O4N2 phosphor. Eu2+-doped Ca3Si2O4N2 exhibited a broad green emission band centered between 510 and 550 nm depending on the concentration of Eu2+. The optimal doping concentration of Eu2+ in Ca3Si2O4N2 was 1 mol%. The energy transfer between Eu2+ ions proceeds by an electric multipolar interaction mechanism, with a critical transfer distance of approximately 30.08 angstrom. A wLED with an color-rendering index R-a of 88.25 at a correlated color temperature of 6029 K was obtained by combining a GaN-based n-UV LED (380 nm) with the blue-emitting BaMgAl10O17:Eu2+, green-emitting Ca3Si2O4N2: Eu2+, and red-emitting CaAlSiN3:Eu2+ phosphors. The results present Ca3Si2O4N2:Eu2+ as an attractive candidate for use as a conversion phosphor for wLED applications. (C) 2011 Optical Society of America
Investigation of Pr(3+) as a sensitizer in quantum-cutting fluoride phosphors
(2008-02-25)
Lee, Te-Ju
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Luo, Li-Yang
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Cheng, Bing-Ming
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Diau, Wei-Guang
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Chen, Teng-Ming
A quantum-cutting (QC) phosphor K(2)GdF(5):Eu(3+) shows poor optical absorption and a theoretical quantum efficiency (QE) of 107% in the ultraviolet (UV) and vacuum ultraviolet (VUV) excitation spectral ranges. Pr(3+) was codoped as a sensitizer in K(2)GdF(5): Eu(3+) thus increasing the absorption in the UV and VUV spectral regions; the theoretical QE of K(2)GdF(5): Eu(3+), Pr(3+) was increased to 138%. The spectra indicate that the possible mechanisms of QC and energy transfer differ from those of phosphors containing the Gd(3+) -Eu(3+) couple. Temporally resolved measurements of fluorescence decay confirm the proposed QC mechanism for the phosphor containing the Gd(3+) -Eu(3+),Pr(3+) system. (C) 2008 American Institute of Physics.
Regiocontrolled Synthesis of Ethene-Bridged para-Phenylene Oligomers Based on Pt(II)- and Ru(II)-Catalyzed Aromatization
(2010-01-01)
Chen, Tse-An
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Lee, Te-Ju
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Lin, Ming-Yuan
;
Sohel, Shariar M. A.
;
Dian, Eric Wei-Guang
We report the regiocontrolled syntheses of ethene-bridged para-phenylene oligomers in three distinct classes by using Pt(II)- and Ru(II)-catalyzed aromatization. This synthetic approach has been developed based on twofold aromatization of the 1-aryl-2-alkynyl-benzene functionality, which proceeds by distinct regioselectivity for platinum and ruthenium catalysts. Variable-temperature NMR spectra provide evidence that large arrays of these oligomers are prone to twist from planarity. The UV/Vis and photoluminescence (PL) spectra as well as the band gaps of these regularly growing arrays show a pattern of extensive pi conjugation with increasing array sizes, except for in one instance.
Regiocontrolled Synthesis of Ethene-Bridged para-Phenylene Oligomers Based on Pt-II- and Ru-II-Catalyzed Aromatization
(2010-01-01)
Chen, Tse-An
;
Lee, Te-Ju
;
Lin, Ming-Yuan
;
Sohel, Shariar M. A.
;
Dian, Eric Wei-Guang
We report the regiocontrolled syntheses of ethene-bridged para-phenylene oligomers in three distinct classes by using Pt-II- and Ru-II-catalyzed aromatization. This synthetic approach has been developed based on twofold aromatization of the 1-aryl-2-alkynyl-benzene functionality, which proceeds by distinct regioselectivity for platinum and ruthenium catalysts. Variable-temperature NMR spectra provide evidence that large arrays of these oligomers are prone to twist from planarity. The UV/Vis and photoluminescence (PL) spectra as well as the band gaps of these regularly growing arrays show a pattern of extensive pi conjugation with increasing array sizes, except for in one instance.
Visible quantum cutting through downconversion in green-emitting K2GdF5 : Tb3+ phosphors
(2006-09-25)
Lee, Te-Ju
;
Luo, Li-Yang
;
Diau, Eric Wei-Guang
;
Chen, Teng-Ming
;
Cheng, Bing-Ming
Visible quantum cutting under excitations at 212 and 172 nm in a green-emitting phosphor K2GdF5:Tb3+ (11%) via a downconversion mechanism is investigated. The authors measured the vacuum ultraviolet (VUV) excitation and emission spectra and proposed mechanisms to rationalize the quantum-cutting effect. One short-UV or one VUV photon absorbed by Tb3+ is split into multiple visible photons emitted by Tb3+ through cross relaxation and direct energy transfer. Calculations indicate an optimal quantum efficiency as great as 189% for this phosphor. (c) 2006 American Institute of Physics.