Browsing by Author "Lee, Szu-Ping"

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CaY2Si2S8:Ce3+: a novel green-emitting thiosilicate phosphor for white light-emitting diodes
(2014-11-14)
Lee, Szu-Ping
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Huang, Chien-Hao
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Chen, Teng-Ming
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應用化學系
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應用化學系分子科學碩博班
A novel green-emitting Ce3+-doped CaY2Si2S8 thiosilicate phosphor was synthesized by using solid-state methods in a sealed silica ampoule. This compound could be excited over a broad range from UV to blue light (400-450 nm) and generated a broadband emission peaking at similar to 495 nm, with a quantum efficiency of similar to 57%, which is promising for solid-state lighting applications. Temperature-dependent optical measurements of CaY2Si2S8:Ce3+ from 25 to 225 degrees C were performed. In addition, a white LED device was fabricated by using the green-emitting CaY2Si2S8:Ce3+ phosphor and commercially-available red-emitting CaAlSiN3:Eu2+ pumped with a 450 nm blue chip. The CRI value and CCT were measured to be 91-95 and 3800-8600 K, respectively, showing promising potential for solid-state lighting applications. The preparation, spectroscopic characterization, quantum efficiency, decay lifetime, thermal stability, and related LED device data are also presented.
New Ce3+-Activated Thiosilicate Phosphor for LED Lighting-Synthesis, Luminescence Studies, and Applications
(2014-05-28)
Lee, Szu-Ping
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Huang, Chien-Hao
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Chan, Ting-Shan
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Chen, Teng-Ming
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應用化學系
A new Ce3+-activated thiosilicate phosphor, BaLa2Si2S8:Ce3+, was synthesized by using solid-state methods in a fused silica ampule and found to crystallize in the structure type of La2PbSi2S8. The crystal structure has been characterized by synchrotron X-ray diffraction and refined with Rietveld methods. This novel cyan-emitting phosphor can be excited over a broad range from UV to blue light (380-450 nm) and generates a broadband emission peaking at 471 nm with a quantum efficiency of 36%. Nonradiative transitions between Ce3+ ions in BaLa2Si2S8:Ce3+ have also been demonstrated to be attributable to dipole-dipole interactions, and the critical distance was calculated to be 17.41 angstrom. When BaLa2Si2S8:Ce3+ phosphor was utilized to incorporate with yellow-emitting (Sr,Ca)(2)SiO4:Eu2+ phosphor and red-emitting CaAlSiN3:Eu2+ phosphor on a 430 nm blue LED chip, a warm white light LED device with color rendering index of similar to 96 was obtained. The results indicate that cyan-emitting BaLa2Si2S8:Ce3+ can serve as a potential phosphor for incorporation in fabrication of solid-state lighting. The preparation, spectroscopic characterization, quantum efficiency, decay lifetime, thermal-quenching behavior, and related LED device data are also presented.
Novel Eu2+-activated thiogallate phosphors for white LED applications: structural and spectroscopic analysis
(2018-01-01)
Lee, Szu-Ping
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Chan, Ting-Shan
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Dutta, Somrita
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Chen, Teng-Ming
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應用化學系
Novel Eu2+-activated BaGa2SiS6 and Ba2Ga8SiS16 thiogallate phosphors were prepared by solid-state reaction route. The BaGa2SiS6:Eu2+ phosphor generated a green emission upon excitation at 405 nm, whereas the Ba2Ga8SiS16:xEu(2+) phosphor could be tuned from cyan to green range with increasing Eu2+ concentration upon excitation at 365 nm. Additionally, the thermal luminescence properties of the thiogallate phosphors were investigated in the temperature range of 25 to 250 degrees C. A warm-white LED is fabricated using the combination of a 405 nm blue InGaN-based LED chip with the green-emitting BaGa2SiS6:0.01Eu(2+) phosphor, and red-emitting Sr2Si5N8:Eu2+ commercial phosphor with the CRI value of approximate to 88 and the CCT of 4213 K.
Novel Reddish-Orange-Emitting BaLa2Si2S8:Eu2+ Thiosilicate Phosphor for LED Lighting
(2015-01-14)
Lee, Szu-Ping
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Chan, Ting-Shan
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Chen, Teng-Ming
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應用化學系
;
應用化學系分子科學碩博班
A novel reddish-orange-emitting BaLa2Si2S8:Eu2+ thiosilicate was prepared in a sealed fused silica ampule and its crystal structure was refined using Rietveld methods. The BaLa2Si2S8:Eu2+ phosphor is excitable over a broad range from UV to blue (350-450 nm) and generated a reddish-orange broadband emission peaking at 645 nm with a quantum efficiency of similar to 24%. The thermal luminescence quenching of BaLa2Si2S8:Eu2+ was investigated over the range 25 to 150 degrees C. This phosphor was utilized to incorporate with two commercially available phosphors, blue BaMgAl10O17:Eu2+ and green (Ba,Sr)(2)SiO4:Eu2+, and a near-UV LED chip (405 nm), a white light with Ra of similar to 94 was obtained.
Sr3Ce(PO4)(3):Eu2+: a broadband yellow-emitting phosphor for near ultraviolet-pumped white light-emitting devices
(2016)
Dai, Pengpeng
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Lee, Szu-Ping
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Chan, Ting-Shan
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Huang, Chien-Hao
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Chiang, Yun-Wei
We have synthesized and investigated a series of yellow-emitting Sr3Ce(PO4)(3):Eu2+ phosphors, showing an extreme broadband at around 535 nm (with a FWHM of ca. 200 nm/6760 cm(-1)) and a large Stoke shift (ca. 8265 cm(-1)), which is attributed to the 4f-5d transition of Eu2+ without the contribution from Ce3+ emission under excitation at long wavelengths (> 370 nm). However, such broadband Eu2+ emission is rather surprising, considering that there is only one cation site for the Eu2+ luminescent center. Herein, we investigated the crystal structure by performing X-ray Rietveld refinement on the synchrotron X-ray diffraction data, and demonstrate that both cation and anion sites in Sr3Ce(PO4)(3) are disordered in the host lattice. These unusual structural characters generate a variety of distinct Eu2+ sites, which is verified by decay lifetime analysis and electron paramagnetic resonance spectra, and thus result in astonishing broadband yellow-emission. Moreover, a white LED device with a color-rendering index of 86.5, a color temperature of 5996 K, and chromaticity coordinates of (0.32, 0.38) was obtained by combining a 405 nm near-UV LED chip and the phosphor blends of yellow-emitting Sr3Ce(PO4)(3):Eu2+ and the commercial blue-emitting BaMgA(10)O(17):Eu2+ phosphor. These results indicate that the as-prepared yellow-emitting Sr3Ce(PO4)(3):Eu2+ phosphor has potential applications in the dual-color-phosphor-converted WLEDs.
Synthesis and Luminescence Properties of Novel Ce3+- and Eu2+-Doped Lanthanum Bromothiosilicate La3Br(SiS4)(2) Phosphors for White LEDs
(2016-04-13)
Lee, Szu-Ping
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Liu, Shuang-De
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Chan, Ting-Shan
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Chen, Teng-Ming
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應用化學系
Novel Ce3+- and Eu2+-doped lanthanum bromothiosilicate La3Br(SiS4)(2):Ce3+ and La3Br(SiS4)(2):Eu2+ phosphors were prepared by solid-state reaction in an evacuated and sealed quartz glass ampule. The La3Br(SiS4)(2):Ce3+ phosphor generates a cyan emission upon excitation at 375 nm, whereas the La3Br(SiS4)(2):Eu2+ phosphor could be excited with extremely broad range from UV to blue region (300 to 600 nm) and generates a reddish-orange broadband emission centered at 640 nm. In addition, thermal luminescence properties of La3Br(SiS4)(2):Ce3+ and La3Br(SiS4)(2):Eu2+ phosphors from 20 to 200 degrees C were investigated. The combination of a 450 nm blue InGaN-based LED chip with the red-emitting La3Br(SiS4)(2):Eu2+ phosphor, and green-emitting BOSE:Eu2+ commercial phosphor produced a warm-white light with the CRI value of similar to 95 and the CCT of 5,120 K. Overall, these results show that the prepared phosphors may have potential applications in pc-WLED.