Ms. Tzu-Yi Lee Profile

Tzu-Yi Lee

at National Formosa Univ

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Publications (2)

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Proceedings Article | 15 September 2020 Presentation + Paper

High stability of perovskite CsPbBr3 quantum dots-based white light-emitting diodes

Tzu-Yi Lee, Shu-Ru Chung

Proceedings Volume 11464, 114640G (2020) https://doi.org/10.1117/12.2567888

KEYWORDS: Perovskite, Coating, Light emitting diodes, Silica, Time multiplexed optical shutter, Quantum dots, Electroluminescence, Transmission electron microscopy, Cesium

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At present, white light-emitting diodes (WLEDs) are widely used in display backlights. Commercialization of WLEDs are produced by using blue LED to excite phosphors, which with different colors resulting in a color gamut is only 75 % of the NTSC standard area due to a larger full width at half maximum (FWHM) of phosphors. Because of quantum dots (QDs) have narrow FWHM that can replace traditional phosphors as promising materials for white light backlights. Although inorganic perovskite CsPbBr3 green QDs have narrow FWHM, they are limited in WLED applications due to their low stability. In order to solve the above problem, silica coating is used to passivate the surface. The results show that the emission wavelength of CsPbBr3 QDs is redshifted due to agglomeration after coating with silica. After coating, the thermal stability of the sample has 24 % of improvement. The color gamut of WLEDs obtained by mixing green QDs with red phosphors (K2SiF6:Mn4+, KSF) are 131.5 % of NTSC for as-prepared sample and 124 % of NTSC for silica-coated sample. Compared above result with LAG-based WLED, the color gamut can be increased by 40 %. The WLED stability can be enhanced 12 times after coating. These results confirm that the color gamut of WLED obtained by mixing narrow bandwidth of KSF red phosphor and CsPbBr3 green QDs show a high NTSC to 131.5 %. As QD is coated with silica, the stability of QDs and WLED can be improved very significantly. This result is beneficial to the application of the CsPbBr3 green QD in the high color gamut display.

Proceedings Article | 21 August 2020 Poster + Presentation + Paper

High color rendering index of ZCIS quantum dots-based white light-emitting diodes

Wan-Xuan Lin, Yun-Xuan Huang, Tzu-Yi Lee, Pei-Ru Lin, Shu-Ru Chung

Proceedings Volume 11465, 1146513 (2020) https://doi.org/10.1117/12.2567896

KEYWORDS: Zinc, Solid state lighting, Light emitting diodes, Quantum dots, Optical properties, Copper, Absorption, Ultraviolet radiation, Transmission electron microscopy

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CuInS₂/ZnS quantum dots (CIS/ZnS QDs) have wide full width at half maximum (FWHM) due to the emission mechanism caused by point defect. This property make CIS/ZnS QD suitable for application in solid-state lighting (SSL). However, it was mentioned in the literature that white light-emitting diode (WLED) using CIS/ZnS QDs as the conversion material has low color rendering (CRI is less than 70), and one of the methods to increase the color rendering is increasing the range of the emission spectrum. CIS QDs belong to the point defects emission mechanism, and non-stoichiometric chemical substitution can create a large number of point defects. Therefore, in this study, CIS/ZnS QDs were first prepared by traditional thermal injection method, and (ZnCuIn)S₂ (ZCIS) QDs were prepared by adding Zn²⁺, Cu⁺ and In³⁺ ions at the same time. The results show that the emission wavelengths, relative quantum yield (QY), FWHM and surface morphology of CIS/ZnS QDs are 535 nm, 83 % and 72 nm and tetrahedron, respectively. On the other hand, those are 540 nm, 32 %, 118 nm and spherical shape for ZCIS QDs. Moreover, the diffraction peaks are between chalcopyrite and zinc blende structure meaning that the samples have alloyed structure. The CIE coordinates and color rendering index (CRI) of CIS/ZnS-based WLED are (0.35, 0.31) and 68. The CRI can be improved from 68 to 90 for ZCIS-based WLED. From the above results, it is known that ZCIS QDs with a FWHM up to 118 nm can be prepared by non-stoichiometric chemical substitution diffusion method. The wide FWHM shows positive effect to increase CRI value of ZCIS-based WLED and this advantage helps ZCIS QDs to be more widely used in solid-state lighting applications.

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