Browsing by Author "Verma, Akta"

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Fabrication of highly efficient hybrid device structure based white light emitting diodes
(2020-07-10)
Verma, Akta
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Sharma, S. K.
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Lin, Chih-Hao
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Manikandan, Arumugam
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Kuo, Hao-Chung
In this study, white light is generated from the combination of BaMgAl10O17:Mn2+ (BAM) green phosphor and colloidal red CdSe/ZnS quantum dots (QDs) via two different solid and hybrid type geometries. Problem of aggregation in solid type device is discussed in details and motivates us to move towards the fabrication of hybrid type device structure. The photoluminescence (PL) characterization was used to record the excitation and emission spectra of BAM and QDs materials. The size of CdSe/ZnS QDs was confirmed by transmission electron microscopy technique. The CdSe/ZnS QDs owned high quantum yield (>50%) and contributed to fabrication of high luminous efficiency of white light emitting diodes (WLEDs). The hybrid-type WLED showed 98% lm/W with outstanding color gamut values with a National Television System Committee (NTSC) value of 138% and Rec.2020 value of 105%. Moreover, the hybrid type device structure shows only 5% attenuation in luminous efficiency after 500 h of storage which maintains a great optical property.
Hybrid-type white LEDs based on inorganic halide perovskite QDs: candidates for wide color gamut display backlights
(2019-05-01)
Lin, Chih-Hao
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Verma, Akta
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Kang, Chieh-Yu
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Pai, Yung-Min
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Chen, Tzu-Yu
We demonstrate inorganic halide perovskite quantum-dots-based white light-emitting diodes via three different geometries, including liquid, solid, and hybrid types. Problems of fast anion exchange and aggregation in the cases of liquid- and solid-type devices are discussed in detail and push us to move towards the fabrication of a hybrid-type device structure. The experiment results illustrate that a hybrid-type device has the highest luminance efficiency (51 lm/W) and a wide color gamut (122% of NTSC and 91% of Rec. 2020). Therefore, we conclude that a hybrid-type device can provide an outstanding color gamut for high color gamut display applications. (c) 2019 Chinese Laser Press
Liquid Type Nontoxic Photoluminescent Nanomaterials for High Color Quality White-Light-Emitting Diode
(2018-12-22)
Lin, Chih-Hao
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Pai, Yung-Min
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Lee, Chun-Fu
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Verma, Akta
;
Lin, Huang-Yu
High-brightness white-light-emitting diodes (w-LEDs) with excellent color quality is demonstrated by using nontoxic nanomaterials. Previously, we have reported the high color quality w-LEDs with heavy-metal phosphor and quantum dots (QDs), which may cause environmental hazards. In the present work, liquid-type white LEDs composed of nontoxic materials, named as graphene and porous silicon quantum dots are fabricated with a high color rendering index (CRI) value gain up to 95. The liquid-typed device structure possesses minimized surface temperature and 25% higher value of luminous efficiency as compare to dispensing-typed structure. Further, the as-prepared device is environment friendly and attributed to low toxicity. The low toxicity and high R9 (87) component values were conjectured to produce new or improve current methods toward bioimaging application.
Ultrawide Color Gamut Perovskite and CdSe/ZnS Quantum-Dots-Based White Light-Emitting Diode with High Luminous Efficiency
(2019-09-01)
Lin, Chih-Hao
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Kang, Chieh-Yu
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Verma, Akta
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Wu, Tingzhu
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Pai, Yung-Min
We demonstrate excellent color quality of liquid-type white light-emitting diodes (WLEDs) using a combination of green light-emitting CsPbBr3 and red light-emitting CdSe/ZnS quantum dots (QDs). Previously, we reported red (CsPbBr1.2I1.8) and green (CsPbBr3) perovskite QDs (PQDs)-based WLEDs with high color gamut, which manifested fast anion exchange and stability issues. Herein, the replacement of red PQDs with CdSe/ZnS QDs has resolved the aforementioned problems effectively and improved both stability and efficiency. Further, the proposed liquid-type device possesses outstanding color gamut performance (132% of National Television System Committee and 99% of Rec. 2020). It also shows a high efficiency of 66 lm/W and an excellent long-term operation stability for over 1000 h.