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Effect of Reaction Time on Optical Properties of CsPbBr₃ Perovskite Nanocrystals
Sung Hun Kim,Yong-Ryun Jo,Yong Bin Kim,Ju Seok Kim,Sang-Youp Yim,Hong Seok Lee 한국진공학회(ASCT) 2021 Applied Science and Convergence Technology Vol.30 No.5
We have studied the optical and structural properties of CsPbBr₃ perovskite nanocrystals (NCs) fabricated with various reaction times. The temporal evolution of the ensemble optical properties, such as absorption and fluorescence (FL) spectra and photoluminescence quantum yield (PLQY), was recorded under a set reaction temperature (170 ℃) and various amounts of time (5 s – 60 min). The FL intensity of the CsPbBr₃ NCs gradually decreased with increasing reaction time, and the observed PLQY of the CsPbBr₃ NCs ranged from less than 20% up to 35% because of the enlarged crystal size and the induced charge trap states. The FL peaks of as-obtained CsPbBr₃ NCs were tuned in the range of 516.8 to 526.8 nm with increasing reaction time as a result of the ripening phenomenon. Transmission electron microscopy and selected area electron diffraction analysis were performed to analyze the structural properties. The results revealed that the average edge length of CsPbBr₃ NCs with a reaction time of 5 s was 13.4 nm and confirmed that the cubic crystal structure was well ordered.
Hong, Sang-Hyun,Cho, Chu-Young,Lee, Sang-Jun,Yim, Sang-Youp,Lim, Wantae,Kim, Sung-Tae,Park, Seong-Ju Optical Society of America 2013 Optics express Vol.21 No.3
<P>We demonstrate localized surface plasmon (LSP)-enhanced near-ultraviolet light-emitting diodes (NUV-LEDs) using silver (Ag) and platinum (Pt) nanoparticles (NPs). The optical output power of NUV-LEDs with metal NPs is higher by 20.1% for NUV-LEDs with Ag NPs and 57.9% for NUV-LEDs with Pt NPs at 20 mA than that of NUV-LEDs without metal NPs. The time-resolved photoluminescence (TR-PL) spectra shows that the decay times of NUV-LEDs with Ag and Pt NPs are faster than that of NUV-LEDs without metal NPs. The TR-PL and absorbance spectra of metal NPs indicate that the spontaneous emission rate is increased by resonance coupling between excitons in the multiple quantum wells and LSPs in the metal NPs. (C) 2013 Optical Society of America</P>
Jin, Sung Hwan,Kim, Su Hwan,Yim, Sang-Youp,Choi, Jin Chul,Lee, Hong Seok Elsevier 2017 Materials research bulletin Vol.96 No.3
<P><B>Abstract</B></P> <P>We studied the optical properties of multilayer CdTe/ZnTe quantum dots (QDs) with various ZnTe separation layer thicknesses on GaAs substrates. The low temperature photoluminescence (PL) spectra show that the excitonic peaks in multilayer CdTe/ZnTe QDs shift to higher energy levels, and PL peak intensities increase with increasing ZnTe separation layer thickness. This is because of increasing uncoupling and because there are many more carriers confined in the QDs with wider separation layers. Temperature-dependent PL measurements showed that the activation energies of the confined electrons in the multilayer CdTe/ZnTe QDs decreases with decreasing ZnTe separation layer thickness. The time-resolved PL spectra show increasing carrier decay times with decreasing ZnTe separation layer thickness, due to increasing coupling between QDs with narrower separation layers.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kim, Na-Yeong,Leem, Young-Chul,Hong, Sang-Hyun,Park, Jin-Ho,Yim, Sang-Youp American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.6
<P>We demonstrated the effects of monolayer graphene and hexagonal boron nitride (h-BN) on the stability and detection performance of two types of substrates in surface-enhanced Raman scattering (SERS): a two-dimensional (2D) monolayer/Ag nanoparticle (NP) substrate and a Au NP/2D monolayer/Ag NP substrate. Graphene and h-BN, which have different electrical and chemical properties, were introduced in close contact with the metal NPs and had distinctly different effects on the plasmonic near-field interactions between metal NPs in the subnanometer-scale gap and on the electron transport behavior. A quantitative comparison was possible due to reproducible SERS signals across the entire substrates prepared by simple and inexpensive fabrication methods. The hybrid platform, an insulating h-BN monolayer covering the Ag NP substrate, ensured the long-term oxidative stability for over 80 days, which was superior to the stability achieved using conducting graphene. Additionally, a sandwich structure using an h-BN monolayer exhibited excellent SERS sensitivity with a detection limit for rhodamine 6G as low as 10<SUP>-12</SUP> M; to the best of our knowledge, this is the best SERS detection limit achieved using monolayer h-BN as a gap-control material. In this study, we suggest an efficient strategy for hybridizing the desired 2D layers with metal nanostructures for SERS applications, where the substrate stability and electromagnetic field enhancement are particularly crucial for the various applications that utilize metal/2D hybrid structures.</P> [FIG OMISSION]</BR>
Lee, Kyu Seung,Shim, Jaeho,Lee, Hyunbok,Yim, Sang-Youp,Angadi, Basavaraj,Lim, Byungkwon,Son, Dong Ick The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.29
<P>Hybrid organic-Red-Green-Blue (RGB) color quantum dots were incorporated into consolidated p(polymer)-i(RGB quantum dots)-n(small molecules) junction structures to fabricate a single active layer for a light emitting diode device for white electroluminescence. The semiconductor RGB quantum dots, as an intrinsic material, were electrostatically bonded between functional groups of the p-type polymer organic material core surface and the n-type small molecular organic material shell surface. The ZnCdSe/ZnS and CdSe/ZnS quantum dots distributed uniformly and isotropically surrounding the polymer core which in turn was surrounded by small molecular organic materials. In the present study, we have identified the mechanisms of chemical synthesis and interactions of the p-i-n junction nanocell structure through modeling studies by DFT calculations. We have also investigated optical, structural and electrical properties along with the carrier transport mechanism of the light emitting diodes which have a single active layer of consolidated p-i-n junction nanocells for white electroluminescence.</P>
Lee, Da Hoon,Park, Jung Su,Hwang, Jong Ho,Kang, Dooho,Yim, Sang-Youp,Kim, Joon Heon Royal Society of Chemistry 2018 Journal of Materials Chemistry C Vol.6 No.23
<P>Recently, nanoporous gold nanoparticles have attracted great interest due to their optical and catalytic properties. However, most reports on their fabrication are based on the dealloying method. Here, we report a new fabrication technique for hollow nanoporous gold nanoshells (NPGNSs) with high structural tunability by sintering chemically synthesized gold nanoparticles (AuNPs) on the surface of polymer colloid particles. Size reduction of the colloid template by plasma etching induces contact of the AuNPs on the colloid surface. Elimination of the capping layers of AuNPs by plasma etching facilitates sintering of the contacted AuNPs. Complete removal of the colloid template after AuNP sintering results in hollow NPGNSs. A combination of AuNPs and polymer colloid templates of different sizes can change the structure and optical properties of hollow NPGNSs. Furthermore, AuNPs of different shapes, such as gold nanorods with a high aspect ratio and spherical AuNPs, can be used to make hollow NPGNSs, which gives more flexibility in tuning their structures. Our proposed fabrication technique based on shrinkage of templates and sintering of nanoparticles can be a new platform to prepare hollow nanoporous metal structures having nanoscale overall sizes with high structural tunability.</P>
Choi, Hojoong,Seo, Sehun,Lee, Jong-Hoon,Hong, Sang-Hyun,Song, Jaesun,Kim, Seungkyu,Yim, Sang-Youp,Lee, Kwanghee,Park, Seong-Ju,Lee, Sanghan Royal Society of Chemistry 2018 Journal of Materials Chemistry C Vol.6 No.22
<P>UV phototransistors based on ZnO, a material considered promising owing to its wide direct bandgap and high stability in harsh environments, have been intensively investigated. However, ZnO singlelayer UV phototransistors, especially solution-processed devices, still exhibit poor electrical and UV photoresponse characteristics. Herein, we report the fabrication of a low-cost, large-area, and highperformance solution-processed ZnO/SnO2 bilayer UV phototransistor with improved electrical and UV photoresponse characteristics attained by inserting a SnO2 carrier transport layer, which is the actual path of the electrons. The photogenerated electrons are readily transferred from the ZnO UV-sensitive layer to the SnO2 carrier transport layer, owing to the lower conduction band of the SnO2 carrier transport layer than the ZnO UV-sensitive layer. In addition, the efficient extraction of photogenerated electrons from the ZnO UV-sensitive layer through the SnO2 carrier transport layer with high field effect mobility contributes to the improvement in the UV photoresponse characteristics of the ZnO/SnO2 bilayer UV phototransistor. The ZnO/SnO2 bilayer UV phototransistor exhibits high responsivity and detectivity as well as fast photoresponse. These results demonstrate that the solution-processed ZnO/SnO2 bilayer UV phototransistor developed in this study provides a novel approach for improving the performance of UV phototransistors with low-cost and large-area processing.</P>