Uniform PMMA-CH₃NH₃PbBr₃ Nanoparticle Composite Film for Optoelectronic Application

Kirakosyan, Artavazd,Yun, Seokjin,Choi, Jihoon Materials Research Society of Korea 2017 한국재료학회지 Vol.27 No.6

Organometal halide perovskite materials, due to the tunability of their electronic and optical properties by control of composition and structure, have taken a position of significant importance in optoelectronic applications such as photovoltaic and lighting devices. Despite numerous studies on the structure - property relationship, however, practical application of these materials in electronic and optical devices is still limited by their processability during fabrication. Achieving nano-sized perovskite particles embedded in a polymer matrix with high loading density and outstanding photoluminescence performance is challenging. Here, we demonstrate that the careful control of nanoparticle formation and growth in the presence of poly(methyl methacrylate) results in perovskite nanoparticle - polymer nanocomposites with very good dispersion and photoluminescence. Furthermore, this approach is found to prevent further growth of perovskite nanoparticles, and thus results in a more uniform film, which enables fabrication using the perovskite nanoparticles.

Surface engineering for improved stability of CH₃NH₃PbBr₃ perovskite nanocrystals

Kirakosyan, Artavazd,Yun, Seokjin,Yoon, Soon-Gil,Choi, Jihoon The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.4

<P>Organohalide perovskite nanocrystals (NCs) with a variety of nano-scale structures and morphologies have shown promising potential owing to their size- and composition-dependent optoelectronic properties. Despite extensive studies on their size-dependent optical properties, a lack of understanding on their morphological transformation and the relevant stability issues limits a wide range of applications. Herein, we hypothesize a mechanism for the morphological transformation of perovskite NCs, which leads to dissolving NCs and forming microscale rectangular grains, resulting in a reduction of photoluminescence. We found that the morphological transformation from nanocrystal solids to microscale rectangular solids occurs <I>via</I> Ostwald ripening. A surface treatment with a surfactant suppresses the transformation, resulting in nearly monodisperse NCs with a square shape (∼20 nm edge size), and thus improves the stability of NC solution, as well as their photoluminescence performance and quantum yield (PLQY = 82%). Furthermore, we employed similar amine derivatives to investigate the effect of a molecular architecture (<I>i.e.</I> steric hindrance) on perovskite NC stability, which exhibited much enhanced PLQY (93%). These experimental results provide new insights into the fundamental relationship between the physical properties and the structure of perovskite nanocrystals required to understand their diverse optoelectronic properties.</P>

Self-Assembled Polymer-Grafted Nanoparticles for Photonic Coating Applications

Artavazd Kirakosyan,김들,최지훈 한국고분자학회 2016 Macromolecular Research Vol.24 No.11

Control of a regular arrangement of nanoparticles and their mechanical stability in a form of arrays and films becomes important in various particle-based technologies such as photonic bandgap materials. Here, we present that polymer-grafted nanoparticles (i.e. polystyrene-grafted silica nanospheres), synthesized by surface-initiated atom radical polymerization (SI-ATRP), can achieve ordered yet mechanically robust films by tuning the polymer brush architecture such as molecular weight and grafting density. Evolution of the particle arrangement in the polymer- grafted nanoparticle films is observed and associated with their wavelength at the maximum reflectance as well as their mechanical characteristics. This could open up new opportunities for fabrication of durable and highly ordered colloidal crystal structures such as photonic coating applications.

Formation of CH₃NH₃PbBr₃ Perovskite Nanocubes without Surfactant and Their Optical Properties

Artavazd Kirakosyan,Seokjin Yun,Deul Kim,Jihoon Choi 한국표면공학회 2018 한국표면공학회지 Vol.51 No.1

We systematically investigated the optical properties of sub-micron sized methylammonium lead tribromide (CH₃NH₃PbBr₃) cubes in the range of 100 to 700 nm, which were prepared by a surfactant-free precipitation method. We found that despite the strong absorbance, their photoluminescence quantum yield (PLQY) is very low as 0.009~0.011 % for whole range of sizes. Surfactant-free synthesis approach results in nanocubes that has no surface passivating reagents (e.g. surfactants) on their surface. As-prepared particles contain a large number of surface defects that may cause the low PLQY. The role of the surface defects were investigated in their photoluminescence decay process, which can be correlated with the particle size. Larger particles are characterized by a slower decay rate compared to smaller particles due to a large number of surface defects in the smaller particles that trap more excitons in the fluorescence decay process. These experimental results provide new insights into the fundamental relationship between surface state and optical properties.

Flexible h-BN foam sheets for multifunctional electronic packaging materials with ultrahigh thermostability

Kim, Deul,Kirakosyan, Artavazd,Lee, Jae Woong,Jeong, Jong-Ryul,Choi, Jihoon Royal Society of Chemistry 2018 SOFT MATTER Vol.14 No.20

<P>Recently developed electronic packaging materials based on low dimensional materials such as carbon nanotubes, graphene, and hexagonal boron nitride (h-BN) exhibit advantageous electrical, thermal, and mechanical properties for protecting electronic devices as well as dissipating heat flux from highly integrated circuits or high power electronic devices. Their thermal transport is mainly achieved by precise control of the nanostructure for nano-fillers to form the thermally conductive pathway. However, due to the viscoelastic behaviors of host polymeric materials, their phase or structural stability is significantly reduced by enhanced molecular motion at high temperature, resulting in poor thermal transport and mechanical strength. Here, we introduce flexible and robust h-BN foam sheets with a three-dimensional network structure, which exhibit much enhanced thermostability at high temperature. Furthermore, the additional infiltration of Fe3O4 nanoparticles into those structures results in relatively high electromagnetic absorbing performance. The combination of thermostability and mechanical strength based on the h-BN foam sheets provides novel opportunities for multifunctional thermally conductive materials in coatings and films without severely compromising auxiliary characteristics such as mechanical strength and thermal stability.</P>

Controlled morphology of MWCNTs driven by polymer-grafted nanoparticles for enhanced microwave absorption

Yun, Seokjin,Kirakosyan, Artavazd,Surabhi, Srivathsava,Jeong, Jong-Ryul,Choi, Jihoon The Royal Society of Chemistry 2017 Journal of materials chemistry. C, Materials for o Vol.5 No.33

<▼1><P>A simple and robust platform, based on polymer-grafted nanoparticles to facilitate a controlled morphology of nano-fillers, provides a route for strategically designing nanostructured EM wave absorbers with a percolated MWCNT network as well as a controlled NP arrangement.</P></▼1><▼2><P>The development of a lightweight electromagnetic (EM) wave absorber with a wider bandwidth and reflection loss at a low loading is of great interest for applications ranging from conventional electronic devices to specific devices or instruments of the military and aerospace. Although nano-filler (<I>i.e.</I> carbon nanotubes, magnetic nanoparticles, <I>etc.</I>) based polymer nanocomposites (PNCs) have shown great promise in this area of research, typically poor control of their surface modification and dispersion has prevented further development of these materials for application in EM wave absorbers. Here, we introduce and demonstrate a simple and robust platform based on polymer-grafted nanoparticles to facilitate a controlled morphology of nano-fillers, providing a route for strategically designing nanostructured EM wave absorbers with a percolated MWCNT network as well as a controlled NP arrangement. At equal loadings of nano-fillers (1 wt% of MWCNTs), much deeper reflection loss (RL = −26.9 dB at 5.4 GHz) and a wider bandwidth (4.9 GHz for RL < −10 dB) are observed compared to the conventional PNCs. We show that polymer-grafted nanoparticles serve as a matrix for unfunctionalized CNTs and show a much enhanced dispersion of CNTs, providing a novel opportunity for the multi-functional PNCs by combining functions arising from the controlled dispersion of heterogeneous materials (<I>i.e.</I> inorganic nanoparticles and CNTs) in a new type of CNT/NP/polymer nanostructure.</P></▼2>

Detection of volatile organic compounds (VOCs), aliphatic amines, using highly fluorescent organic-inorganic hybrid perovskite nanoparticles

Kim, Sung-Hoon,Kirakosyan, Artavazd,Choi, Jihoon,Kim, Jong H. Applied Science Publishers 2017 Dyes and pigments Vol.147 No.-

<P><B>Abstract</B></P> <P>In this work, a fluorescence chemosensor based on organic-inorganic hybrid CH<SUB>3</SUB>NH<SUB>3</SUB>PbBr<SUB>3</SUB> perovskite nanoparticles has been investigated for the detection of volatile organic compounds (VOCs), aliphatic amines (monoethylamine, diethylamine, and trimethylamine). Perovskite films showed fast (<1 s), highly discernible (89%), and reversible/irreversible fluorescence quenching behavior in response to the amine vapor exposure. Detection mechanism was confirmed by crystalline structural analysis based on X-ray diffraction (XRD) measurements and quantum chemical calculations, which proved that fluorescence quenching originates from the structural conversion from perovskite to its components by reversible or irreversible hydrogen bonding interaction between perovskite and aliphatic amines. This study suggests a simple but very effective strategy for naked eye-based fluorescence sensing of the colorless and harmful aliphatic amine vapors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Organometal halide perovskite nanoparticles are used as aliphatic amines vapor chemosensor. </LI> <LI> Fast (<1sec) and reversible/irreversible detection of aliphatic amines gas is demonstrated based on fluorescence quenching. </LI> <LI> Interaction of perovskite with polar aliphatic amines influencing fluorescence quenching are investigated. </LI> </UL> </P>

Electrostatic Stabilized InP Colloidal Quantum Dots with High Photoluminescence Efficiency

Mnoyan, Anush N.,Kirakosyan, Artavazd Gh.,Kim, Hyunki,Jang, Ho Seong,Jeon, Duk Young American Chemical Society 2015 Langmuir Vol.31 No.25

<P>Electrostatically stabilized InP quantum dots (QDs) showing a high luminescence yield of 16% without any long alkyl chain coordinating ligands on their surface are demonstrated. This is achieved by UV-etching the QDs in the presence of fluoric and sulfuric acids. Fluoric acid plays a critical role in selectively etching nonradiative sites during the ligand-exchange process and in relieving the acidity of the solution to prevent destruction of the QDs. Given that the InP QDs show high luminescence without any electrical barriers, such as long alkyl ligands or inorganic shells, this method can be applied for QD treatment for application to highly efficient QD-based optoelectronic devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2015/langd5.2015.31.issue-25/acs.langmuir.5b00847/production/images/medium/la-2015-00847v_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la5b00847'>ACS Electronic Supporting Info</A></P>

Tunable emission from blue to white light in single-phase Na(0.34)Ca(0.66-x-y)Al(1.66)Si(2.34)O8:xEu2+,yMn2+ (x = 0.07) phosphor for white-light UV LEDs.

Lee, Ga-yeon,Im, Won Bin,Kirakosyan, Artavazd,Cheong, Sang Hoon,Han, Ji Yeon,Jeon, Duk Young Optical Society of America 2013 Optics express Vol.21 No.3

<P>A series of single-phased emission-tunable Na(0.34)Ca(0.66)Al(1.66)Si(2.34)O(8):Eu(2+),Mn(2+) phosphors were successfully synthesized by a wet-chemical synthesis method. Photoluminescence excitation (PLE) spectra indicate that the phosphor can be efficiently excited by UV radiation from 250 to 420 nm. Also, NCASO:Eu(2+),Mn(2+) phosphor exhibit a broad blue emission band at 440 nm and an orange emission band at 570 nm, which originate from Eu(2+) and Mn(2+) ions, respectively. Therefore, overall emission color can be tuned from blue to white by increasing the concentration of Mn(2+) ions in the host lattice utilizing energy transfer from Eu(2+) to Mn(2+) ions. This energy transfer phenomenon was demonstrated to be a resonant type through dipole-dipole interaction determined with the help of PL spectra, decay time measurement, and energy transfer efficiency of the phosphor. These results indicate that NCASO:Eu(2+),Mn(2+) can be a promising single-phased white-emitting phosphor for white-light UV LEDs.</P>

Effect of Heat-treatment Temperature on the Formation of ε-Fe2O3 Nanoparticles Encapsulated by SiO2

Trinh Nguyen Thi,Phuoc Cao Van,Kirakosyan Artavazd,Chanyong Hwang,Jihoon Choi,Hyojin Kim,Jong-Ryul Jeong 한국자기학회 2023 Journal of Magnetics Vol.28 No.3

ε-Fe2O3 has received attention with particular interest because of its large coercive field at room temperature, high-frequency millimeter-wave absorption, and the coupling of its magnetic and dielectric properties. This work investigated the effect of heat treatment on the formation of ε-Fe2O3/SiO2 composites fabricated using reverse-micelle and sol-gel methods. The heating process was performed at various temperatures to figure out the optimal conditions for acquisition of the ε-Fe2O3 phase, which exhibits the largest coercive field among the Fe oxides. The sample treated at 1,075 °C had the highest percentage of ε-Fe2O3 phase, with a coercivity (HC) of 21.57 kOe measured at room temperature that reached a maximum of 23.7 kOe at 230 K. The measurement of the magnetization-temperature (M-T) curve for this sample also reveals the characteristic magnetic transition associated with ε-Fe2O3 within the temperature range of 40-150 K. The crystal structure of ε-Fe2O3 was confirmed using X-ray powder diffraction. Transmission electron micrographs revealed a broad size distribution of iron oxide nanoparticles ranging from 12 to 22 nm. The findings indicate that ε-Fe2O3 is a promising candidate with high electromagnetic-wave absorption capacity that is appropriate for high-speed wireless communication applications.