Visible and near-infrared upconversion in α-sialon ceramics

Kshetri, Yuwaraj K.,Joshi, Bhupendra,Kim, Tae-Ho,Lee, Soo W. Royal Society of Chemistry 2017 Journal of Materials Chemistry C Vol.5 No.14

<▼1><▼1><P>Intense near-infrared to visible and near-infrared upconversion emissions are realized in Er<SUP>3+</SUP>/Ho<SUP>3+</SUP>/Tm<SUP>3+</SUP> doped α-sialon ceramics.</P></▼1><▼2><P>α-Sialon ceramics are well known for highly stressed structural engineering applications owing to their inherently outstanding mechanical and thermo-chemical stability. However, the possibilities of the functional applications such as frequency upconversion in α-sialon ceramics have been scarcely investigated. Here, very intense visible and near-infrared frequency upconversion as well as frequency downconversion emissions are reported for the first time in Er<SUP>3+</SUP>, Ho<SUP>3+</SUP>, and Tm<SUP>3+</SUP> triply doped α-sialon ceramics under 980 nm excitation. α-Sialon ceramics are prepared using a hot press sintering technique. Efficient energy transfer processes between the dopant ions are found to be responsible for the observed emissions. The upconversion process is governed by a two-photon absorption process. The energy transfer efficiency in the triply doped system is 95.8% while that in Er<SUP>3+</SUP>/Ho<SUP>3+</SUP> and Er<SUP>3+</SUP>/Tm<SUP>3+</SUP> systems is 71.6% and 66.3%, respectively. Triple doping results in the combination of the emission properties found in the co-doped Er<SUP>3+</SUP>/Ho<SUP>3+</SUP> and Er<SUP>3+</SUP>/Tm<SUP>3+</SUP> systems and it also reveals a cooperative emission behavior which is not possible with only two dopants. These findings open up the possibility of potential application of the Er<SUP>3+</SUP>/Ho<SUP>3+</SUP>/Tm<SUP>3+</SUP> doped α-sialon ceramic as an optical material in which efficient luminescent properties can co-exist along with the excellent mechanical and thermo-chemical stability.</P></▼2></▼1>

Efficient near infrared to visible and near‐infrared upconversion emissions in transparent (tm3+, er3+)‐α‐sialon ceramics

Kshetri, Yuwaraj K.,Joshi, Bhupendra,Diaz‐,Torres, Luis Armando,Lee, Soo Wohn American Ceramic Society 2017 Journal of the American Ceramic Society Vol. No.

Blue, green, red and near-infrared emissions via upconversion in α-sialon

Kshetri, Yuwaraj K.,Joshi, Bhupendra,Kim, Tae-Ho,Lee, Soo Wohn Elsevier 2017 Materials letters Vol.199 No.-

<P>Near-infrared to visible and near-infrared upconversion emission has been reported in Yb3+/Ln(3+) (Ln(3+) = Er3+/Tm3+/Ho3+)-alpha-sialon ceramic prepared by hot press sintering technique. Under 980 nm excitation, blue, green, red and near-infrared emissions are observed simultaneously as a result of the efficient energy transfer from Yb3+ to Er3+, Tm3+, and Ho3+ ions leading to a near-white light emission with CIE color coordinate of (0.38, 0.45). The two-and three-photon absorption processes are responsible for the observed upconversion emissions. The ceramic has moderately low phonon energy of 835 cm(-1). These novel properties make the material a promising candidate for upconversion applications. (C) 2017 Elsevier B.V. All rights reserved.</P>

Hierarchical material of carbon nanotubes grown on carbon nanofibers for high performance electrochemical capacitor

Kshetri, Tolendra,Thanh, Tran Duy,Singh, Soram Bobby,Kim, Nam Hoon,Lee, Joong Hee Elsevier 2018 CHEMICAL ENGINEERING JOURNAL -LAUSANNE- Vol.345 No.-

<P><B>Abstract</B></P> <P>The development of new advanced nanostructures based on the hybridization of different carbon nanomaterials to obtain enhanced performance of energy storage devices has attracted considerable attention. Herein, a hierarchical nanostructure of carbon nanotubes supported electrospun carbon nanofiber networks (CNTs@CNFs) was successfully fabricated by using two facile techniques: – electrospinning and chemical vapor deposition (CVD). Such CNTs@CNFs hybrid showed the uniform and high density of CNTs directly grown on the surface of carbon nanofiber networks, leading to the formation of a hierarchical nanostructure with a large surface area and highly porous characteristics. The enhanced interactions between the CNTs and the CNFs networks were found to improve the electrical conductivity and electrochemical stability of the material. Owing to its unique nanoarchitectures and physicochemical properties, the CNTs@CNFs hybrid was demonstrated to be a potential electrode material for an electrochemical capacitor, in which a high specific capacitance of 464.2 F g<SUP>−1</SUP> at 0.5 A g<SUP>−1</SUP> and long-term stability with 97% retention after 10,000 repeated charge–discharge cycles were achieved. The obtained results suggest that the present CNTs@CNFs hybrid is a promising candidate for an electrochemical capacitor in energy storage technologies.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A hierarchical nanostructure of CNTs@CNFs has been successfully fabricated. </LI> <LI> The CNTs@CNFs has large surface area and strong interfaces between hybrids. </LI> <LI> It shows a high specific capacitance of 464.2 F g<SUP>−1</SUP> at 0.5 A g<SUP>−1</SUP> and stability. </LI> </UL> </P>

Microwave hydrothermal synthesis and upconversion properties of Yb³⁺/Er³⁺ doped YVO₄ nanoparticles

Kshetri, Yuwaraj K,Regmi, Chhabilal,Kim, Hak-Soo,Lee, Soo Wohn,Kim, Tae-Ho IOP 2018 Nanotechnology Vol.29 No.20

<P>Yb<SUP>3+</SUP> and Er<SUP>3+</SUP> doped YVO<SUB>4</SUB> (Yb<SUP>3+</SUP>/Er<SUP>3+</SUP>:YVO<SUB>4</SUB>) nanoparticles with highly efficient near-infrared to visible upconversion properties have been synthesized by microwave hydrothermal process. Uniform-sized Yb<SUP>3+</SUP>/Er<SUP>3+</SUP>:YVO<SUB>4</SUB> nanoparticles were synthesized within 1 h at 140 °C which is relatively faster than the conventional hydrothermal process. Under 980 nm laser excitation, strong green and less strong red emissions are observed which are attributed to <SUP>2</SUP>H<SUB>11/2</SUB>, <SUP>4</SUP>S<SUB>3/2</SUB> to <SUP>4</SUP>I<SUB>15/2</SUB> and <SUP>4</SUP>F<SUB>9/2</SUB> to <SUP>4</SUP>I<SUB>15/2</SUB> transitions of Er<SUP>3+</SUP> respectively. The emission intensity is found to depend strongly on the concentration of Yb<SUP>3+</SUP>. The quadratic dependence of upconversion intensity on the excitation power indicates that the upconversion process is governed by two-photon absorption process.</P>

High performance asymmetric supercapacitor based on NiCo-layered double hydroxide (LDH) nanoneedle and activated carbon nanofibers.

박옥경,Tolendra Kshetri,김남훈,이중희 한국에너지학회 2018 한국에너지공학회 학술발표회 Vol.2018 No.11

IR to visible upconversion luminescence of transparent (Mg, Er)–α-Sialon ceramics

Joshi, Bhupendra,Kshetri, Yuwaraj K.,Adhikari, Rajesh,Wohn Lee, Soo Elsevier Science B.V., Amsterdam. 2015 CERAMICS INTERNATIONAL Vol.41 No.-

Green Luminescence in a Translucent (Mg, Yb)-<i>α</i>-Sialon Phosphor Under Blue Light Irradiation

Joshi, Bhupendra,Kshetri, Yuwaraj K.,Gyawali, Gobinda,Tripathi, Khagendra,Lee, Soo Wohn American Scientific Publishers 2018 Science of advanced materials Vol.10 No.1

<P>The translucent green alpha-Sialon ceramics was fabricated by the hot press sintering method. The fabricated alpha-Sialon ceramics co-doped with Yb2O3 shows green emission under blue light irradiation. The alpha-Sialon phase was the main phase obtained as observed by XRD. The effect of thicknesses on the optical properties was also analyzed. The green luminescence was observed at a 555 nm wavelength under 460 nm excitation. The thinner samples transmit higher blue light and hence show high luminous efficacy as coupled with the blue LED. Whereas, the 500 mu m thick sample shows green luminescence near the white region of CIE co-ordinates with a low luminous efficacy of 20.62l m/W.</P>

Insight into phosphate doped BiVO₄ heterostructure for multifunctional photocatalytic performances: A combined experimental and DFT study

Regmi, Chhabilal,Kshetri, Yuwaraj K.,Dhakal, Dipesh,Sohng, Jae Kyung,Rosei, Federico,Lee, Soo Wohn Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.466 No.-

<P><B>Abstract</B></P> <P>Doping with non-metals like phosphorous has been extensively investigated to extend radiation absorption and improve the photocatalytic efficiency of TiO<SUB>2</SUB>. However, the effect of non-metal doping in BiVO<SUB>4</SUB>, whose smaller bandgap (2.4 eV) allows for efficient visible light absorption, has been scarcely investigated. Visible light accounts for 45% of solar energy (as compared to only 5% of UV light) reaching the Earth’s surface. Due to its high efficiency in absorbing visible radiation, BiVO<SUB>4</SUB> can, therefore, be a promising material to replace TiO<SUB>2</SUB>. Here we demonstrate the synthesis of phosphate doped visible-light-active BiVO<SUB>4</SUB> by a microwave hydrothermal method as a promising alternative to TiO<SUB>2</SUB>. Subsequently, we investigated its photocatalytic activity for the removal of p-amino salicylic acid and ibuprofen, two cases of major pharmaceutical waste, as well as disinfection of multi-drug resistance <I>Staphylococcus aureus</I> bacteria. In addition, the biofilm elimination efficiency of the undoped and phosphate doped BiVO<SUB>4</SUB> was studied by crystal violet staining method. A 70% reduction in the biofilm biomass by phosphate doped BiVO<SUB>4</SUB> was obtained. Also, a 4.1log reduction in the viable cells count was observed within 180 min when <I>Staphylococcus aureus</I> was irradiated with visible light mixed in phosphate doped BiVO<SUB>4</SUB> powder. Under similar irradiation conditions, the degradation efficiency for p-amino salicylic acid and ibuprofen are 81% and 80% respectively, a 40% enhancement as compared to undoped BiVO<SUB>4</SUB>. First principle density functional theory calculations show that charge transfer from P to O in the doping site of the BiVO<SUB>4</SUB> is responsible for the enhanced photocatalytic activity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Phosphate doped BiVO<SUB>4</SUB> photocatalyst was prepared by a facile microwave-hydrothermal process. </LI> <LI> The catalyst was highly efficient for the degradation of the ibuprofen and p-amino salicylic acid. </LI> <LI> Effective inactivation of <I>S. aureus</I> bacteria under visible light was observed. </LI> <LI> Substantial inhibition of biofilm formation was observed in the presence of the photocatalyst. </LI> <LI> Underlying mechanism has been proposed through the DFT Calculation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Sunlight-driven sustainable production of hydrogen peroxide using a CdS–graphene hybrid photocatalyst

Thakur, Suman,Kshetri, Tolendra,Kim, Nam Hoon,Lee, Joong Hee Elsevier 2017 Journal of catalysis Vol.345 No.-

<P><B>Abstract</B></P> <P>We demonstrate the sustainable production of H<SUB>2</SUB>O<SUB>2</SUB> without organic electron donors by a CdS-reduced graphene oxide (RGO) photocatalyst in sunlight with water and oxygen as resources. Photocatalysts were prepared with various amounts of RGO (0–30wt.% with respect to CdS) by a hydrothermal method. A photocatalyst containing 20wt.% RGO (CdS-G2) showed maximum activity, and the amount of H<SUB>2</SUB>O<SUB>2</SUB> produced (128μM) was almost five times higher than that produced by CdS nanoparticles (27μM) after 12h sunlight irradiation. The results clearly revealed that the photocatalytic reactionmainly proceeds by two-electron reduction of oxygenrather than water oxidation on the catalyst surface. The effects of reaction temperature and pH on the production of H<SUB>2</SUB>O<SUB>2</SUB> were also investigated. We found that the production of H<SUB>2</SUB>O<SUB>2</SUB> was enhanced at lower temperature and pH. The concentration of H<SUB>2</SUB>O<SUB>2</SUB> reachedto 164 and 156μM with CdS-G2 at 10°C and pH 2, respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Preparation of CdS-based photocatalysts by a hydrothermal method. </LI> <LI> Production of hydrogen peroxide from water and oxygen. </LI> <LI> Temperature- and pH-dependent production of hydrogen peroxide. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>