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Understanding the luminescence in Yb3+ co-doped Sialon: Eu2+/Eu3+ transparent phosphor ceramic plate
Bhupendra Joshi,GYAWALI GOBINDA 한국세라믹학회 2022 한국세라믹학회지 Vol.59 No.3
The transparent Sialon phosphor ceramic plates were fabricated with varying amounts of Yb2O3 and Eu2O3. The hot press sintering technique was used to sinter the compact powders. The fabricated samples with the highest Yb2O3 concentration (10 wt%) and lowest Eu2O3 concentration (1 wt%) show a dominant α-Sialon phase, whereas the highest Eu2O3 (8 wt%) and lowest Yb2O3 (3 wt%) containing sample shows composite α/β-Sialon phases as confirmed by the XRD analysis. The light transmittance was measured for 0.1 mm thick samples. The maximum light transmission of 60% was observed at 800 nm wavelength for the highest Yb2O3 added Sialon ceramics. Also, the higher Yb2O3 and lower Eu2O3 containing samples show a sharp orange luminescence at 590 nm, attributed to the parity allowed magnetic dipole induced 5D0 → 7F1 transition of the Eu3+. These samples also produced upconversion luminescence as irradiated by 980 nm wavelength. The sample with the highest Eu2O3 addition exhibits broad greenish-yellow down-conversion emission with a sharp emission at 590 nm for composite α/β-Sialon phases. The recorded broad emission ranges from green to red, offering a wide spectrum of visible light for lighting applications.
Ce3+ and Eu2+ doped Sialon dual phosphor ceramic plates for white light emitting diodes
Bhupendra Joshi,Gobinda Gyawali 한양대학교 세라믹연구소 2020 Journal of Ceramic Processing Research Vol.21 No.6
Recent studies on transparent polycrystalline phosphor ceramic plates (PCPs) show its potential application in high brightnesslaser lighting. Herein, we explore the luminescence properties of Ce3+ cation in transparent Sialon phosphor ceramic plate. Thegreen luminescence was observed in Ce3+ doped Sialon PCP as excited by the 390 nm wavelength. Also, the redshift ofemissions was observed when the excitation wavelength was modulated from UV to blue light. The matrix phases and latticeparameters of Sialon PCPs were analyzed by XRD. The co-doping of Y3+ cations resulted a composite α/β-Sialon phase whiledoping with Gd3+ produced a higher α-Sialon phase. Higher transparency was observed with Gd3+ co-doped sample withgreenish-yellow luminescence under blue light excitation. The optical properties of Gd-α-Sialon: Eu2+ was also investigated. Moreover, a broadband white light was obtained after placing Gd-α-Sialon: Eu2+ on the top of the Gd3+/Ce3+ doped Sialon asa dual plate under blue LED excitation.
Bhupendra Joshi,KSHETRI YUWARAJ KHATRI,Gobinda Gyawali,이수원 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.3
The novel Er3+ and Yb3+ doped transparent Sialon ceramics were fabricated by hot pressing sintering method as a nearinfrared (NIR) as well as visible luminescent material. The optical transmittance, down-conversion luminescence and NIRluminescence were investigated. The samples show around 30% transmittance in visible region whereas 70% in IR regionaround 3000 nm. The samples were excited within the range of 350-400 nm wavelength, the highest emission was in greenregion (~ 550 nm). Also, the upconversion luminescence depending upon the thicknesses of the samples in the green and redregion have been investigated. The NIR luminescence was observed around 1524 nm wavelength under 980 nm wavelengthirradiation. The decay time profiles have been investigated for higher Er3+ concentration and higher Yb3+ co-doped with Er3+α-Sialon samples. In this study, the addition of Yb3+ has poor sensitizing effect on Er3+ ion to enhance the luminescence.
Joshi, Bhupendra,Regmi, Chhabilal,Dhakal, Dipesh,Gyawali, Gobinda,Lee, Soo Wohn Elsevier 2018 Progress in natural science Vol.28 No.1
<P><B>Abstract</B></P> <P>One dimensional titanate nanotubes (TNTs) were synthesized by microwave assisted alkaline hydrothermal process. The process was followed by UV-photodeposition of Ag and Cu on the surface of TNTs to enhance the photocatalytic activity in visible light spectrum. The loading of Ag and Cu (single and combination mode) offered a new insight to inactivate multi-drug resistant micro-organisms. The antibacterial properties of these samples were studied on Gram positive bacteria, <I>Staphylococcus aureus</I> (<I>S. aureus</I>) using well diffusion method. The TNTs with Ag and Cu loading showed a clear zone of inhibition after overnight incubation of <I>S. aureus</I>. The bacterial inactivation efficiency of nanoparticles in the visible light was further analyzed by kill kinetics. TNTs with Ag and/or Cu loading showed a significant reduction in bacterial growth. Cu co-loaded with Ag sample showed the highest inactivation efficiency within 90 min of visible light irradiation. To elucidate the mechanism of bactericidal properties of samples under visible light irradiation, the formation of reactive oxygen species (ROS), particularly, superoxide radical anion was determined by nitro blue tetrazolium (NBT) assay and the protein degradation by each samples were measured. Based on overall results, it was observed that the Cu co-loaded with Ag on TNTs samples were found to be more effective as compared to either Ag or Cu loaded TNTs. It provides new avenues for utilizing the combination of Cu and Ag for enhancing the antimicrobial efficacies for different nanoparticles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Antibacterial property and photoinactivation of <I>S. aurues</I> by Ag and Cu loaded TNTs. </LI> <LI> Almost complete <I>S. aureus</I> inactivation was found with combined Ag and Cu loaded TNTs in 90 min. </LI> <LI> The generation of superoxide radical ion and protein degradation was analyzed to elucidate the killing mechanism. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Optical, Mechanical and Tribological Properties of Boronnitride Dispersed Silicon Nitride Ceramics
Joshi, Bhupendra,Fu, Zhengyi,Niihara, Koichi,Lee, Soo-Wohn Materials Research Society of Korea 2010 한국재료학회지 Vol.20 No.8
Transparent ceramics are used in new technology because of their excellent mechanical properties over glasses. Transparent ceramics are nowadays widely used in armor, laser windows, and in high temperature applications. Silicon nitride ceramics have excellent mechanical properties and if transparent silicon nitride is fabricated, it can be widely used. h-BN has a lubricating property and is ductile. Therefore, adding h-BN to silicon nitride ceramics gives a lubricating property and is also machinable. Translucent silicon nitride was fabricated by hot-press sintering (HPS) and 57% transmittance was observed in the near infrared region. A higher wt. % of h-BN in silicon nitride ceramics does not favor transparency. The optical, mechanical, and tribological properties of BN dispersed polycrystalline $Si_3N_4$ ceramics were affected by the density, ${\alpha}:{\beta}$-phase ratio, and content of h-BN in sintered ceramics. The hot pressed samples were prepared from the mixture of $\alpha-Si_3N_4$, AlN, MgO, and h-BN at $1850^{\circ}C$. The composite contained from 0.25 to 2 wt. % BN powder with sintering aids (9% AlN + 3% MgO). A maximum transmittance of 57% was achieved for the 0.25 wt. % BN doped $Si_3N_4$ ceramics. Fracture toughness increased and wear volume and the friction coefficient decreased with an increase in BN content. The properties such as transmittance, density, hardness, and flexural strength decreased with an increase in content of h-BN in silicon nitride ceramics.
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>