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.

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>

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>

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>

Flexure of cross-ply laminated plates using equivalent single layer trigonometric shear deformation theory

Atteshamuddin S. Sayyad,Yuwaraj M. Ghugal 국제구조공학회 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.51 No.5

An equivalent single layer trigonometric shear deformation theory taking into account transverse shear deformation effect as well as transverse normal strain effect is presented for static flexure of cross-ply laminated composite and sandwich plates. The inplane displacement field uses sinusoidal function in terms of thickness coordinate to include the transverse shear deformation effect. The cosine function in thickness coordinate is used in transverse displacement to include the effect of transverse normal strain. The kinematics of the present theory is much richer than those of the other higher order shear deformation theories, because if the trigonometric term (involving thickness coordinate z) is expanded in power series, the kinematics of higher order theories (which are usually obtained by power series in thickness coordinate z) are implicitly taken into account to good deal of extent. Governing equations and boundary conditions of the theory are obtained using the principle of virtual work. The closed-form solutions of simply supported cross-ply laminated composite and sandwich plates have been obtained. The results of present theory are compared with those of the classical plate theory (CPT), first order shear deformation theory (FSDT), higher order shear deformation theory (HSDT) of Reddy and exact three dimensional elasticity theory wherever applicable. The results predicted by present theory are in good agreement with those of higher order shear deformation theory and the elasticity theory.

Flexure of cross-ply laminated plates using equivalent single layer trigonometric shear deformation theory

Sayyad, Atteshamuddin S.,Ghugal, Yuwaraj M. Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.51 No.5

An equivalent single layer trigonometric shear deformation theory taking into account transverse shear deformation effect as well as transverse normal strain effect is presented for static flexure of cross-ply laminated composite and sandwich plates. The inplane displacement field uses sinusoidal function in terms of thickness coordinate to include the transverse shear deformation effect. The cosine function in thickness coordinate is used in transverse displacement to include the effect of transverse normal strain. The kinematics of the present theory is much richer than those of the other higher order shear deformation theories, because if the trigonometric term (involving thickness coordinate z) is expanded in power series, the kinematics of higher order theories (which are usually obtained by power series in thickness coordinate z) are implicitly taken into account to good deal of extent. Governing equations and boundary conditions of the theory are obtained using the principle of virtual work. The closed-form solutions of simply supported cross-ply laminated composite and sandwich plates have been obtained. The results of present theory are compared with those of the classical plate theory (CPT), first order shear deformation theory (FSDT), higher order shear deformation theory (HSDT) of Reddy and exact three dimensional elasticity theory wherever applicable. The results predicted by present theory are in good agreement with those of higher order shear deformation theory and the elasticity theory.

An inverse hyperbolic theory for FG beams resting on Winkler-Pasternak elastic foundation

Sayyad, Atteshamuddin S.,Ghugal, Yuwaraj M. Techno-Press 2018 Advances in aircraft and spacecraft science Vol.5 No.6

Bending, buckling and free vibration responses of functionally graded (FG) higher-order beams resting on two parameter (Winkler-Pasternak) elastic foundation are studied using a new inverse hyperbolic beam theory. The material properties of the beam are graded along the thickness direction according to the power-law distribution. In the present theory, the axial displacement accounts for an inverse hyperbolic distribution, and the transverse shear stress satisfies the traction-free boundary conditions on the top and bottom surfaces of the beams. Hamilton's principle is employed to derive the governing equations of motion. Navier type analytical solutions are obtained for the bending, bucking and vibration problems. Numerical results are obtained to investigate the effects of power-law index, length-to-thickness ratio and foundation parameter on the displacements, stresses, critical buckling loads and frequencies. Numerical results by using parabolic beam theory of Reddy and first-order beam theory of Timoshenko are specially generated for comparison of present results and found in excellent agreement with each other.

Thermoelastic bending analysis of laminated plates subjected to linear and nonlinear thermal loads

Swami, Sandhya K.,Ghugal, Yuwaraj M. Techno-Press 2021 Advances in aircraft and spacecraft science Vol.8 No.3

The paper presents the analytical solutions for thick orthotropic laminated plates using trignometric shear deformation theory. The effects transverse shear and transverse normal strains are included with linear and nonlinear thermal loads. The displacement field of the theory includes the trigonometric functions in thickness coordinate of plate to account for these effects. The displacement field enforces to give the realistic variation of shear stresses across the thickness of plate and thus obviates the need of shear correction factor. The main novelty of the present study is the inclusion of thickness stretching effect in the theory. Another novelty is the application of nonlinear thermal profile consistent with the displacement field of the theory. The principle of virtual work is used to obtain the governing equations and boundary conditions. Simply supported laminated square plates are considered for numerical study to evaluate thermoelastic response. The results obtained by present theory with thickness stretching effect are compared with other refined theories disregarding this effect. It is observed that the results of present theory deviate significantly from the results of other higher order shear deformation theories for antisymmetric crossply laminated plates. The results of symmetric cross-ply laminated plates subjected to linear sinusoidal thermal load are in close agreement with those of exact theory, which validates the accuracy of present shear and normal deformation theory.

Cylindrical bending of multilayered composite laminates and sandwiches

Sayyad, Atteshamuddin S.,Ghugal, Yuwaraj M. Techno-Press 2016 Advances in aircraft and spacecraft science Vol.3 No.2

In a whole variety of higher order plate theories existing in the literature no consideration is given to the transverse normal strain / deformation effects on flexural response when these higher order theories are applied to shear flexible composite plates in view of minimizing the number of unknown variables. The objective of this study is to carry out cylindrical bending of simply supported laminated composite and sandwich plates using sinusoidal shear and normal deformation plate theory. The most important feature of the present theory is that it includes the effects of transverse normal strain/deformation. The displacement field of the presented theory is built upon classical plate theory and uses sine and cosine functions in terms of thickness coordinate to include the effects of shear deformation and transverse normal strain. The theory accounts for realistic variation of the transverse shear stress through the thickness and satisfies the shear stress free conditions at the top and bottom surfaces of the plate without using the problem dependent shear correction factor. Governing equations and boundary conditions of the theory are obtained using the principle of minimum potential energy. The accuracy of the proposed theory is examined for several configurations of laminates under various static loadings. Some problems are presented for the first time in this paper which can become the base for future research. For the comparison purpose, the numerical results are also generated by using higher order shear deformation theory of Reddy, first-order shear deformation plate theory of Mindlin and classical plate theory. The numerical results show that the present theory provides displacements and stresses very accurately as compared to those obtained by using other theories.

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>