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5. Up-converted white light emission in Er3+ doped MgAl2O4 nanocrystals.

Author

Savita, Murari Upadhyay, Madan, Bishnoi, Priyanka, Kumar, Sanjay, Kumar, Kaushal, Vij, Ankush, and Thakur, Anup

Subjects
NANOCRYSTALS, ANTISITE defects, CRYSTAL defects, NUCLEAR magnetic resonance, ION emission
Abstract

This work presents the influence of host defect centers on the photoluminescence characteristics of Mg 1 − x Er x Al 2 O 4 (x = 0.005, 0.01, and 0.03) nanocrystals under UV and near-infrared (NIR) excitations. The spinel-structured nanocrystals are synthesized through the combustion method. The Rietveld refinement and nuclear magnetic resonance analyses estimated the Er 3 + ion occupancy at octahedral and other random sites of the MgAl 2 O 4 lattice, and the existence of various lattice defects. Diffuse reflectance spectra showed broad bands attributed to oxygen vacancies as well as antisite defects and sharp peaks attributed to f–f transitions of Er 3 + ions. The upconversion luminescence spectra consisted of sharp emission lines, ascribed to Er 3 + ions, in the green and red wavelength regions, which overlapped over the broad curve attributed to intrinsic defects. Further, the UV excited downconversion luminescence spectra showed two broad emission bands in blue–violet and red-NIR regions with a very weak Er 3 + ion emission feature. This up- and downconversion emission revealed energy transfer between host and Er 3 + ions via intrinsic defects. As a result, the emission color changes from bluish purple to white by varying the excitation wavelength from UV to NIR. This rare earth activated luminescence from MgAl 2 O 4 nanocrystals would exhibit potential applications in display devices and solid-state lighting. [ABSTRACT FROM AUTHOR]

Published
2024
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6. Low temperature carrier transport mechanism and photoconductivity of WSe2

Author

Kaur, Manjot, Singh, Kulwinder, Chauhan, Ishant, Singh, Hardilraj, Sharma, Ram K, Vij, Ankush, Thakur, Anup, and Kumar, Akshay

Subjects
Condensed Matter - Materials Science
Abstract

This work reports the electrical transport and temperature-dependent photoconductivity in tungsten diselenide (WSe2) thin films. The electrical conductivity analysis shows the presence of the three regions with temperature variation. At lower temperatures (<190K), carriers become localized to small regions in the film due to the Mott hopping mechanism. The middle region (190 to 273 K) follows Seto parameters and obtained low barrier height (0.0873 eV) may be responsible for the improved carrier mobility. At higher temperature (>273K) region, thermally activated conduction is dominated with two activation energies of ~138 meV and 98 meV. The peaks obtained in photoluminescent analysis attributes to the presence of mid-bandgap states or defect states which play an important role in the photoconductivity of WSe2. The transient photoconductivity measurements show consistent temperature-dependent behaviour. The effect of light intensity and wavelength variation on the photoconductivity of WSe2 thin films is also discussed. The photocurrent is 1.19*10-5 A at 125 K while at 350 K it was observed to be 3.12*10-4 A. The light-on/off current cycles show that the current can recover to its initial state which points to the stable and outstanding reversible properties of the WSe2 thin film device to be used in photodetector applications., Comment: 17 Pages, 5 Figures

Published
2020
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11. Ga doping induced thermal stabilization of fcc phase in Ge2Sb2Te5 thin films: A step toward power-efficient phase change memories.

Author

Bala, Neeru, Goutam, U. K., and Thakur, Anup

Subjects
PHASE change memory, FACE centered cubic structure, THIN films, PHASE transitions, PHASE change materials, LIGHT transmission
Abstract

Ge 2 Sb 2 Te 5 (GST), a phase change material, generally exhibits two-step crystallization (amorphous → fcc → hcp) to store and process data. The present study reports the crystallization behavior and bonding mechanism of Ga-doped GST thin films with thermal annealing. Ga doping results in the formation of Ga–Te bonds and shows no bonding with other host elements (Ge and Sb), which changes the bonding mechanism and leads to one-step crystallization (amorphous → fcc). The optical transmission contrast confirmed the thermal stabilization of the fcc phase with thermal annealing. These findings suggest that Ga doping into GST thin films has thermally stabilized the metastable fcc phase and suppressed the hcp phase, hence posing it as a potential candidate for phase change memory applications with fast processing speed and low power consumption. [ABSTRACT FROM AUTHOR]

Published
2023
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38. Correspondence

Author

Kumar, Prawin, Goyal, Jagdish Prasad, Sankar, Janani, Dhanlakshmi, K., Khurana, Alkesh Kumar, Dhingra, Bhavna, Ramaswamy, Viraraghavan Vadakkencherry, Gummadapu, Sanghamitra, Modi, Manoj, Singh, Anchala, Thakur, Anup, Kler, Neelam, Bandyopadhyay, Tapas, Maria, Arti, Nimbalkar, Somashekhar M., Keerthy, Sharath, Nagesh, Karthik, Shah, Ira, and Shrigiriwar, Apurva

Published
2019
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41. Dysprosium site occupancy in SrZnO2 nanophosphors probed through XANES.

Author

Manju, Rajput, Parasmani, Vij, Ankush, and Thakur, Anup

Abstract

Doping-assisted lattice site engineering is widely practiced to obtain a tailor made response, which subsequently poses a need for an efficient probe of the local electronic structure of the system. This study presents a detailed analysis of the local electronic structure around the host cations (Zn2+ and Sr2+) and dopant (Dy3+) through combined experimental and simulated X-ray absorption near edge structure. The real space full multiple scattering-based simulations of the Zn K-edge are done by substituting Dy at cationic sites in the second coordination shell around Zn, in various combinations along with and/or without oxygen vacancies in the system. The results revealed that Dy tends to substitute the less symmetric Sr2+ site at low doping concentration, whereas it starts substituting the relatively more symmetric Zn2+ lattice site with an increase in doping concentration, consequently affirming the origin of cold white emission upon charge transfer in the system (Manju, M. Jain, P. Vashishtha, G. Gupta, A. Sharma, S. O. Won, A. Vij and A. Thakur, J. Phys.: Condens. Matter, 2020, 33, 035703). The effect of Zn site occupancy is seen as bifurcation of the single peaked Dy L3 absorption edge, which is usually reported as the sole indication of the existence of a mixed valence state. Thus, the combined analyses decipher the effect of lattice site occupancy on the local electronic structure of host as well as dopant atoms. [ABSTRACT FROM AUTHOR]

Published
2023
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45. Effect of silver doping on the electrical properties of a-Sb$_2$Se$_3$

Author

Gautam, Sanjeev, Thakur, Anup, Tripathi, S. K., and Goyal, Navdeep

Subjects
Condensed Matter - Materials Science
Abstract

This paper reports the effect of Ag-doping on electrical properties of a-Sb2Se3 in the temperature range 240-340 K and frequency range 5 Hz to 100 kHz. The variation of transport properties with thermal doping has been studied. Ag-doping produced two homogeneous phases in the sample and which are found to be voltage dependent in the temperature range studied and frequency dependent in lower frequency region (0.1 - 10 kHz). Activation energy Eg and C' [=$\sigma_0$ exp ($\gamma$/k), where $\gamma$, is the temperature coefficient of the band gap] calculated from dc conductivity has been found to vary from 0.42 eV to 0.26 eV and 41.08x10$^-6$ to 2.902x10-6 $\ohm^{-1}$cm$^{-1}$ respectively. Ag-doping can be used to make the sample more useful in device applications., Comment: 4 pages, 5 figures, Conference ISNOG 2006, IISc Bangalore(India)

Published
2006
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