Department Of Physics

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Probing the optical and magnetic modality of multi core-shell Fe3O4@SiO2@?-NaGdF4:RE3+ (RE = Ce, Tb, Dy) nanoparticles
(Elsevier B.V., 2023-02-22T00:00:00) Shrivastava, Navadeep; Ospina, Carlos; Jacinto, Carlos; de Menezes, Alan S.; Muraca, Diego; Javed, Yasir; Knobel, Marcelo; Luo, Zhiping; Sharma, Surender Kumar
A robust yellowish-green emitting multi core-shell Fe3O4@SiO2@?-NaGdF4:RE3+ (RE = 5% Ce, 5% Tb, x% Dy; x = 1, 5 and 10 mol.%) nanoparticles (NPs) containing both magnetic and luminescence modalities, are synthesized using simple, fast and efficient microwave-assisted hydrothermal method. The Rietveld analysis of X-ray diffraction and high-resolution transmission electron microscopy provides an average crystallite size of ?30 nm, confirming the successful coating of the ?-NaGdF4 hexagonal phase over Fe3O4. The detailed photoluminescence investigation suggests a down-converting energy transfer process, Ce3+?Gd3+?Tb3+? Dy3+ in which Gd3+ ions play a significant intermediate role assisted by Tb3+. The excitation spectra consist of dominant broadband at ?252 nm due to Ce3+ (4f�5d), two sharp lines at ? 271 nm, and ?311 due to Gd3+ (8S7/2?6IJ and 6PJ), and frail f?f transitions due to Tb3+ and Dy3+ ions. The excitation at ?252 nm fetches weak and sharp emission of Gd3+ ions at 310 nm, weak broad emission of Ce3+ (300�400 nm), and strong emission color lines of RE3+ (400�700 nm) due to characteristic transitions of Tb3+ (5D4?7FJ, J = 6�3), and Dy3+ (4F9/2�6H15/2, 6H13/2), respectively. The quenching phenomenon is observed due to concentration, and back transfer energy is proposed. The magnetic hysteresis loops display superparamagnetic behavior at 300 K and ferromagnetic ordering at 2 K with a remarkable difference in their magnetization values and confirming the blocking temperatures around physiological temperature ranges. The magneto-luminescence characteristics of the bifunctional system can be easily manipulated under an external magnetic field and suggest an efficient candidate for hybrid medical imaging such as MRI plus X-ray imaging and radiation detection. � 2023 Elsevier B.V.
Scopes of laser in spectroscopy
(Elsevier, 2023-01-27T00:00:00) Verma, Dalip Singh; Shrivastava, Navadeep; Sharma, Surender Kumar
Spectroscopy deals with the interaction of light radiation with matter, which provides information on the structure and properties of matter (solids, liquids, and gasses). If laser light is used in place of the light radiation, then the spectroscopy is known as laser spectroscopy. Laser spectroscopy has emerged as a tool in many scientific techniques like tracking air quality, process control, medical research, national security, agriculture, artwork authentication, and many more. This is due to the special characteristics of lasers as compared to ordinary light. Although the emission of laser radiation is governed by the same rules and principles as that of any other light sources, laser light is not like any other ordinary source of radiation found in nature. It is a much more powerful technological tool than light from ordinary sources. Its features like coherence, monochromaticity, and collimation (directionality or low-beam divergence) make it special. The laser beam emerging from the output mirror of the resonant cavity is highly parallel, and its divergence (the spread in a beam of light) is typically a few milliradians, that is, negligibly small. The photons emitted even at a slight angle with respect to the tube axis bounce back into the walls of the tube and do not contribute to the output beam (not 100% true due to diffraction). The laser cavity is resonant only for the frequencies ?=nc/2d, where d is the separation between the mirrors of the resonant cavity adjusted as an integral of half of the wavelength, limiting the wavelength range (production of laser of well-defined wavelength). The intensity of the laser, defined as the power emitted per unit area of the output mirror per unit solid angle, is extremely high compared with that of a conventional source. The conventional sources of radiation are incoherent in nature, which means that any two photons of the electromagnetic waves of the same wavelength are out of phase, while the laser is both temporally and spatially coherent, which means that the coherence of the laser medium exists for a relatively long time and over a relatively large distance. Laser, by virtue of its coherent nature, is used for local heating, as in metal cutting, metal welding, and for holography. The coherent nature of the laser is by virtue of the mechanism through which it is produced, that is, the process of stimulated emission where photons are essentially copied or exactly in phase. The production of laser in the same phase takes place as all emitted photons are at exactly the same wavelength due to the transition between two fixed energy levels (the amplification mechanism of the laser). The simplest explanation for these properties of the laser is in the mechanism of the laser itself. The process mainly includes the stimulated emission, which takes place in the amplifying medium contained by the laser. This is done with the application of a set of mirrors used for feeding the light back to the amplifying medium so that the developed beam is grown continuously. The key concept for the realization of the laser operation is the principle of coherence accompanying stimulated emission. This stimulated emission needs the process of population inversion, for which the lasing medium must have at least three energy levels. � 2023 Elsevier Ltd. All rights reserved.
Modern Luminescence from Fundamental Concepts to Materials and Applications: Volume 1: Concepts of Luminescence
(Elsevier, 2023-01-27T00:00:00) Sharma, Surender Kumar; da Silva, Carlos Jacinto; Garcia, Daniel Jaque; Shrivastava, Navadeep
Modern Luminescence: From Fundamental Concepts to Materials and Applications, Volume One, Concepts and Luminescence is a multivolume work that reviews the fundamental principles, properties and applications of luminescent materials. Topics addressed include key concepts of luminescence, with a focus on important characterization techniques to understand a wide category of luminescent materials. The most relevant luminescent materials, such as transition metals, rare-earth materials, actinide-based materials, and organic materials are discussed, along with emerging applications of luminescent materials in biomedicine, solid state devices, and the development of hybrid materials. This book is an important introduction to the underlying scientific concepts needed to understand luminescence, such as atomic and molecular physics and chemistry. Other topics explored cover the latest advances in materials characterization methods, such as Raman spectroscopy, ultrafast spectroscopy, nonlinear spectroscopy, and more. Finally, there is a focus on the materials physics of nanophotonics. � 2023 Elsevier Ltd. All rights reserved.

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