Please use this identifier to cite or link to this item: http://hdl.handle.net/10266/6254
Title: Optical and structural properties of rare-earth doped calcium silicates derived from agro-food wastes
Authors: Kaur, Manmeet
Supervisor: Singh, Kulvir
Keywords: calcium silicate, agro-food wastes, optical materials, rare-earth oxides, phosphor
Issue Date: 4-Aug-2022
Abstract: Agriculture sector is expanding rapidly and is generating a significant amount of waste. Residues of crops like corn, rice, sugarcane, wheat are often burnt in open fields despite of the environmental implications. Along with the agriculture waste, huge portion of the total food produced is also being wasted. Without proper disposal mechanism this waste is left to rot by itself. From the perspective of environment and energy needs, the effective way to deal with the problem of waste management is to utilize these wastes to synthesize value-added products. Rice husk ash (RHA) and egg-shells (ES) are the most widely produced agro-food wastes. RHA and ES are found to be promising sources of SiO2 and CaCO3. Thus, RHA and ES are being used as resource materials to synthesize calcium silicate products. Calcium silicates have garnered a lot of interest because of their characteristic features like thermal and chemical stability, and transparency to visible light. Calcium silicates are considered good hosts for synthesizing rare-earth doped phosphors. Phosphors have become integral component of light emitting diodes which has resulted in extensive efforts by various researchers to develop highly efficient phosphor materials. Rare-earth doped phosphors produce emission in a wide range of the visible spectrum. Utilizing agro-food wastes as resource materials for synthesizing calcium silicate phosphor can be an effective approach of managing the widely available waste. The present work is based on the synthesis and characterization of rare-earth (Dy3+, Sm3+, and Eu3+) doped calcium silicates derived agro-food wastes like RHA and ES. The entire work is divided into the following six chapters: Chapter 1 describes the composition, extraction routes, and applications of the widely available agro-food wastes like RHA and ES. Structural properties of different calcium silicates (Ca2SiO4 and Ca3Si2O7) are presented describing their polymorphism. Interaction of solids with light, interband transitions, mechanism of energy transfer, and different components of phosphors are discussed to ensure detailed understanding of phosphor design. In addition, emission properties of rare-earth ions and applications of calcium silicate phosphors are also presented. Chapter 2 summarizes different factors affecting the room temperature stabilization of β − Ca2SiO4 phase. The photoluminescent properties of different rare-earth ion (RE3+) doped Ca2SiO4 and Ca3Si2o7 are presented to summarize the research on calcium silicate phosphors. Efforts by different researchers to synthesize RE3+ doped calcium silicates from agro-food wastes are also discussed. Last section presents the gaps in the study along with the objectives of the present research work. Chapter 3 presents details of the synthesis route followed for sample preparation and the material characterization techniques used to analyze the synthesized samples. The samples are synthesized via solid-state reaction technique using RHA and ES as sources of SiO2 and CaCO3. X-ray diffraction was used to analyze the crystal structure of the synthesized samples. Fourier-transform infrared spectroscopy and Raman spectroscopy are used to identify the structural units present in the samples. Energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy are used to study the composition of the samples. Morphology of the samples is studied using scanning electron microscope. Optical band of the samples is studied using UV-Visible spectroscopy and the luminescence properties are studied using fluorescence spectrophotometer. Chapter 4 discusses the structural, optical, and morphological properties of Ca2−xSiO4:xRE3+ (RE3+ = Dy3+, Sm3+, Eu3+, and x(mole%)=0.00, 0.25, 0.50, 0.75, and 1.00) prepared using RHA and ES. EDS results are utilized in order to replicate the composition of agro-food waste-derived (Ca2−xSiO4:xDy3+ x=0.75%) C2S75. Mineral oxide SiO2, CaO, Dy2O3, TiO2, Fe2O3, Na2O, Al2O3, and MgO are used to synthesize a sample similar to C2S75 via solid-state reaction method. The structural, morphological, and optical properties of the mineral-derived sample are also given in this chapter. Chapter 5 discusses the structural, optical, and morphological properties of Ca3−xSi2O7 : xRE3+ (RE3+ = Dy3+, Sm3+, Eu3+, and x(mole%)=0.00, 0.25, 0.50, 0.75, and 1.00) prepared using RHA and ES. Chapter 6 concludes the results presented in chapter 4 and 5. In the end, future scope of the present study is given.
URI: http://hdl.handle.net/10266/6254
Appears in Collections:Doctoral Theses@SPMS

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