STRUCTURAL AND OPTICAL PROPERTIES OF PYROCHLORE STRUCTURED MATERIALS

Abstract

The main focus of this thesis is to examine the optical and structural properties of materials with rare earth ions doped pyrochlore structures that were created using the conventional solid state approach. The main idea in the work is to enhance the luminescence phenomenon via doping of various rare earth ions in the host. It explores how the structural and optical properties of Gd2Ti2O7 pyrochlore are affected by rare earth ions doping at both the A and B sites. Numerous applications are now available because of the recent developments in solid-state lighting (SSL) technology. It is possible to create phosphor-based white LEDs with a single yellow phosphor and a blue LED chip, or with a combination of red, green, and blue phosphors stimulated by a UV LED chip. Low colour saturation, a lower colour rendering index (CRI), and an unstable colour temperature can result from the first method’s red-green phosphor’s reabsorption of blue light and the later method absence of a red component In order to overcome these obstacles, single-phase phosphors doped with particular combinations of rare earth ions such as Dy3+ , Eu3+ , Ce3+, Sm3+ etc. must be developed. This will enable the energy transfer necessary to produce white light emission. Furthermore, in order to enhance performance metrics such as correlated colour temperature (CCT), CRI, and luminous efficiency, new red phosphors are required.. Because of their adaptable physical, chemical, and luminous qualities, these phosphors are used in solar cells, biosensing, and other optoelectronic devices in addition to lighting. Phosphorus materials are often composed of a crystalline host matrix and an activator, or luminous centre. These materials are thought to be necessary for the development of white LED’s and agricultural lighting systems. Due to the distinct luminous characteristics of rare earth ions, xii inorganic phosphors activated by RE ions have been the preferred option for producing LEDs in recent decades. Transitions between the partially filled 4f energy levels of rare earth ions are made possible in these phosphors by the interaction between the orbitals of the rare earth ions and the oxygen atomic orbitals in the host, which produces unique luminous features. Titanate pyrochlores are one of the many inorganic oxides that have acquired popularity for use in luminescent devices because of their good physical and chemical stability, wide range of excitation wavelengths, and abundance of bright colours. Pyrochlore oxides Gd2Ti2O7 host are also reasonably priced, and their preparation techniques need less energy. Because of presence of rare earth ion at the A-site of pyrochlore structure Gd2Ti2O7, the accommodation of another rare earth ion at the place of Gd is easier as the cation radii of various rare earths ions are nearly equal, these generate broadband visible light, which can enhance associated colour temperature and colour rendering. By regulating the energy transfer from Gd to rare earth ions, it is possible to get tunable visible emissions in rare earth-activated pyrochlore oxides, as recent studies have shown. Gd2Ti2O7 is renowned for its exceptional optical properties when doped with suitable rare earth ion, displaying quantum features along with amazing enhanced luminescence. This host may be made to emit various colours in the visible spectrum by adding the right rare earth ions, which makes it appropriate for LEDs used in agricultural lighting and general illumination applications. To accomplish the research goals, this work is divided into seven chapters that include comprehensive structural, and photoluminescence characterizations.