الفهرس 
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Abstract
Upconversion materials are attracting considerable attention for their potential applications in different fields such as lasers, solar cells, color displays, optoelectronics, data storage technology and medical diagnostics. Upconversion materials, can convert low-energy incident radiation into higher energy emitted radiation. They are usually consisting of lanthanide ions doped different matrices (such as different crystal and glass types). Several mechanisms are involved in upconversion, including multiple photon absorption and energy transfers between dopants. Many reported upconversion materials in literature required quite high excitation thresholds while some required pumping with low power energies using commercial IR diode lasers or Xe-lamps depending on the dopants and the host. In this thesis, investigation has been carried out for upconversion in neodymium-doped SiO2–TiO2 using low energy excitation source. The SiO2–TiO2 system have been prepared by the sol–gel technique and doped with neodymium ions at different concentrations. The samples were heat treated and studied by TGA/DTA, FTIR and X-ray. The optical properties and upconversion of neodymium-doped SiO2–TiO2 system are presented.