الفهرس 
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Abstract
Rare-earth ions are popular dopants for solid-state lasers due to their long upper-level lifetimes, ability to generate short pulses, and straight forward incorporation into host materials including glasses and crystals. The common characteristic of the rare earth (RE) metals is their partially-filled 4f shell. They often form trivalent ions whose properties are generally more important than those of neutral atoms. The most remarkable feature of the rare earth (RE) ions in solid-state host is the sharpness of many absorption and emission spectral lines which are as narrow as the spectra of free atoms. Among all lanthanide (III) ions interest is especially focused on Eu3+ and Sm3+ ions, europium has attracted significant attention as a luminescent active ion with an intense red emission coming from its 5D0_ 7F2 transition. The Eu3+ ion has the great advantage over other lanthanide ions with an even number of 4f6 electrons that the starting levels of the transitions in both the absorption and the luminescence spectrum are non-degenerate (J = 0). Moreover, the interpretation of the spectra is facilitated by the small total angular momentum J of the end levels in the transitions. The number of lines observed for the5D0_7FJ transitions in the luminescence spectrum or the 5DJ_7F0 transitions in the absorption spectrum allows determining the site symmetry of the Eu3+ion. Sm3+ (4f5) ion is one of the most interesting ions to analyze the fluorescence properties because of its use in highdensity optical storage, under sea communication and color displays. Its emitting 4G5/2 level exhibits relatively high quantum efficiency and also shows different quenching emission channels. The sol-gel method has been reported to have more advantages over other wet chemistry and conventional glass processing methods because it has the potential to produce materials with high purity and homogeneity at low temperatures. It extends the traditional glass melting processes by allowing incorporation of semiconductor and rare-earth ions at low temperatures and predetermined concentrations in different hosts in such a way that the size and shape of the particles can be controlled during the growth and nucleation processes. A major problem with monolithic gels is cracking during ageing and drying. Several approaches have been suggested to obtain monolithic gels. One of the objectives of this study is to demonstrate the possibility of producing monolithic silica gel using ethylene glycol (EG). According to the results of this study, EG drying control chemical additive is suitable for use in improving the characteristics of silica gels prepared from tetraethylorthosilicate solution. We found that the addition of EG increase the solubility of the lanthanide ions in this host, which leads to more transparency of the silica gels and make it accept higher concentrations of rare earth, reduce the cracking, increase the average pore size of densified sol-gels, increase the absorption and emission intensity, and allow more transitions to occur. Sol-gel silica glasses were fabricated using two different preparations to vary EG content. The sol of samples fabricated without EG was prepared according to common sol gel method while the sol of samples fabricated with EG was prepared according to the modified procedure. Rare earth (RE)-doped wide bandgap semiconductors have been extensively studied for potential use in integrated optoelectronic devices such as visible (blue, green, and red) and infrared luminescent devices. Zinc oxide is a very important semiconductor with a wide direct bandgap (3.37 eV), with large binding exciton energy (60 meV) at room temperature. In particular, doping of zinc oxide with optically active RE ions, allows the fabrication of devices that can emit light of different wavelengths from the UV to the visible range. In this work, different concentrations of RE3+ (Eu3+, Sm3+) ions were successfully synthesized via two procedures traditional sol-gel method and modified sol gel method to produce transparent rare earth samples having no cracking and to select the optimum concentration which then doped with different concentrations of ZnO (as sensitizer) via modified sol-gel method to produce rare earth composite zinc oxide. The concentration 2.5% wt. was selected as optimum concentration of Eu3+ and Sm3+.The optimum concentration of ZnO was selected to be 0.625% wt. and 0.25%wt. for Eu3+ and Sm3+ doped sol gel silica glass respectively. The spectroscopic tests of the final samples, which are involved absorption and fluorescence spectra, give us primary indications about the behavior of rare earth molecules inside the sol-gel matrices and the energy levels structure. from a theoretical point of view, Judd-Ofelt theory is regarded as a powerful tool for obtaining information on the local-environmental characteristics around an RE ion, such as spatial symmetry, covalency between an RE ion and the ligand, and electronic distribution, in sol gel glass. In this work, the Judd-Ofelt analysis will be performed for the purpose of calculating laser parameters like spontaneous emission probability, Fluorescence branching ratio, Radiative lifetime and stimulated emission cross section have been calculated by using the emission wavelength, reduced transition positions and cross- sections, transition probabilities, matrix elements for the transition and the values of Judd-Ofelt parameters. This data is essential to design optical devices such as lasers, color displays, up converters, and fiber amplifiers and so on.