Effect of ZnO Addition on the formation of Ag nanoparticles in Er3+ Doped Phosphate glasses
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Sinkkioksidin lisäämisen vaikutus hopeananopartikkelien muodostumiseen Er3+ doupatuissa fosfaattilaseissa
The purpose of this thesis was to investigate the impact of the glass composition on the formation of Ag nanoparticles in Er3+ doped phosphate glasses. The first task was to prepare Er3+ doped oxyfluoride phosphate glasses with varying glass compositions and to study the effect of the composition on the physical, structural, optical and spectroscopic properties of the glass. Glasses with the composition ((97x)*0.9NaPO3-(97-x)*0.1NaF-xZnO-2.5Ag2SO4-0.5Er2O3) with x =0, 1.25, 2.5, and 5 in mol% were prepared by standard melt quenching route. The glasses were melted in a quartz crucible for 5 minutes at temperatures ranging between 800°C and 875°C, depending on the glass composition and then annealed. Based on the DTA, all of the glasses are thermally stable as evidenced by their large T=Tx-Tg. The addition of ZnO increases the glass density and Tp, the crystallization temperature. Using IR and Raman spectroscopies, Zn is suspected to act as a modifier, leading to a depolymerization of the phosphate network and to a less cross-linked network. The addition of Zn increases the intensity of the emission band at 1.5 µm under pumping at 980nm although it has no noticeable impact on the site of Er3+. The second task was to grow silver nanoparticles (NPs) in the glasses using heat and to study the impact of the nanoparticles on the spectroscopic properties of the glasses. In order to grow silver NPs, the glasses were heat treated at a temperature of 10°C and 20°C above their respective glass transition temperature for 17 hours. The heat treatment changes the color of the glasses from pink to yellowish and so leads to the appearance of a new absorption band at ~400nm. This new band corresponds to the surface plasmon resonance (SPR) absorption of silver nanoparticles (NPs). The addition of ZnO was found to increase the intensity of the absorption band indicating that Ag NPs form more easily in a more depolymerized phosphate network. An increase in the intensity of the emission peak at 1530 nm was observed after heat treatment at Tg + 10°C due to the local field induced by SPR of Ag NPs and the energy transfer from metallic NPs to RE -ions. However, it is shown here that an increase in the heat treatment temperature to Tg + 20°C increases the intensity of the surface plasmon resonance absorption band of silver NPs indicating that a larger amount of Ag NPs are formed. However, the heat treatment decreases the intensity of the emission probably due to the back energy transfer from the exited states of Er3+ to the silver NPs. Finally, the X-ray diffraction analysis of the Tg + 20°C heat treated glasses confirms that the heat treatment does not lead to crystallization of the glasses.