Abstract
The influence of silver nanoparticles (Ag-NPs) on the optical properties of Bi2O3-GeO2 glasses was investigated aiming the characterization of their potential for applications in photonic devices. The samples were prepared by the melt-quenching technique starting from high purity oxides (GeO2, Bi2O3 and AgNO3). Heat-treatment during different times was performed to nucleate Ag-NPs. A transmission electron microscope was used to confirm the presence of Ag-NPs and to determine their sizes and composition. The glass network was studied by spontaneous Raman scattering. The optical absorption spectra showed an absorption band at ca. 500 nm associated to the bismuth ions, and a 7-fold enhancement of absorption was observed in the samples with Ag-NPs. Photoluminescence (PL) spectra were obtained by exciting the samples with a 808 nm laser. Maximum enhancements of ca. 100% of the PL band centered at 1300 nm and ca. 70% of the Raman spectrum were observed due to the nucleation of the Ag-NPs. The enhanced optical response of the samples with Ag-NPs is attributed to the growth of the local field on the isolated bismuth ions and clusters that are located in the vicinity of the nanoparticles. The results illustrate the large potential of Bi2O3-GeO2 with Ag-NPs to be used in photonic devices.
Highlights
In the Experimental section we describe the methods and techniques used for fabrication and characterization of the glasses
It can be seen a small decrease of the Bi2+ absorption band as reported for other bismuth doped glasses;[21,23] this change is negligible in comparison with the large increase observed for the samples with Ag-NPs
This is the first report that shows the influence of silver nanoparticles on the absorption spectrum, nearinfrared luminescence and Raman vibrational modes of the Bi2O3‐GeO2 glass
Summary
Heavy metal oxide (HMO) glasses are attracting large attention because of their linear and nonlinear optical properties that make them ideal candidates for applications such as ultrafast optical switches, optical limiters and active photonic devices.[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18] In general, besides low optical absorption in the visible and in the near-infrared (NIR) regions, the HMO glasses present high index of refraction (ca. 2.0), low cutoff phonon energies (ca. 800 cm-1), large polarizability, large resistance to moisture and good thermal stability that allow the fabrication of optical fibers. Samples with composition (in mol%): 86GeO2-14Bi2O3 and 80.4GeO2‐19.6Bi2O3 were prepared, without Ag‐NPs, and melted at 1100 oC and 1200 oC, for comparison with the optical response of the glass containing Ag-NPs. A 200 kV transmission electron microscope (TEM) was used to determine the sizes and shapes of the Ag-NPs. Energy dispersive X-ray spectroscopy was performed during the TEM analysis in order to confirm the presence of Ge, Bi and Ag-NPs. Electron diffraction measurements were performed to determine the crystalline structure of Bi NPs according to JCPDS-ICDD data base.[19] For these measurements the samples were milled, mixed with distilled water, and partially decanted.
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