Effect of alkali metal ion doping on the optical and morphological properties of translucent SiO₂ pellets
This paper presents a synthesis route and post-sintering of pure and alkali metal (Li, Na, K) doped SiO2 nanoparticles, with a focus on obtaining transparent amorphous SiO2 pellets. Adding Li ions leads to translucent SiO2 pellets and decreases the SiO2 nanoparticle processing temperature. Sol-gel s...
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| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Elsevier
2025-07-01
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| Series: | Next Materials |
| Subjects: | |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S2949822825004472 |
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| Summary: | This paper presents a synthesis route and post-sintering of pure and alkali metal (Li, Na, K) doped SiO2 nanoparticles, with a focus on obtaining transparent amorphous SiO2 pellets. Adding Li ions leads to translucent SiO2 pellets and decreases the SiO2 nanoparticle processing temperature. Sol-gel synthesis method was used in this study to obtain nanostructured and porous SiO2 nanoparticles. The morphology and optical properties of the prepared SiO2 pellets were studied to show the influence of the alkali metal doping effect on the formation of point defects, particularly non-bridging oxygen hole centers (“NBOHC”). Li-doped SiO2 nanoparticles showed a smaller average particle size distribution. In contrast, the Na and K-doped SiO2 nanoparticles lead to white and opaque SiO2 pellets, with larger average particle size and coarser particle morphology, leading to increased scattering of light. We obtained translucent and porous SiO2 pellets by pressing heat-treated Li-doped SiO2 nanoparticles at room temperature. To study the doping effect of alkali metal ions, conventional synthetic “wet” SiO2 glass (Suprasil) and commercially available fumed silica nanoparticles (Aerosil® EG 50, Degussa) were used for comparison. Raman spectra for alkali-doped SiO2 samples showed the presence of a sharp (FWHM=8 cm−1) band at ∼978 cm−1 and a band at 3746 cm−1 due to ''free'' (not H-bonded) silanol ≡Si−O-H groups, characteristic to SiO2 surfaces. The K and Na doped SiO2 pellets showed a large concentration of 3-membered Si-O rings (signal at 606 cm−1) with increasing the alkali-metal ion concentration (from 0.1 at% to 2.0 at%), and a signal at 485 cm−1 due to 4-membered Si-O rings. These results indicate the formation of nano-pores in the structure, particularly for K and Na-doped SiO2 nanoparticles, contributing to their opacity. X-ray luminescence (XRL) measurements showed signals related to the formation of the intrinsic defect – a signal at 1.9 eV due to NBOHC, providing further evidence of alkali metal presence. |
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| ISSN: | 2949-8228 |