Evolution of microstructure and spectral characteristics of silver nanoparticles in photo-thermo-refractive glass

Photo-thermo-refractive (PTR) glass is widely used in volume holographic devices. After photo-thermo treatment, silver nanoparticles (Ag-NPs) and sodium fluoride (NaF) crystals can precipitate in the glass matrix to realize refractive index modulation (RIM). The Ag-NPs are the foundation for subsequent precipitation of NaF crystals and significantly affect the absorption and luminescence characteristics of PTR glass. Within the nucleation temperature range of 440 degrees C-480 degrees C, the Ag-NPs formed by photo-thermo-induced nucleation are within 5 nm. Increasing nucleation heat treatment time causes an increase in the average size of Ag-NPs and the thickness of AgBr shell. Increasing the UV exposure dose significantly increases the concentration of Ag-NPs. The long nucleation time and high UV exposure doses can both increase the content of luminescent silver molecular cluster [Agm]n+, while high nucleation temperatures over 500 degrees C cause fluorescence quenching of PTR glass due to the formation of large Ag-NPs over 10 nm and NaF crystals. The formation of Ag-NPs effectively reduces the crystallization temperature of PTR glass. The refractive index of PTR glass can be effectively controlled by adjusting the parameters of photo-thermo-induced nucleation. Under the condition of crystallization at 550 degrees C for 30 min, a maximum RIM value of 1500 ppm can be achieved.