Thick Er-doped silica films sintered using CO2 laser for scintillation applications

In this work, we demonstrated the fabrication of crack-free luminescent Er-doped silica coatings sintered using a CO2 laser. The silica sol-gel precursor with controllable rheology was developed using tetraethyl orthosilicate (TEOS) and hexamethyldisiloxane (HMDS). Luminescence activation was achieved through doping with Er ions. Coatings sintered at 1100 °C presented green photoluminescence at ∼550 nm and strong radioluminescence as well. After dip-coating, crack-free Er-doped silica thin films were obtained using a CO2 laser. Films sintered by laser had similar microstructure as the films sintered in a furnace. However, laser sintering extended the thickness range for making crack free sintered films. Using laser sintering, the thickness of crack-free silica films could be extended to above 1 μm, which is important for scintillation and optical waveguide applications. In order to understand the cracking control mechanism, a finite element (FEM) model was developed to analyze the stress distribution within the laser-sintered thin film. The model showed that the localized nature of sintering by laser heating allows for constrained sintering stress relaxation by the softer surrounding region of the film, effectively suppressing cracking.