Influence of ZnO content on liquid-liquid phase separation in photothermal refractive glass

•In this experiment, photo-thermo-refractive (PTR) glasses of Na-Zn-Al-Si system with ZnO contents of 2–6 mol% respectively were prepared by high-temperature melting, and the mechanism of the effect of ZnO on the liquid-liquid phase separation (LLPS) of the PTR glasses was investigated by using modern analytical test methods.•The LLPS in the samples was observed to be in the form of isolated droplets using SEM, the ZnO coordination number is affected by its own content, enabling us to observe the lowest point of the LLPS at a ZnO content of 4 mol%, when the glass formulation facilitates an increase in the transmittance and a reduction in the scattering losses of the optical glass.•The crystallisation component of PTR glass in this work is NaF, and the use of NaNO3 instead of the traditional method of using Na2CO3 to introduce the base component Na2O can avoid the generation of Ag2CO3 and Ag2O impurities and solve the problem of the difficulty of crystallisation of PTR glass.•The mechanism of LLPS in PTR glass: when the ZnO content is low, it tends to exist in the form of [ZnO4], and in order to balance the two negative charges generated by the [ZnO4] tetrahedra, it is necessary to list Zn2+ around them, thus prompting the occurrence of LLPS in PTR glasses; when the ZnO content is high, the stability of the glass is low, which promotes LLPS. At present, volume Bragg grating (VBG) is the core devices in the field of precision optical field modulation, and their performance is mainly influenced by the substrate photothermal refractive (PTR) glass. The liquid phase separation (LLPS) behavior occurring in the base glass can lead to unnecessary scattering losses and have adverse effects on the engineering applications of VBG. In recent years, many glass scientists have conducted research on the liquid-liquid phase separation (LLPS) of glass, believing that the structure of glass phase separation is related to the composition of the glass. This study used high-temperature melting method to prepare Na-Zn-Al-Si PTR glass doped with Ag, Ce, Sn and other elements through two-step heat treatment. In this experiment, the influence mechanism of ZnO on the LLPS of PTR glasses was investigated by controlling the doping amount of ZnO. Modern analysis techniques were used to investigate the mechanism of ZnO on the LLPS, the results confirm that no crystal phase is generated during the glass phase separation in this work, and doping 4 mol% ZnO is beneficial for suppressing t