Quantum and dielectric confinements of sub-10 nm gold in dichroic phosphate glass nanocomposites

•We fabricated Au0 embedded nanocomposites in P2O5–SnO–ZnO glass matrix.•Au0 synthesized by a single step in-situ thermochemical reduction technique.•We have reported the blue shifts of the SPR band of sub-10 nm Au0 NPs.•The optical property has been explained on the basis of electrodynamics theories.

Blue shifts of the surface plasmon resonance band of sub-10 nm gold in dichroic phosphate glass nanocomposites are observed with increase in both size of gold nanoparticles and refractive index of the medium, which are contrary to the common trends. These phenomena have been enlightened with the electrodynamics theories (Mie and Drude models) and happened due to quantum and dielectric confinements. Nanocomposites have been synthesized by in-situ thermochemical reduction technique in reducing phosphate glass matrices. The plasmon bands are characterized by the UV–vis spectrophotometer, and shape and size of the nanogold by the transmission electron microscopy. All the nanocomposites are dichroic in nature.