Thermally-induced precipitation of gold nanoparticles in phosphate glass: effect on the optical properties of Er3+ ions

•Phosphate glasses doped with Er3+ ions and Au nanoparticles were synthesized.•TEM, optical absorption, and PL spectroscopy analysis were performed.•The influence of Au nanoparticles size on the emission of Er3+ ions was evaluated.•Enhancement of Er3+ photoluminescence in presence of small Au clusters is revealed.•Energy transfer from Au clusters to the excited states of Er3+ ions is presumed. Gold nanoparticles incorporated in glass medium are the object of keen interest due to their unique properties induced by plasmonic effects: coloration, noticeable optical nonlinearity and rare earth ions photoluminescence enhancement. In this work, we examine the structure and optical properties of potassium aluminophosphate glasses doped with Er3+ ions and Au under the heat treatment below and above glass transition temperature. The heat treatment of the glass at temperatures above Tg is shown to facilitate the formation of plasmonic gold nanoparticles and decrease near-infrared luminescence intensity of Er3+ ions. On the contrary, a similar treatment of the studied glasses at temperatures below Tg doesn't induce plasmonic absorption and leads to the intensity enhancement of Er3+ luminescence. Formation of gold clusters in the glass treated at lower temperatures is supposed to enable the energy transfer process between clusters and rare-earth ions which is expressed in luminescence intensity enhancement.