Preparation and characterization of blue-light-excited nanophosphors using an economically low-energy process

• Three microwave (MW) processes achieved high PL efficiency of nanophosphor.
• The EG solvent provided homogeneous nucleation and activator homogenization.
• Pseudo-oxide crystal may form during microwave heating in EG + KOH system.
• Low MW power 100 W economically reduced post-heating temperature to 600 °C.
• Residual hydroxyl/carbonyl groups on nanophosphors may be as chemical grafting.

Spherical and red nanophosphors of Y2O3:Eu3+ are prepared using urea hydrolysis that needs a long coprecipitation time (>4 h) and post-annealing at 800 °C for 2 h. Three microwave (MW) processing routes of MW-urea hydrolysis, MW-urea-EG solvolysis, and MW-urea-EG + KOH solvolysis were used to achieve short processing time and low energy consumption, thus obtaining high photoluminescence (PL) efficiency. The organic ethylene glycol (EG) solvent could prevent the nanoparticle surface from developing defects and provide a high-temperature bath for homogeneous nucleation and activator homogenization through rapid microwave volume heating. The 611 nm red emission of MW-urea-EG + KOH-derived phosphors excited by 466 nm was higher than that of the MW-urea-EG-derived phosphors after post-heat treatment at 600 °C. The pre-crystallized structure may have formed during microwave heating in EG + KOH system, but the amorphous structure formed in the EG system. The low power (100 W for 3.5 min) of the MW-urea-EG + KOH process economically reduced the post-heating temperature to 600 °C, and maintained the nano-size of phosphors with a high PL intensity. The residual hydroxyl and carbonyl groups on the obtained nanophosphors may be beneficial to be as chemical grafting in subsequent paste/slurry regulation for various LED and FPD applications.