Synthesis and Characterization of K-Doped SiO₂ nanoparticles with blue persistent luminescence: A novel approach using the sol-gel method

While persistent luminescence (PersL) materials have many important applications and are actively being studied, blue-emitting phosphors propose the biggest challenges and lack of suitable materials. Among any solids that can serve as blue emitting PersL matrices, amorphous silicon dioxide (SiO₂) stands out with great chemical stability, high transparency, radiation resistance, and easly of adjusting the shape. We demonstrate a novel and environmentally friendly method for synthesising PersL SiO₂ nanoparticles doped with K ions. Optical and morphological properties of amorphous silica nanoparticles were studied in the course of slightly doping pure silica with K ions (0.1; 0.5; 1.0 and 1.5 at%). An intensive blue photoluminescence (PL) with a maximum of 465 nm (2.7 eV) and another band at 327 nm (3.8 eV) were detected for K-doped samples, which is not normally present for pure silica glass. The 0.1 and 0.5 at% K- K-doped samples exhibit blue persistent luminescence (PersL) that lasts up to a minute. Similar blue PL bands have been reported for porous silicas doped with Na and K ions, but no information about the nanoparticle's morphology and PL decay kinetics has been discovered. The temperature-dependent PL afterglow for 0.5 at% K-doped sample is observed to be slightly more intense at 100 K and 10 K compared to room temperature, suggesting its use at lower temperatures. Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) microanalysis confirmed the presence of K in amorphous silica. Increasing the K ion concentration leads to larger particle size and aggregation.