Photoluminescence imaging of Eu(III) and Tb(III)-embedded SiO₂ nanostructures

We prepared SiO₂ embedded with Eu(III) and Tb(III) by a modified Stöber method. The nanostructures were highly thermal stable and showed a significant enhancement in photoluminescence after thermal annealing at above 600 °C. Emissions by indirect charge transfer excitation were much stronger than those in response to a direct excitation transition. 2D and 3D-photoluminescence image profiles were fully examined, and the emissions of Eu(III) observed between 570 and 720 nm and Tb(III) between 450 and 700 nm were attributed to the ⁵D₀→⁷F_J (J=0,1,2,3,4) and ⁵D₄→⁷F_J (J=6,5,4,3) transitions, respectively. The Eu(III) and Tb(III) appeared to be embedded at sites with lower symmetry without an inversion center. In the SiO₂ matrix, the oxidation states of Eu(III) and Tb(III) showed no change, even after thermal annealing. The present study describes an effective methodology for developing efficient light emitting materials using an activator ion-embedded silica structure. - Highlights: • SiO₂ nanostructures were embedded with Eu(III) and Tb(III) ions. • Photoluminescence imaging profiles were fully characterized. • The nanostructures were highly stable and showed strong red and green emissions. • Eu(III)/SiO₂ and Tb(III)/SiO₂ showed 28× and 66× stronger PL after thermal annealing