Tuning Molecular Afterglow via Rare-Earth Complexation in Monodisperse SiO₂ Microparticles

Rational control of triplet-state emissions in organic molecules is key to advancing organic phosphors for optoelectronic applications. However, achieving precise modulation of both afterglow intensity and lifetime remains challenging. Here, a tunable afterglow system based on 1,10-phenanthroline (1,10-phen), enabled by rare-earth (RE³⁺) complexation and incorporation into SiO₂ microparticles (MPs) under hydrothermal conditions, is presented. Doping 1,10-phen into SiO₂ MPs activates phosphorescence at 488 nm, with a quantum yield of 2.59% and a lifetime of 1.14 s. Upon coordination with various RE³⁺ ions (La³⁺, Y³⁺, Gd³⁺, Lu³⁺), both the quantum yield (3.00-9.02%) and afterglow lifetime (0.07-1.46 s) are finely tunable. Remarkably, Gd³⁺, through its paramagnetic effect, enhances intersystem crossing more efficiently than the heavy-atom effect of Lu³⁺, resulting in a higher quantum yield but a shorter afterglow duration. In contrast, Y³⁺, which lacks a heavy-atom effect, increases the rigidity of the 1,10-phen framework, thereby improving the phosphorescence quantum yield to 3.11% and extending the afterglow lifetime to 1.46 s. These findings highlight a versatile and effective strategy for tuning the optical properties of organic molecules via RE³⁺ complexation within SiO₂ matrices, offering promising potential for the development of advanced photonic crystal platforms in optoelectronic technologies.