Tuning Molecular Afterglow via Rare‐Earth Complexation in Monodisperse SiO 2 Microparticles

Abstract 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 (RE 3+ ) complexation and incorporation into SiO 2 microparticles (MPs) under hydrothermal conditions, is presented. Doping 1,10‐phen into SiO 2 MPs activates phosphorescence at 488 nm, with a quantum yield of 2.59% and a lifetime of 1.14 s. Upon coordination with various RE 3+ ions (La 3 ⁺, Y 3 ⁺, Gd 3 ⁺, Lu 3 ⁺), both the quantum yield (3.00–9.02%) and afterglow lifetime (0.07–1.46 s) are finely tunable. Remarkably, Gd 3 ⁺, through its paramagnetic effect, enhances intersystem crossing more efficiently than the heavy‐atom effect of Lu 3 ⁺, resulting in a higher quantum yield but a shorter afterglow duration. In contrast, Y 3 ⁺, 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 RE 3+ complexation within SiO 2 matrices, offering promising potential for the development of advanced photonic crystal platforms in optoelectronic technologies.