Tailored molecular engineering of mesoporous silica for high concentration Er doping and unconventional 1640 nm luminescence

Abstract

The incorporation of high concentrations of erbium (Er) into mesoporous silica is crucial for advancing applications in up-conversion lasers, optical amplifiers, biomedical diagnostics, and light detection and ranging (LiDAR) technologies. This study presents a novel fabrication strategy to achieve Er doping levels up to 6.7 wt% within mesoporous KIT-6 silica by functionalizing the matrix with 1,2-phthaloyl diamido-propyltriethoxysilane (1,2-PA-APTS), followed by solid-phase batch extraction and annealing at 1000 °C. Comprehensive characterization using XRD, BET, FE-SEM, HRTEM, XPS, EPMA, UV-vis, and photoluminescence (PL) spectroscopy was carried out to ensure the material formation and structure–property correlation. A well-ordered 3D mesoporous silica (KIT-6) was synthesized with a high surface area of 1410 m² g⁻¹ and a pore size of 3.5 nm. Er oxide nanoparticles formed in two size regimes (∼3.5 nm and ∼18 nm) and were homogeneously distributed within the matrix, minimizing clustering. PL spectra revealed prominent emission peaks at 1539 nm and an enhanced, unconventional emission at 1640 nm. The formation of ordered Er oxide nanoparticles (Er₂O₃) within the crystalline silica matrix, coupled with enhanced Er concentration, was the dominant factor contributing to the sharp absorption and broad photoluminescence emission. The unconventional emission at 1640 nm is attributed to Stark splitting of Er³⁺ energy levels. This approach effectively addresses dopant clustering challenges at high concentrations and provides a scalable method for controlled rare-earth incorporation into mesoporous silica, advancing its potential for diverse photonic applications.