• Organic–inorganic hybrid composites;
  • Sol–gel processes;
  • Luminescence;
  • Quantum yield


Transparent monoliths of urea cross-linked tripodal siloxane-based hybrids, named tri-ureasils, were prepared by the sol–gel process, using a wide concentration range of hydrochloric acid catalyst (1.0 × 10–3 ≤ [HCl] ≤ 2.0 M). The gelation time of the monoliths was controlled by varying the amount of water (2.2 and 22.2 mmol) and HCl (between 4.0 × 10–5 and 8.0 × 10–2 mmol) incorporated. Their local structure was characterized by X-ray diffraction, 29Si and 13C nuclear magnetic resonance, mid-infrared and ultraviolet/visible absorption spectroscopy, and photoluminescence in steady-state and time resolved modes. The effect of [HCl] in the enhancement of the emission quantum yield was quantified. Although all the hybrids display emission at room temperature in the blue spectral region, it was observed that maximum and constant quantum yield values of 0.13 ± 0.01 are achieved for 0.01 ≤ [HCl] ≤ 0.1 M.