All reactants and solvents were used as received without further purification. Dimethyldiethoxysilane (DEDMS, 98%), zirconium isopropoxide (Zr(OPri)4), titanium isopropoxide (Ti(OPri)4), tantalum ethoxide (Ta(OEt)5) and niobium ethoxide (Nb(OEt)5) were purchased from Sigma-Aldrich. Ethanol and cyclohexane were obtained from Scharlab.
In a typical synthesis, 0.250 mL of the UCNP suspension in cyclohexane was added to a pre-hydrolyzed DEDMS solution (DEDMS : H2O : EtOH in a 1 : 1 : 1 molar ratio, acidified with HCl at pH = 1, and 30 minutes of hydrolysis). Then, an appropriate amount of the metal alkoxide (M = Ta, Nb, Ti and Zr) was added. The M : Si molar ratio was fixed at 1 : 4. After 30 minutes of stirring, the sol was sonicated for 5 minutes.
For the preparation of monoliths, 2.2 mL of sol was poured into polyethylene round vials (Kartell) and left to dry at 308 K for one week. The final monoliths were cylinders of about 20 mm diameter and 1.5 mm high.
Thin films of around 450 nm thickness were prepared by spin coating on a glass substrate. The nanocomposite made of PDMS–MxOy containing Yb3+/Er3+- or Yb3+/Tm3+-doped UCNPs are referred to in the manuscript as HyTa, HyNb, HyTi and HyZr, followed by the active ions (Yb3+/Er3+ or Yb3+/Er3+).
In a typical synthesis, 0.250 mL of the UCNP suspension in cyclohexane was added to a pre-hydrolyzed DEDMS solution (DEDMS : H2O : EtOH in a 1 : 1 : 1 molar ratio, acidified with HCl at pH = 1, and 30 minutes of hydrolysis). Then, an appropriate amount of the metal alkoxide (M = Ta, Nb, Ti and Zr) was added. The M : Si molar ratio was fixed at 1 : 4. After 30 minutes of stirring, the sol was sonicated for 5 minutes.
For the preparation of monoliths, 2.2 mL of sol was poured into polyethylene round vials (Kartell) and left to dry at 308 K for one week. The final monoliths were cylinders of about 20 mm diameter and 1.5 mm high.
Thin films of around 450 nm thickness were prepared by spin coating on a glass substrate. The nanocomposite made of PDMS–MxOy containing Yb3+/Er3+- or Yb3+/Tm3+-doped UCNPs are referred to in the manuscript as HyTa, HyNb, HyTi and HyZr, followed by the active ions (Yb3+/Er3+ or Yb3+/Er3+).