Improvement of luminescence properties of Eu-doped ZnO nanoparticles followed by their incorporation into a silica aerogel matrix

Silica-based composite materials are of great importance due to the high porosity and large specific surface area of silica (SiO₂) glass that help to explore several applications. This research reports the physical properties of SiO₂/Eu%-Zn₂SiO₄ composites (Eu% = 0.1, 0.5, and 1%) prepared by a modified sol-gel process. First, structural, morphological, and vibrational analysis show distinct fine diffraction peaks of Eu-ZnO crystallized in hexagonal symmetry. The incorporation of this latter in the SiO₂ matrix followed by thermal treatment up to 1200 °C in ambient conditions serves to obtain the zinc silicate phase (Zn₂SiO₄). X-ray diffraction (XRD) and infrared characterization techniques demonstrate the establishment of a mixed structure composed of SiO₂ and Zn₂SiO₄ phases. In addition, the morphology of the samples shows that zinc silicate grains are well surrounded by a silica shell matrix. Such microstructure is directly related to the utilized homemade sol-gel-based protocol. Moreover, photoluminescence analysis proves the difficulty of europium incorporation into the ZnO phase. Instead, the zinc silicate matrix is more tolerant to such a procedure. However, the resolution of the emission peaks and the emitted light are getting much better. Several europium emission bands are reported, which are attributed to the well-known 4f-4f transitions. In addition, Europium helps to activate some deep defects in the Zn₂SiO₄ crystal material that improve the performance of the optical thermometer sensor. A high relative sensitivity value of 2.36%/K is obtained in the cryogenic operating temperature range of [12–140 K]. The findings of the study prove the huge potential of lanthanide-based zinc silicate phosphor for optical thermometry applications.