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 degrees 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.