Crystalline phase effect on the up-conversion processes and white emission of Yb³⁺/Er³⁺/Tm³⁺:Y₂Si₂O₇ nanocrystals

Yb³⁺,Er³⁺,Tm³⁺:Y₂Si₂O₇ nanopowders were fabricated by a sol-gel method and then annealed at two different temperatures of 1050 °C and 1480 °C for 12 h to investigate the phase effect on the structural and optical properties. X-ray diffraction patterns (XRD) of all powders revealed that most of the peaks were in good harmony with the standard JCPDS cards of Y₂Si₂O₇ (PDF #38-0223 and PDF #38-0440). SEM images of the powders were taken to examine the morphology and chemical composition of the powders. Diffuse reflection spectra of Y₂Si₂O₇ exhibited varying number of transitions depending on the dopant ion in all powders in the range of 400-1050 nm. The spectral properties of the powders were investigated to identify the possible up-conversion (UC) emission mechanism in the range between 400 and 900 nm under 975 nm excitation. A broadening white light emission was observed with increasing laser pumping power at room temperature as well. Spectral profiles of the transitions observed in both reflectance and up-conversion luminescence spectra were found to be crystalline phase dependent.