Up-Conversion Emissions Characteristics of Non-Aqueous Sol–Gel Derived RE₃Al₅O₁₂ Nanocrystals

The RE₃Al₅O₁₂ (REAG:Er₃Al₅O₁₂, Er:Y₃Al₅O₁₂ and Er:Yb₃Al₅O₁₂) up-conversion (UC) nanocrystals have been prepared by the non-aqueous sol–gel method. The green and red UC emissions are attributed to the ²H₁₁/₂, ⁴S₃/₂ → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺, respectively, were obtained for all samples with a 975 nm semiconductor LD excitation. For Er₃Al₅O₁₂ nanocrystals, the green and red UC emissions have similar intensities. Y and Yb ions have no evident effect on the peak positions, but strongly affected the intensities of the green and red UC emissions of the Er. A much higher intensity of the green relative to red UC emission was observed for Er:Y₃Al₅O₁₂ nanocrystals, however, the red UC emission became predominant for Er:Yb₃Al₅O₁₂ nanocrystals. It was suggested that the two-photon process was responsible for the green and red UC emissions mechanism for all the samples.