Pulsed-Laser-Induced Simple Synthetic Route for Tb₃Al₅O₁₂:Ce³⁺ Colloidal Nanocrystals and Their Luminescent Properties

Cerium-doped Tb₃Al₅O₁₂ (TAG:Ce³⁺) colloidal nanocrystals were synthesized by pulsed laser ablation (PLA) in de-ionized water and lauryl dimethylaminoacetic acid betain (LDA) aqueous solution for luminescent bio-labeling application. The influence of LDA molecules on the crystallinity, crystal morphology, crystallite size, and luminescent properties of the prepared TAG:Ce³⁺ colloidal nanocrystals was investigated in detail. When the LDA solution was used, smaller average crystallite size, narrower size distribution, and enhanced luminescence were observed. These characteristics were explained by the effective role of occupying the oxygen defects on the surface of TAG:Ce³⁺ colloidal nanocrystal because the amphoteric LDA molecules were attached by positively charged TAG:Ce³⁺ colloidal nanocrystals. The blue-shifted phenomena found in luminescent spectra of the TAG:Ce³⁺ colloidal nanocrystals could not be explained by previous crystal field theory. We discuss the 5d energy level of Ce³⁺ with decreased crystal size with a phenomenological model that explains the relationship between bond distance with 5d energy level of Ce³⁺ based on the concept of crystal field theory modified by covalency contribution.