Controlled synthesis of lanthanide-doped Gd₂O₂S nanocrystals with novel excitation-dependent multicolor emissions

Developing multicolor-emitting materials has significant value in many research fields such as displays, bioimaging, and information storage. The widely adopted strategies to realize multicolor emission are tuning the material composition, phase, and size. Herein, the emission color was continuously controlled from yellow to pink by simply changing the excitation wavelength from 254 nm to 365 nm for Tb³⁺/Eu³⁺ co-doped Gd₂O₂S NCs. The Gd₂O₂S NCs with different morphologies, including nanoplate with various sizes and flower-like, were successfully prepared by seed-mediated, Na⁺/Y³⁺ co-doped, and S concentration-tuned methods. The results indicated that Na⁺ ions greatly promote the growth of Gd₂O₂S NCs and Y³⁺ ions have an impact on their shape. Moreover, the PL intensity of the 2%Eu-doped flower-like Na/Y:Gd₂O₂S (F-NYG) NCs decreased by about 24.7%, 6.8%, and 5.1% under 254 nm, 316 nm, and 348 nm excitation, respectively; this is due to less non-radiative relaxation paths above the excited state of Eu³⁺:⁵D₀ at longer excitation wavelength, which result in a decreased degree of the PL intensity reduction.