Nd³⁺-Sensitized multicolor upconversion luminescence from a sandwiched core/shell/shell nanostructure.

Area of Science:

• Materials Science
• Nanotechnology
• Biomedical Engineering

Background:

• Lanthanide-doped upconversion nanoparticles (UCNPs) are valuable for bioimaging, biosensing, and therapeutics.
• Multicolor upconversion luminescence (UCL) is typically achieved using near-infrared excitation at ~980 nm.
• This ~980 nm excitation overlaps with water absorption, causing significant biological heating, limiting in vivo applications.

Purpose of the Study:

• To develop multicolor UCNPs with efficient upconversion luminescence (UCL) at ~800 nm.
• To overcome the biological heating problem associated with traditional ~980 nm excitation.
• To demonstrate tailored multicolor emission from blue to white for multiplexed biological applications.

Main Methods:

• Synthesized a sandwich-structure core/shell/shell UCNP (NaYbF4:Tm,Nd@CaF2:Nd@CaF2:Yb,Er).
• Incorporated substantial Nd3+ sensitizers in the middle shell for efficient light harvesting.
• Utilized bidirectional excitation energy migration to activate Tm (blue) and Er (green/red) emissions.

Main Results:

• Achieved multicolor UCL from UCNPs excited at ~800 nm, avoiding water absorption and local heating.
• Demonstrated efficient excitation harvesting by Nd3+ sensitizers in the middle shell.
• Controlled lanthanide ion content to tune emission colors from blue to white.

Conclusions:

• Nd3+-sensitized UCNPs provide a solution to the heating problem in biological applications.
• Tailored multicolor emission enables diverse multiplexed bioimaging and sensing strategies.
• These UCNPs offer a promising platform for advanced biomedical applications without thermal complications.