Power-tunable multicolor upconversion in nanocrystals under single-wavelength excitation

Area of Science:

• Materials Science
• Nanotechnology
• Photonics

Background:

• Upconversion luminescence enables generating higher energy photons from lower energy excitation.
• Controlling emission color in upconversion materials often requires multiple excitation wavelengths or complex material compositions.

Purpose of the Study:

• To demonstrate tunable upconversion luminescence in three primary colors (green, red, blue) using a single excitation wavelength (980 nm) by varying excitation intensity.
• To explore the photon-order-dependent upconversion processes responsible for color tuning.

Main Methods:

• Synthesis of core/shell/shell nanocrystals (approx. 50 nm diameter) with specific dopant concentrations (Er3+, Yb3+, Tm3+) in distinct layers.
• Utilizing a single 980 nm continuous-wave (CW) laser source to excite the nanocrystals.
• Modulating the excitation power density to control the upconversion emission color.

Main Results:

• Achieved tunable emission from green to red to blue by systematically increasing the 980 nm laser power density.
• Correlated color shifts with 2-photon (green), 3-photon (red), and 4-photon (blue) upconversion processes.
• Validated dynamic color modulation through chromaticity coordinate shifts on the CIE diagram.

Conclusions:

• Demonstrated a simplified, single-wavelength excitation method for achieving full RGB color tunability in upconversion luminescence.
• The rationally designed nanocrystal architecture enables precise control over emission pathways via excitation intensity.
• Paved the way for advancements in photonics, high-resolution color displays, and biomedical applications.