A strategy to enhance the up-conversion luminescence of nanospherical, rod-like and tube-like NaYF4: Yb3+, Er3+ (Tm3+) by combining with carbon dots

Up-conversion luminescence materials, such as NaYF4: Yb3+, Er3+ (Tm3+), have very promising application prospects in the biomedical field and have attracted continuous interest in recent years. However, their low up-conversion luminescence performance is still one of the key obstacles to their application. Herein, we have developed a simple and environment-friendly strategy to enhance the up-conversion luminescence of NaYF4: Yb3+, Er3+ (Tm3+) by combining carbon dots (CDs), which were obtained using a wheat straw as the starting material. This luminescence enhancement strategy was effective for different doping ions (NaYF4: Yb3+, Er3+ and NaYF4: Yb3+, Tm3+), different phase structures (cubic and hexagonal) and different morphologies (nanosphere, rod-like, and tube-like). The emission intensities at 539 nm increased around 322 times for tube-like CD@NaYF4: Yb3+, Er3+, 63 times for rod-like CD@NaYF4: Yb3+, Er3+, and 20 times for nanospherical CD@NaYF4: Yb3+, Er3+ compared with that of NaYF4: Yb3+, Er3+ without CDs. The mechanism of luminescence enhancement is probably due to the decrease in defects and the electron capture by CDs and transfer to the lower energy levels of Er3+ or Tm3+ ions.

Automated summary

A strategy utilizing carbon dots obtained from wheat straw has been developed to enhance the up-conversion luminescence of NaYF4: Yb3+, Er3+ (Tm3+), showing significant improvement in emission intensity for different structures and morphologies of samples. The mechanism of luminescence enhancement is likely attributed to the reduction in defects and electron capture by the carbon dots, leading to transfer to lower energy levels of Er3+ or Tm3+ ions.