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.