A and B sites dual substitution by Na+ and Cu2+ co-doping in CsPbBr3 quantum dots to achieve bright and stable blue light emitting diodes.

Light-emitting perovskite quantum dots (PeQDs) are extensively investigated owing to their evident merits. However, it is still a challenge to adjust their intrinsic emissions and enhance their thermal stability to achieve full-color highly emissive QD-based light-emitting diodes (QLEDs), especially blue QLEDs. Herein, we demonstrate an effective strategy to fundamentally stabilize the crystal structure of CsPbBr3 QDs by codoping Na+ and Cu2+ ions, which are designed to substitute Cs+ (A sites) and Pb2+ (B sites), respectively. It is found out that the codoping metal ions have significantly improved the thermal stability and the optical properties of the QDs. 40% of the emission intensity can be remained after 8 thermal cycles (20-120 °C) for CsPbBr3: Na+/Cu2+ QDs, whilst less than 10% is maintained for undoped CsPbBr3 QDs. Accordingly, stable blue QLEDs are packed by CsPbBr3: Na+/Cu2+ QDs. Strong electroluminescence with the maximum luminance of 7161 cd m-2 and low turn-on voltage of 2.4 V are realized. The CIE coordinates are tuned from green (0.10, 0.74) to blue (0.17, 0.25) via Na+ and Cu2+ codoping. The maximum external quantum efficiency (EQEmax) is obtained as 4.52% for PeLEDs based on codoped QDs. The proposed metal ions A and B sites dual substitution strategy guarantees PeQDs as an extremely promising prospect in potential applications as high-resolution displays and high-quality lightings.

Strategy for optical thermometry based on temperature-dependent charge transfer to the Eu3+ 4f-4f excitation intensity ratio in Sr3Lu(VO4)3:Eu3+ and CaWO4:Nd3.

Optical thermometry has been developed as a promising temperature-sensing technique. We propose a new, to the best of our knowledge, strategy of fluorescence intensity ratio (FIR), based on an abnormal thermal quenching effect. In the phosphors of Sr3Lu(VO4)3:Eu3+ and CaWO4:Nd3+, the f-f emission intensity of the doped lanthanide ions increases with raising temperature upon the excitation of the charge transfer band (CTB) of the host. The abnormal thermal quenching is caused by the thermally activated absorption, which is proved by temperature-dependent diffuse reflectance spectra. The opposite change tendency of M-O (M=V5+ or W6+) CTB and Ln3+ (Ln=Eu3+ or Nd3+) f-f transitions has been observed in the temperature-dependent excitation spectra and employed as the thermometric probe in ratiometric luminescent thermometry. The strategy applies to the FIR technique in lanthanide singly doped phosphors and eliminates the limitation of thermal-coupled levels. It opens up new possibilities of ratiometric optical thermometry. In addition, the derived maximum relative sensitivity is larger than the value obtained via thermal-coupled levels in the same sample. This illustrates that optical thermometry based on abnormal thermal quenching might be a feasible and effective method.