Excitation-Power-Dependent Upconversion Luminescence Competition in Single β-NaYbF4:Er Microcrystal Pumped at 808 nm

Abstract

Controlling the upconversion luminescence (UCL) intensity ratio, especially pumped at 808 nm, is of fundamental importance in biological applications due to the water molecules exhibiting low absorption at this excitation wavelength. In this work, a series of β-NaYbF4:Er microrods were synthesized by a simple one-pot hydrothermal method and their intense green (545 nm) and red (650 nm) UCL were experimentally investigated based on the single-particle level under the excitation of 808 nm continuous-wave (CW) laser. Interestingly, the competition between the green and red UCL can be observed in highly Yb3+-doped microcrystals as the excitation intensity gradually increases, which leads to the UCL color changing from green to orange. However, the microcrystals doped with low Yb3+ concentration keep green color which is independent of the excitation power. Further investigations demonstrate that the cross-relaxation (CR) processes between Yb3+ and Er3+ ions result in the UCL competition. Graphical Abstract

Multiwavelength Responsive Luminescence for Temperature Sensing and Visualized Information Encoding/Decoding Based on Er3+/Tb3+-Doped Ba2Ga2GeO7 Phosphors

“… , The optimum concentration of doping ions is determined to be 8%, which is similar to the luminescence behavior excited by 382 nm. Figure d shows the UC emission spectra excited by a 980 nm laser, and the green emission bands located at ∼525 and ∼548 nm can be attributed to 2 H 11/2 , 4 S 3/2 → 4 I 15/2 , while the red emission peaks at 650, 656, 667, 671, and 677 nm are due to the transitions from several sublevels of Stark splitting of 4 F 9/2 to the 4 I 15/2 level under the crystal field, − and the optimal doping concentration of Er 3+ in terms of UC emission is 10%. It is worth mentioning that the red emission is extremely weak compared with green one upon 382 and 808 nm excitations, and this phenomenon is independent of the Er 3+ doping concentration.…”