Understanding and Effective Tuning of Red‐to‐Green Upconversion Emission in Ho‐Based Halide Double Perovskite Microcrystals

Abstract

Ho‐based lead‐free double perovskite microcrystals (MCs), Cs2NaHo1‐xYbxCl6, are synthesized and demonstrated to be promising optical temperature sensing materials by understanding the concentration‐dependent upconversion (UC) luminescence mechanisms. By optimizing the dopant concentration, a dominant emission shifting from red to green is successfully achieved in an activator‐rich system. During this process, the red to green emission intensity ratio (R/G) can be changed from 12.5 (pure red light) to 0.14 (pure green light). It is clarified that the cross‐relaxation (CR) process between activator and the energy transfer process between Yb3+ and Ho3+ are the key mechanisms of UC luminescence intensity and R/G ratio variation. Moreover, the intensity of red and green UC emission shows strong dependence on temperature, resulting from the competition between CR and energy transfer in the emission levels. The high‐sensitivity Ho‐based thermometer can be obtained by Cs2NaHo0.99Yb0.01Cl6 MCs with bright red UC luminescence, whose fluorescence intensity ratio thermometer gains maximum relative sensitivities reaching 0.68% K−1 at 400 K. The multicolor UC luminescence quantitative modeling mentioned here is crucial for understanding the concentration‐dependence UC luminescence characteristics and to optimize the design of the Ho‐based thermometer. This study can be an extension of the application range for perovskite UC materials.

Temperature-dependent self-trapped models regulating energy transfer in rare earth double perovskites via 5s2 electron doping

“…17–22 Rare earth ions typically exhibit a wide emission range from ultraviolet (UV) to infrared due to their rich (4f n ) electronic configurations, along with long PL lifetimes and excellent optical stability. 23–26 Xia's group reported on Bi 3+ :Cs 2 Ag(In 1− x Tb x )Cl 6 halide perovskites, 27 which modulated luminescence from green to orange. However, the tuning range of luminescence did not extend to cover the entire spectrum.…”

A Strategy for Rapid Synthesis of Carbon Nanodots with Reversible Photoluminescence Switching for Sensitive Dynamic Anti‐Counterfeiting

“…Generally, the luminescent materials include organic dyes, [ 16 ] perovskites, [ 17 ] semiconductor quantum dots (SQDs), [ 18 ] metal ligands, [ 19 ] and carbon nanodots (CDs). [ 20–22 ] Among them, traditional organic dyes suffer from photobleaching, perovskites present poor environmental stability, SQDs are enriched with toxic heavy metal elements (Cd, Pd), and metal ligands are complicated in process and other defects.…”