Chromium Ion Pairs Induce Highly Efficient and Thermostable Broadband NIR Phosphor for Plant Lighting and Night Vision
Chen Zhou, Junxi Wang, Pingzhi Zhang, Chengzhu Tang, Xuan Shi, Siying Li, Huanhuan Chen, Мaxim S. Моlokeev, Andrey Zolotov, Wei Li, Wai‐Yeung Wong, Zhi Zhou, Mao Xia
Abstract
Near-infrared (NIR) light has a high application value in various fields due to its spectral characteristics. Typically, the broadband NIR emission of Cr 3+ is based on the transition of 4 T 2 → 4 A 2, while the 2 E level emits narrowband emission. This work discovered broadband NIR emission from the [ 4 A 2, 4 T 2 ] coupling excited state energy level in the spinel structure. The dense and adjacent Al1O 6 as the occupied sites of Cr 3+ provides a structural basis for the exchange coupling effect under high Cr 3+ concentration, as confirmed by the analysis of site occupancy, formation energy, bond valence sum, and effective coordination number. Spectral information and EPR signals indicate that the [ 4 A 2, 4 T 2 ] coupling excited state in the emission spectrum corresponds to the downward shift of the T 2 energy level caused by the Cr 3+ –Cr 3+ exchange coupling interaction in the strong crystal field of LAO:Cr 3+ . The internal and external quantum efficiencies of LAO:0.15Cr 3+ are 80.6% and 30.3%, respectively. The luminescence intensity at 370 and 423 K is approximately 92% and 85% respectively of that at room temperature. The excellent luminescence thermal stability is attributed to the activation energy of 0.21 eV and the Huang–Rhys factor S = 3.95. Finally, the material was fabricated into pc-LEDs and its applications in night vision and plant lighting were explored.