Synergy between structural rigidity and cluster defects in a bright near-infrared Cr3+-based phosphor for excellent thermal stability and long afterglow

Abstract

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) driven by blue LEDs have emerged as promising future NIR light sources with high energy efficiency and compact structure for applications in medical diagnosis, night vision, and agriculture. However, development of thermally robust NIR light sources presents a great challenge. Herein, we report a blue light-pumped Y₃Al₂Ga₃O₁₂:Cr³⁺ phosphor with thermally stable broadband NIR emission (105% at 423 K) and a high quantum efficiency of 76%, covering the range from 630 to 950 nm. Moreover, the Y₃Al₂Ga₃O₁₂:Cr³⁺ phosphor displayed long persistent luminescence (PersL) under UV charging. Synchrotron based extended X-ray absorption fine structure (EXAFS) indicated the octahedral Cr³⁺ lattice sites and local structure. Low temperature-dependent EXAFS studies revealed rigid octahedral coordination of Cr³⁺ ions at Al/GaO₆ sites with minimal thermally activated distortion even in the second/third coordination shell. The lattice stiffness resulted in superior temperature-dependent NIR photoluminescence properties (80 to 433 K) with abnormal anti-thermal quenching desirable for pc-LEDs at 150 °C. Furthermore, the intrinsic defects were probed using positron annihilation lifetime spectroscopy and density functional theory, which suggested feasible formation of oxygen vacancies (V_O) and cluster defects (V_Al/Ga–V_O). Introduction of abundant traps with wide-ranging trap depths (∼0.7 to 1 eV) facilitated the long PersL with UV charging and defect activated thermal stability. Finally, the fabricated NIR pc-LED device exhibits efficient electroluminescence and its potential applications in imaging and night vision were demonstrated. Then, promising long PersL of the fabricated thin film under X-ray charging is presented. This work investigates the application prospects and highlights the important structural and defect related dynamics of this promising phosphor for NIR pc-LED devices.