Cr³⁺-Doped NIR Phosphor with Well-Defined Stokes/Anti-Stokes Phonon Sidebands for a Ratiometric Thermometer and Thermally Stable NIR LEDs

Abstract

Near-infrared (NIR) luminescent materials have attracted enormous attention for the cutting-edge applications in optical thermometer and NIR LEDs. Herein, we report a highly efficient Cr3+-doped NIR phosphor, BaAl4Sb2O12:0.024Cr3+ (BASO:Cr3+), with 91% internal quantum efficiency. Strikingly, BASO:Cr3+ possesses rare and typical Stokes/anti-Stokes phonon sidebands. The Stokes phonon sideband decreases with increasing temperature, while the anti-Stokes one increases considerably. Consequently, this inverse change has gifted the BASO:Cr3+ with excellent thermal stability, which maintains 118% of the room temperature emission intensity at 423 K. In addition, the well-defined Stokes/anti-Stokes phonon sidebands are applied to a ratiometric thermometer with a maximum relative sensitivity factor of 3.12% K–1 at 150 K. Finally, a well-performing NIR LED is made with BASO:Cr3+, which can be used for nondestructive testing, information encryption, and night vision. Our findings not only shed light on the emission behavior of Cr3+ but also point out an avenue for thermally stable NIR phosphors and a sensitive optical thermometer.

Host Dependency of Boundary between Strong and Weak Crystal Field Strength of Cr3+ Luminescence

“…The investigation into solid-state luminescence is currently undergoing a surge in the advancement of near-infrared (NIR) luminescence emanating from Cr 3+ doped inorganic phosphors. − These phosphors exhibit absorption in the blue spectral light region, rendering them excitable by high efficiency blue GaN chips. The emitted NIR light has been extensively applied in diverse fields, such as bioimaging, horticulture, night vision, nondestructive food testing, and temperature sensing, owing to its imperceptibility to the human eye and its profound penetration depth into biological tissues. Chemists and spectroscopists display heightened interest in the bell-shaped emission band comprising a broad array of continuous NIR wavelengths, as opposed to the sharp-line emissions typically observed in lanthanide ion doped phosphors. − The luminescence behaviors of Cr 3+ can be comprehended through the utilization of the Tanabe–Sugano (T-S) diagram, which elucidates the correlations between the energy levels of Cr 3+ and the crystal-field strength. , This diagram employs the crystal-field strength parameter, Dq, and the Racah parameters B and C. Herein, we are concerned with multiplet term levels and not the detailed crystal-field split energy levels.…”

“…1−3 These phosphors exhibit absorption in the blue spectral light region, rendering them excitable by high efficiency blue GaN chips. The emitted NIR light has been extensively applied in diverse fields, such as bioimaging, 4 horticulture, 5 night vision, 6 nondestructive food testing, 7 and temperature sensing, 8 owing to its imperceptibility to the human eye and its profound penetration depth into biological tissues. Chemists and spectroscopists display heightened interest in the bell-shaped emission band comprising a broad array of continuous NIR wavelengths, as opposed to the sharpline emissions typically observed in lanthanide ion doped phosphors.…”

Crystal-field regulation enables broadband-to-line emission switching in Cr3+-activated pyroxenes

“…As a unique luminescence activator, transition metal (TM) ions Cr 3+ -doped deep-red and near-infrared (NIR) phosphors have received much attention in recent years due to their high performance. 1–4 In general, Cr 3+ ions strongly prefer to occupy the octahedral sites in the crystal lattice. 5 The photoluminescence (PL) properties of Cr 3+ -activated materials are determined by the energy of the excited state levels 2 E and 4 T 2 and the ground state level 4 A 2 , which are strongly dependent on the crystal field strength of the host lattice.…”

Sensitive Luminescence Thermometry through Excitation Intensity Ratio in Eu-Doped BaTiO3

“…Research on optical thermometry has been rapidly multiplying during the past decade due to the promising characteristics of noninvasive probing, adaptable working temperature range, and biocompatibility. − Lanthanide or transition metal ion-doped luminescent materials are major candidates for temperature-related applications such as cellular thermal sensing, thermal imaging, ,, and cryogenic/high-temperature detection by offering various temperature readout methods. , Changes in the peak position/shape, emission/excitation intensity, decay lifetime, and anisotropy have been harnessed as thermometric parameters, providing different schemes of optical thermometry. ,− Among various operation schemes, luminescence intensity ratio (LIR) thermometry currently dominates this field due to its merits of simplicity, diversity, precision, and low cost . Generally, this method requires a pair of emission peaks at distinct wavelengths for a self-referenced temperature readout.…”