Mn5+-activated Ca6Ba(PO4)4O near-infrared phosphor and its application in luminescence thermometry

Ultrasensitive Colorimetric Luminescence Thermometry by Progressive Phase Transition

Luminescent materials that display quick spectral responses to thermal stimuli have attracted pervasive attention in sensing technologies. Herein, a programmable luminescence color switching in lanthanide-doped LiYO2 under thermal stimuli, based on deliberate control of the monoclinic (β) to tetragonal (α) phase transition in the crystal lattice, is reported. Specifically, a lanthanide-doping (Ln3+ ) approach to fine-tune the phase-transition temperature in a wide range from 294 to 359 K is developed. Accordingly, an array of Ln3+ -doped LiYO2 crystals that exhibit progressive phase transition, and thus sequential color switching at gradually increasing temperatures, is constructed. The tunable optical response to thermal stimuli is harnessed for colorimetric temperature indication and quantitative detection, demonstrating superior sensitivity and temperature resolution (Sr = 26.1% K-1 , δT = 0.008 K). The advances in controlling the phase-transition behavior of luminescent materials also offer exciting opportunities for high-performance personalized health monitoring.

Valence conversion and site reconstruction in near-infrared-emitting chromium-activated garnet for simultaneous enhancement of quantum efficiency and thermal stability

Achievement of high photoluminescence quantum efficiency and thermal stability is challenging for near-infrared (NIR)-emitting phosphors. Here, we designed a "kill two birds with one stone" strategy to simultaneously improve quantum efficiency and thermal stability of the NIR-emitting Ca3Y2-2x(ZnZr)xGe3O12:Cr garnet system by chemical unit cosubstitution, and revealed universal structure-property relationship and the luminescence optimization mechanism. The cosubstitution of [Zn2+-Zr4+] for [Y3+-Y3+] played a critical role as reductant to promote the valence transformation from Cr4+ to Cr3+, resulting from the reconstruction of octahedral sites for Cr3+. The introduction of [Zn2+-Zr4+] unit also contributed to a rigid crystal structure. These two aspects together realized the high internal quantum efficiency of 96% and excellent thermal stability of 89%@423 K. Moreover, information encryption with "burning after reading" was achieved based on different chemical resistance of the phosphors to acid. The developed NIR-emitting phosphor-converted light-emitting diode demonstrated promising applications in bio-tissue imaging and night vision. This work provides a new perspective for developing high-performance NIR-emitting phosphor materials.

Excited-State Dopant-Host Energy-Level Alignment: Toward a Better Understanding of the Photoluminescence Behaviors of Doped Phosphors

Luminescent materials, also known as phosphors, have been widely used for applications such as emissive displays, fluorescent lamps, light-emitting diodes, and X-ray scintillation detectors. The energy-level diagram of a phosphor is extremely important for understanding its photoluminescence behavior. Here, we demonstrate through a combined density functional theory and experimental study that excited-state energy-level alignment accounts for the photoluminescence behaviors much better than ground-state energy-level alignment. An efficient doped phosphor should exhibit a type I excited-state dopant-host energy-level alignment, regardless of whether its ground-state alignment is type I. A type II excited-state dopant-host energy-level alignment implies that exciton dissociation, resulting in photoluminescence quenching. Our results provide not only a better understanding of the photoluminescence behaviors of the reported phosphors but also critical guidance for designing prospective luminescent materials.

Shell Engineering on Thermal Sensitivity of Lifetime-Based NIR Nanothermometers for Accurate Temperature Measurement in Murine Internal Liver Organ

Lifetime-based NIR luminescent nanothermometry is ideally suited for temperature detection in living cells and in vivo, but the thermal sensitivity (S_r) modulation remains elusive. Herein, a thorough investigation is performed to unveil the shell effect on lifetime-based S_r by finely controlling the shell thickness of lanthanide-doped core-shell-shell nanoparticles. Owing to the space-dependent energy transfer and back energy transfer between Nd³⁺ and Yb³⁺ as well as the energy migration to surface quenchers, both active and inert shells can regulate the thermal-dependent nonradiative decays and NIR luminescence lifetime of Yb³⁺, which in turn modulates the S_r from 0.56% to 1.54% °C^-1. After poly(acrylic acid) modification of the optimal architecture, the tiny nanoprobes possess robust stability to fluctuations in the microenvironment, which enables accurate temperature mapping of inflammation in the internal liver organ of living mouse. This work will provide new insights for optimizing S_r and guidance for precise temperature measurements in vivo.

Comparison of Performance between Single- and Multiparameter Luminescence Thermometry Methods Based on the Mn5+ Near-Infrared Emission

Herein, we investigate the performance of single- and multiparametric luminescence thermometry founded on the temperature-dependent spectral features of Ca₆BaP₄O₁₇:Mn⁵⁺ near-infrared emission. The material was prepared by a conventional steady-state synthesis, and its photoluminescence emission was measured from 7500 to 10,000 cm^-1 over the 293-373 K temperature range in 5 K increments. The spectra are composed of the emissions from ¹E → ³A₂ and ³T₂ → ³A₂ electronic transitions and Stokes and anti-Stokes vibronic sidebands at 320 cm^-1 and 800 cm^-1 from the maximum of ¹E → ³A₂ emission. Upon temperature increase, the ³T₂ and Stokes bands gained in intensity while the maximum of ¹E emission band is redshifted. We introduced the procedure for the linearization and feature scaling of input variables for linear multiparametric regression. Then, we experimentally determined accuracies and precisions of the luminescence thermometry based on luminescence intensity ratios between emissions from the ¹E and ³T₂ states, between Stokes and anti-Stokes emission sidebands, and at the ¹E energy maximum. The multiparametric luminescence thermometry involving the same spectral features showed similar performance, comparable to the best single-parameter thermometry.

Enhanced Photoluminescence of Gd3Al4GaO12: Cr3+ by Energy Transfers from Co-Doped Dy3

LEDs for plant lighting have attracted wide attention and phosphors with good stability and deep-red emission are urgently needed. Novel Cr3+ and Dy3+ co-doped Gd3Al4GaO12 garnet (GAGG) phosphors were successfully prepared through a conventional solid-state reaction. Using blue LEDs, a broadband deep-red emission at 650−850 nm was obtained due to the Cr3+ 4T2 → 4A2 transition. When the Cr3+ concentration was fixed to 0.1 mol, the crystal structure did not change with an increase in the Dy3+ doping concentration. The luminous intensity of the optimized GAGG:0.1Cr3+, 0.01Dy3+ was 1.4 times that of the single-doped GAGG:0.1Cr3+. Due to the energy transfer from Dy3+ to Cr3+, the internal quantum efficiency reached 86.7%. The energy transfer from Dy3+ to Cr3+ can be demonstrated through luminescence spectra and fluorescence decay. The excellent properties of the synthesized phosphor indicate promising applications in the agricultural industry.