LiAl5O8:Fe3+ and LiAl5O8:Fe3+, Nd3+ as a New Luminescent Nanothermometer Operating in 1st Biological Optical Window

Fe3+-activated magnetoplumbite persistent luminescence phosphor by modulating the oxygen vacancy

Broadband near-infrared (NIR) spectroscopy has gained significant attention due to its versatile application in various fields. In the realm of NIR phosphors, Fe3+ ion is an excellent activator known for its nontoxic and harmless nature. In this study, we prepared an Fe3+-activated SrGa12O19 (SGO) NIR phosphor and analyzed its phase and luminescence properties. Upon excitation at 326 nm, the SGO:Fe3+ phosphor exhibited a broadband emission in the range 700-1000 nm, peaking at 816 nm. The optical band gap of SGO:Fe3+ was evaluated. To enhance the long-lasting phosphorescence, an oxygen vacancy-rich SGO:Fe3+ (VO-SGO:Fe3+) sample was prepared for activation. Interestingly, the increase in the oxygen-vacancy concentration indeed contributed to the activation of persistent luminescence of Fe3+ ions. The VO-SGO:Fe3+ sample has a long duration and high charge storage capacity, allowing it to perform efficiently in various applications. This work provides the foundation for further design of Cr3+-free PersL phosphors with efficient NIR PersL.

Tetracoordinate Fe3+ Activated Li2ZnAO4 (A = Si, Ge) Near-Infrared Luminescent Phosphors

Fe3+-doped near-infrared (NIR) phosphors have received a lot of interest because they are nontoxic, inexpensive, and ecologically benign. In this work, Fe3+-activated Li2ZnAO4 (A = Si, Ge) phosphors were synthesized by solid-phase reactions, in which Fe3+ entered the Zn2+ tetrahedral site. When excited by 300 nm UV light, broad NIR emission bands at 750 nm (Li2ZnSiO4: Fe3+) and 777 nm (Li2ZnGeO4: Fe3+) were observed, with internal quantum efficiencies (IQE) of 62.70% (Li2ZnSiO4: Fe3+) and 30.57% (Li2ZnGeO4: Fe3+). The thermal stability was increased from 35.43 to 49.79% at 373 K via cationic regulation. The combination of activation energy, electron-phonon coupling, and Debye temperature explained the improved thermal stability of Li2ZnGeO4: Fe3+ phosphor. Besides, the as-synthesized phosphor demonstrated sensitive and selective Cu2+ ion detection.

High-Pressure Near-Infrared Luminescence Studies of Fe3+-Activated LiGaO2

A 0.25% iron (Fe3+)-doped LiGaO2 phosphor was synthesized by a high-temperature solid-state reaction method. The phosphor was characterized utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM), high-pressure photoluminescence, and photoluminescence decay measurement techniques using diamond anvil cells (DACs). The powder X-ray analysis shows that the phosphor is a β polymorph of LiGaO2 with an orthorhombic crystallographic structure at room temperature. The SEM result also confirms the presence of well-dispersed micro-rod-like structures throughout the sample. The photoluminescence studies in the near-infrared (NIR) range were performed at ambient, low-temperature, and high-pressure conditions. The synthesized phosphor exhibits a photoluminescence band around 746 nm related to the 4T1 → 6A1 transition with a 28% quantum efficiency at ambient conditions, which shifts toward longer wavelengths with the increase of pressure. The excitation spectra of Fe3+ are very well fitted with the Tanabe-Sugano crystal-field theory. The phosphor luminescence decays with a millisecond lifetime. The high-pressure application transforms the β polymorph of LiGaO2 into a trigonal α structure at the pressure of about 3 GPa. Further increase of pressure quenches the Fe3+ luminescence due to the amorphization process of the material. The prepared phosphor exhibits also mechanoluminescence properties in the NIR spectral region.

Research Progress and Development of Near-Infrared Phosphors

Near-infrared (NIR) light has attracted considerable attention in diverse applications, such as food testing, security monitoring, and modern agriculture. Herein, the advanced applications of NIR light, as well as various devices to realize NIR light, have been described. Among the diverse NIR light source devices, the NIR phosphor-converted light-emitting diode (pc-LED), serving as a new-generation NIR light source, has obtained attention due to its wavelength-tunable behavior and low-cost. As one of the key materials of the NIR pc-LED, a series of NIR phosphors have been summarized depending on the type of luminescence center. Meanwhile, the characteristic transitions and luminescence properties of the above phosphors are illustrated in detail. In addition, the status quo of NIR pc-LEDs, as well as the potential problems and future developments of NIR phosphors and applications have also been discussed.

Environmentally friendly Fe3+-activated near-infrared-emitting phosphors for spectroscopic analysis

Highly efficient Fe³⁺-activated Sr_2-yCa_y(InSb)_1-zSn_2zO₆ broadband near-infrared-emitting phosphors with tunable emission from 885 to 1005 nm are developed as alternative for primarily studed toxic Cr³⁺-activated near-infrared-emitting phosphors for application in spectroscopy analysis.

NIR luminescence lifetime nanothermometry based on phonon assisted Yb3+-Nd3+ energy transfer

Luminescence thermometry in biomedical sciences is a highly desirable, but also highly challenging and demanding technology. Numerous artifacts have been found during steady-state spectroscopy temperature quantification, such as ratiometric spectroscopy. Oppositely, the luminescence lifetime is considered as the most reliable indicator of temperature thermometry because this luminescent feature is not susceptible to sample properties or luminescence reabsorption by the nanothermometers themselves. Unfortunately, this type of thermometer is much less studied and known. Here, the thermometric properties of Yb3+ ions in Nd0.5RE0.4Yb0.1PO4 luminescent temperature probes were evaluated, aiming to design and optimize luminescence lifetime based nanothermometers. Temperature dependence of the luminescence lifetimes is induced by thermally activated phonon assisted energy transfer from the 2F5/2 state of Yb3+ ions to the 4F3/2 state of Nd3+ ions, which in turn is responsible for the significant quenching of the Yb3+:2F5/2 lifetime. It was also found that the thermal quenching and thus the relative sensitivity of the luminescent thermometer can be intentionally altered by the RE ions used (RE = Y, Lu, La, and Gd). The highest relative sensitivity was found to be S R = 1.22% K-1 at 355 K for Nd0.5Y0.4Yb0.1PO4 and it remains above 1% K-1 up to 500 K. The high sensitivity and reliable thermometric performance of Nd0.5La0.4Yb0.1PO4 were confirmed by the high reproducibility of the temperature readout and the temperature uncertainty being as low as δT = 0.05 K at 383 K.