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.

Study of a color-tunable long afterglow phosphor Gd1.5Y1.5Ga3Al2O12:Tb3+: luminescence properties and mechanism

Long afterglow phosphors play a significant role in practical applications. However, due to their complex electronic structures, it is difficult to obtain tunable long afterglow phosphors. Herein, a novel long afterglow phosphor, Gd_1.5Y_1.5Ga₃Al₂O₁₂:Tb³⁺, was successfully synthesized. Its detailed structural information was extracted via the Rietveld method, and its corresponding optical properties were further systematically explored via photoluminescence (PL), phosphorescence and thermoluminescence (TL) spectroscopy. Both the photoluminescence and long afterglow properties showed tunable behavior with a variation in the concentration of Tb³⁺. The investigation of the tunability of its photoluminescence and long afterglow properties revealed that the cross-relaxation energy transfer mechanism contributes to its tunable character. Meanwhile, long-lasting phosphorescence could be observed for a few hours by the naked eye in a dark environment after discontinuing the UV irradiation. Due to the potential existence of the photo-excited (Tb³⁺)⁺, the defect clusters were proposed, with oxygen vacancies acting as electron trapping centers and (Tb³⁺)⁺ attracting holes. Finally, an appropriate mechanism for the tunable long afterglow emission was proposed.

Long afterglow phosphors play a significant role in practical applications.

La2O2CO3:Tb3+ one-dimensional nanorod with green persistent luminescence

Trivalent terbium-doped oxycarbonate (La₂O₂CO₃:1%Tb³⁺) one-dimensional nanorods are synthesized via a facile precipitation method. The average length of La₂O₂CO₃:1%Tb³⁺ nanorods is 184.5 nm. Doping Tb³⁺ ions led to several visible emission peaks at 486 nm, 542 nm, and 587 nm under excitation of 258 nm wavelength light. The green afterglow at 542 nm can be detected almost 600 s after ceasing the UV-light irradiation. It can be calculated that the La₂O₂CO₃:1%Tb³⁺ sample has one shallow trap depth (E = 0.848 eV) by measuring the thermoluminescence. All the results indicate that a simple precipitation method can synthesize a one-dimensional nanorod with green persistent luminescence.

Trivalent terbium-doped oxycarbonate (La₂O₂CO₃:1%Tb³⁺) one-dimensional nanorods are synthesized via a facile precipitation method.

High-Sensitivity and Wide-Linear-Range Thermoluminescence Dosimeter LiMgPO4:Tm,Tb,B for Detecting High-Dose Radiation

High-sensitivity and wide-linear-range thermoluminescence dosimeter (TLD) is of importance for detecting high-dose radiation in industry, medicine, and agriculture as well as materials and food processing. In this work, we synthesize a series of LiMgPO₄ doped with Tm³⁺, Tb³⁺, and B³⁺ via a high-temperature solid-state reaction technique. To observe the effect of dopants, we first investigate the structure by Rietveld refinement of high-quality X-ray diffraction (XRD) data and then study the thermoluminescence (TL) properties of samples radiated by β-rays in detail. The TL signal of LiMgPO₄:Tm,Tb,B is originated from Tm³⁺ 4f-4f transitions. The kinetic parameters are obtained through fitting the TL glow curve based on the general-order kinetics model, revealing that the dominant TL peak at ∼323 °C is related to ∼1.49 eV trap. Through constructing the vacuum-referred binding energy (VRBE) scheme, we uncover that this deep trap mainly originates from the Tb³⁺ dopant acted as the captured center of free hole. After codoping 0.6% B³⁺, the sensitivity of sample as TLD increases ∼170%. According to the radiation dose-dependent TL intensities, the sensitivity of LiMgPO₄:Tm,Tb,B is about 200% larger than that of the commercial LiF:Mg,Cu,P at 0.08 Gy, and more sensitive at higher dose. Moreover, the studied sample has wider linear range (up to 10 000 Gy) toward high-dose side, good reproducibility (RSD ∼ 4.6%), and weak fading (∼8% after 34 days), and therefore has potential application as TLD for monitoring high-dose radiation.

Efficient X-ray excited short-wavelength infrared phosphor

X-ray combined with short-wavelength infrared (SWIR) phosphors, that can make full advantage of the deeper tissue penetration of SWIR light, can be used as a fluorescent probe to realize biological imaging of deep tissues; they are, however, limited by their lower luminescence efficiency. Here, we describe a strategy to synthesize highly efficient SWIR luminescence phosphor based on the efficient energy transfer process between charge transfer state (CTS) of Yb³⁺ and the ⁶I_J levels of Gd³⁺ as well as Gd³⁺-Gd³⁺. This allows us to achieve 813.8 mW/m² of SWIR luminescence power in Yb³⁺-BaGd_0.6Y_0.4ZnO₅ (BGYZ). Our results highlight that this approach to enhance SWIR luminescence may provide new opportunities for the deep-tissue biological imaging.