Cryogenic enabled multicolor upconversion luminescence of KLa(MoO4)2:Yb3+/Ho3+ for dual-mode anti-counterfeiting

Current Developments in Emerging Lanthanide-Doped Persistent Luminescent Scintillators and Their Applications

Lanthanide-doped scintillators have the ability to convert the absorbed X-ray irradiation into ultraviolet (UV), visible (Vis), or near-infrared (NIR) light. Lanthanide-doped scintillators with excellent persistent luminescence (PersL) are emerging as a new class of PersL materials recently. They have attracted great attention due to their unique "self-luminescence" characteristic and potential applications. In this review, we comb through and focus on current developments of lanthanide-doped persistent luminescent scintillators (PersLSs), including their PersL mechanism, synthetic methods, tuning of PersL properties (e. g. emission wavelength, intensity, and duration time), as well as their promising applications (e. g. information storage, encryption, anti-counterfeiting, bio-imaging, and photodynamic therapy). We hope this review will provide valuable guidance for the future development of PersLSs.

Low-temperature in situ preparation of Eu3+/Tb3+-doped CaMoO4/SrMoO4 nanoparticle thin films and their application in anti-counterfeiting

Rare earth-doped metal oxide thin films exhibit remarkable potential for application in anti-counterfeiting, owing to their exceptional fluorescent properties. However, the existing fabrication techniques for these rare earth-doped luminescent thin films are predominantly complex and necessitate high-temperature conditions. In light of this issue, we present a low-temperature method for in situ fabrication of luminescent Ca1-xMoO4:Eux3+ and Sr1-xMoO4:Tbx3+ nanocrystal thin films by a solution deposition process. The developed method has the advantages of simple operation, rapid and low-temperature synthesis. The optimal chemical compositions of molybdate-based luminescent films are Ca0.90MoO4:Eu0.103+ and Sr0.90MoO4:Tb0.103+. Moreover, we evaluate the practical feasibility of luminescent nanoparticle films in the field of anti-counterfeiting by combining the unique fluorescent properties of rare earth ions and designing customized fluorescent patterns.

Improving upconversion luminescence intensity of BiTa7O19:Er3+/Yb3+ by polyvalent Sb co-doping

BiTa₇O₁₉:Er³⁺/Yb³⁺/Sb phosphors were successfully synthesized by high temperature solid sintering. X-ray diffraction (XRD), fluorescence spectrometry and X-ray photoelectron spectroscopy (XPS), were used to analyze the phase structure, upconversion luminescence (UCL) features and Sb valence state, respectively. The results suggest that polyvalent Sb with Sb³⁺ and Sb⁵⁺ can replace the Ta⁵⁺ sites in a BiTa₇O₁₉ host to form a pure phase. Compared with BiTa₇O₁₉:0.1Er³⁺/0.4Yb³⁺, polyvalent Sb doping further improves UCL intensity by 1.2 times under 980 nm laser stimulation with a powder density of 44.59 W cm^-2. This is due to the adjustment of the local lattice structure of BiTa₇O₁₉ by the polyvalent Sb. The maximum absolute sensitivity (S_A) and relative sensitivity (S_R) can be estimated from the UCL variable-temperature spectra as 0.0098 K^-1 at 356 K and 0.0078 K^-1 at 303 K using the luminescence intensity ratio (LIR) approach. The outcomes show that host local lattice adjustment using polyvalent elements is an effective way to improve luminescence intensity, and it is possible to use BiTa₇O₁₉:Er³⁺/Yb³⁺/Sb as a temperature sensor.

Lanthanide-doped Na2MgScF7 exhibiting downshifting and upconversion emissions for multicolor anti-counterfeiting

Na₂MgScF₇ (NMSF) was experimentally obtained for the first time by combining hydrothermal and high-temperature solid-state reactions. X-ray powder diffraction (XRD) combined with Rietveld refinement confirms that NMSF is crystallized in the space group Imma with the cell parameters a = 10.40860(18), b = 7.32804(12) and c = 7.52879(11) Å, α = β = γ = 90° and V = 574.256(24) ų. Through doping with Tb³⁺ or Eu³⁺ ions, downshifting yellow-green or red emission could be achieved in NMSF-based phosphors, respectively. Upconversion emission could also be designed by doping with Yb³⁺-Er³⁺, Yb³⁺-Tm³⁺, Yb³⁺-Ho³⁺ or Er³⁺. Moreover, the NMSF:Er³⁺ phosphor exhibited green upconversion emission upon excitation at 980 nm, and it exhibited red emission upon excitation at 1532 nm. Finally, recognizable patterns were obtained under excitation at 254, 365 and 980 nm, indicating that the as-prepared phosphors can be applied to multicolor anti-counterfeiting. Moreover, our synthesis strategy opens up new avenues for the synthesis of novel fluorides.

A multi-color persistent luminescent phosphor β-NaYF4:RE3+ (RE = Sm, Tb, Dy, Pr) for dynamic anti-counterfeiting

Conventional luminescent materials generally exhibit uni-color and transient emission under UV excitation, which makes them mediocre in the field of anti-counterfeiting. The high-level anti-counterfeiting techniques are always becoming more complicated and in need of multi-color and persistent luminescent materials. Herein, we report a series of β-NaYF₄:RE³⁺ (RE = Sm, Tb, Dy, Pr) persistent luminescent phosphors with multi-color emitting and ultra-long persistent luminescence under the irradiation of X-rays. The effects of doping concentrations of RE³⁺ on the size, morphology, radioluminescence and afterglow performance of the products are investigated in detail. Hexagonal structured rod-like β-NaYF₄:Tb³⁺ crystals show super strong X-ray response and the afterglow signal lasts for up to seven days after X-rays are turned off. Upon X-rays irradiation, some of the F⁻ ions are expected to escape from the crystal lattice by elastic collisions, leading to the generation of Frenkel defects: the F vacancies and interstitials , which capture electrons and release them slowly to achieve different afterglow emission times. Taking advantages of the extraordinary radioluminescence performance of the β-NaYF₄:RE³⁺ persistent luminescent phosphors, the dynamic anti-counterfeiting patterns that containing rich time-resolved information were successfully designed.

A dynamic anti-counterfeiting pattern was successfully designed by using the excellent luminescence characteristics of long afterglow materials under X-ray excitation.