Multi-responsive deep-ultraviolet emission in praseodymium-doped phosphors for microbial sterilization

Pr3+ Visible to Ultraviolet Upconversion for Antimicrobial Applications

This paper addresses the upconversion of blue light to ultraviolet-C (UVC) with Pr3+-activated materials for antibacterial applications of UVC. It discusses the processes through which UV radiation provides biocidal effects on microorganisms, along with the most popular UVC sources employed in these processes. We describe the electronic and optical properties of the Pr3+ ion, emphasizing the conditions the host material must meet to obtain broad and intense emission in the UVC from parity-allowed transitions from the 4f5d levels and provide a list of materials that fulfill these conditions. This paper also delineates lanthanide-based upconversion, focusing on Pr3+ blue to UVC upconversion via the 3P0 and 1D2 intermediate states, and suggests routes for improving the quantum efficiency of the process. We review literature related to the use of upconversion materials in antimicrobial photodynamic treatments and for the blue to UVC upconversion germicidal effects. Further, we propose the spectral overlap between the UVC emission of Pr3+ materials and the germicidal effectiveness curve as a criterion for assessing the potential of these materials in antimicrobial applications. Finally, this paper briefly assesses the toxicity of materials commonly used in the preparation of upconversion materials.

Force-Induced Ultraviolet C Luminescence of Pr3+-Doped Sr2P2O7 for X-Ray Dosimetry

Mechanoluminescent materials have broad application prospects in advanced displays, stress imaging, and anti-counterfeiting owing to their ability to convert mechanical stimuli into light. However, most previous studies have focused on the visible and near-infrared regions. Although natural ultraviolet C (UVC) light is nearly absent on the Earth's surface, it plays an important role in many fields. Therefore, the development of smart materials capable of emitting UVC mechanoluminescence (ML) and expanding the application scenarios of UVC ML are significant but challenging. Here the ML property of Sr2P2O7:Pr3+ is examined, which stems from the 5d→4f transition of Pr3+ and is located over the UVC region. The peak wavelength of the UVC ML of Sr2P2O7:Pr3+ is ≈230 nm, which is, to the best of this knowledge, the shortest ML wavelength reported to date. It is further demonstrated that the UVC ML of Sr2P2O7:Pr3+ is associated with trapped charge carriers and can be conveniently regulated by adjusting the X-ray excitation time. Relying on this unique characteristic, the potential of the UVC ML of Sr2P2O7:Pr3+ as an indicator of the X-ray radiation dose is demonstrated. This study enriches the family of mechanoluminescent materials and expands the available wavelength of ML to the UVC region.

Upconversion Phosphor-Driven Photodegradation of Plastics

Plastic waste poses a profound threat to ecosystems and human health, necessitating novel strategies for effective degradation in nature. Here, we present a novel approach utilizing upconversion phosphors as additives to significantly accelerate plastic photodegradation in nature via enhancing ultraviolet (UV) radiation. Pr-doped Li2CaGeO4 (LCGO:Pr) upconversion phosphors readily converting blue light into deep-UV radiation, dramatically improve photodegradation rates for polyethylene (PE) and polyethylene terephthalate (PET) microplastics. In situ spectroscopic studies show that upconversion fluorescence initiates the photophysical cleavage of C-C and C-O bonds in the backbones of PE and PET, resulting in plastic degradation. Moreover, incorporating LCGO:Pr into polypropylene (PP) sheets realizes markedly enhanced photodamage, with the cracking area increasing by nearly 38-fold under simulated sunlight for 10 days. This underscores the potential of employing this approach for the construction of light-driven destructible polymers. Further optimization and exploration of material compatibility hold promise for developing sustainable photodegradable plastics.

Optically driven ultraviolet-C glowing from an in situ trapping-detrapping approach

In recent years, the world has witnessed rapid progress in research on ultraviolet luminescent materials, ranging from high-level anticounterfeiting and solar-blind optical tagging to antibacterial applications. In particular, a background-signal free solar-blind surveillance of ultraviolet-C photons provides an opportunity in bright indoor and outdoor environments. However, ambient daylight or inevitable external photostimulation is always eliminated or underestimated in the research of persistent phosphors. Herein, an in situ trapping-detrapping experimental procedure is employed to reveal more information on the total trap energy and trap modulations after photostimulation. Our findings reveal the presence of optically active trapping defects with photostimulated detrapping and retrapping behavior. This work provides a fundamental advance in revealing the trap distribution and trap reshuffling during glowing-in-the-daylight events, offering what we believe to be new insights into manipulating traps.

Pushing Trap-Controlled Persistent Luminescence Materials toward Multi-Responsive Smart Platforms: Recent Advances, Mechanism, and Frontier Applications

Smart stimuli-responsive persistent luminescence materials, combining the various advantages and frontier applications prospects, have gained booming progress in recent years. The trap-controlled property and energy storage capability to respond to external multi-stimulations through diverse luminescence pathways make them attractive in emerging multi-responsive smart platforms. This review aims at the recent advances in trap-controlled luminescence materials for advanced multi-stimuli-responsive smart platforms. The design principles, luminescence mechanisms, and representative stimulations, i.e., thermo-, photo-, mechano-, and X-rays responsiveness, are comprehensively summarized. Various emerging multi-responsive hybrid systems containing trap-controlled luminescence materials are highlighted. Specifically, temperature dependent trapping and de-trapping performance is discussed, from extreme-low temperature to ultra-high temperature conditions. Emerging applications and future perspectives are briefly presented. It is hoped that this review would provide new insights and guidelines for the rational design and performance manipulation of multi-responsive materials for advanced smart platforms.

Manipulation of Multimodal and Multicolor Luminescence via Interplay of Traps and Rare Earth Emission Centers in Calcium Tungstate

Multimodal luminescence involves color-tunable and wavelength manageable photon emissions upon variable luminescence pathways in response to different external stimuli, which provides clear visualization and high-level confidentiality for information encryption technologies. Integrating multimodal luminescence into a single matrix is regarded as a feasible strategy but remains a big challenge. In this work, multimodal (photoluminescence, persistent luminescence, upconversion luminescence, and thermally stimulated luminescence) and multicolor luminescence (green, yellow, orange, pink to red) is achieved in CaWO4:Yb3+,Er3+,Eu3+ phosphor by employing an interplay of traps and rare earth emission centers. Bright emission in a wide color gamut is achieved dynamically in response to thermal disturbance and light illumination, which further allows for on-demand emission manipulation in space and time dimensions. The compatible coexistence of multiple rare earth emissive centers together with abundant photoactive traps contributes to the excellent integration of multimodal photon emissions in calcium tungstate. This work provides a good example of integrating multimodal luminescence into one single matrix and indicates potential in advanced high-level information encryption applications.

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.

Energy-Trapping Management in X-Ray Storage Phosphors for Flexible 3D Imaging

X-ray imaging has received sustained attention for healthcare diagnostics and nondestructive inspection. To develop photonic materials with tunable photophysical properties in principle accelerates radiation detection technologies. Here the rational design and synthesis of doped halide perovskite CsCdCl₃ :Mn²⁺ , R⁴⁺ (R = Ti, Zr, Hf, and Sn) are reported as next generation X-ray storage phosphors, and the capability is greatly improved by trap management via Mn²⁺ site occupation manipulation and heterovalent substitution. Specially, CsCdCl₃ :Mn²⁺ , Zr⁴⁺ displays zero-thermal-quenching (TQ) radioluminescence and anti-TQ X-ray-activated persistent luminescence even up to 448 K, further revealing the charge-carrier compensation and redeployment mechanisms. X-ray imaging with the resolution of 12.5 lp mm^-1 is demonstrated, and convenient 3D X-ray imaging for the curved objects is realized in a time-lapse manner. This work demonstrates efficient modulation of energy traps to achieve high storage capacities and promote future research into flexible X-ray detectors.

Shortwave Ultraviolet Persistent Luminescence of Sr2MgSi2O7: Pr3

Currently, extensive research activities are devoted to developing persistent phosphors which extend beyond the visible range. In some emerging applications, long-lasting emission of high-energy photons is required; however, suitable materials for the shortwave ultraviolet (UV-C) band are extremely limited. This study reports a novel Sr₂MgSi₂O₇ phosphor doped with Pr³⁺ ions, which exhibits UV-C persistent luminescence with maximum intensity at 243 nm. The solubility of Pr³⁺ in the matrix is analysed by X-ray diffraction (XRD) and optimal activator concentration is determined. Optical and structural properties are characterised by photoluminescence (PL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) spectroscopy techniques. The obtained results expand the class of UV-C persistent phosphors and provide novel insights into the mechanisms of persistent luminescence.

Multimodal and Multicolor Anti-counterfeiting Realized in CaCd2Ga2Ge3O12 with a Single Activator of Mn2

The continuously growing significance of information security and authentication has put forward many new requirements and challenges for modern luminescent materials and anti-counterfeiting technologies. Recently, luminescent materials have attracted much attention in this field owing to their legibility, repeatability, multicolor, and multiple stimuli-responsive nature. In this work, the efficient multicolor and multimodal luminescence material CaCd₂Ga₂Ge₃O₁₂:Mn²⁺ was successfully designed and synthesized using the strategy of single-doped Mn²⁺ in a single matrix. Also, we combined the morphology, crystal structure, energy band calculation, luminescence properties, and trap analysis to study the optical data storage capacity of CaCd₂Ga₂Ge₃O₁₂:Mn²⁺. Interestingly, in the presence of the 254 nm UV lamp, the sample can exhibit a tunable emission color from bule to cyan to yellow by increasing the dopant concentration of Mn²⁺. Also, under the afterglow and thermoluminescence luminescence modes, it presented strong yellow emission centered at 558 nm. Based on the advantage of multiple tunable luminescence, samples were made into anti-counterfeiting ink and were used to print four optical devices through the screen printing technology. The results show that the material has excellent multicolor anti-counterfeiting properties under the three luminescence modes, which has contributed to the development of many kinds of luminescent anti-counterfeiting materials for security purposes.

UV-A,B,C Emitting Persistent Luminescent Materials

The nearly dormant field of persistent luminescence has gained fresh impetus after the discovery of strontium aluminate persistent luminescence phosphor in 1996. Several efforts have been put in to prepare efficient, long decay, persistent luminescent materials which can be used for different applications. The most explored among all are the materials which emit in the visible wavelength region, 400-650 nm, of the electromagnetic spectrum. However, since 2014, the wavelength range is extended further above 650 nm for biological applications due to easily distinguishable signal between luminescent probe and the auto-fluorescence. Recently, UV-emitting persistent materials have gained interest among researchers' due to their possible application in information storage, phototherapy and photocatalysis. In the present review, we summarize these recent developments on the UV-emitting persistent luminescent materials to motivate young minds working in the field of luminescent materials.

Interplay of defect levels and rare earth emission centers in multimode luminescent phosphors

Multimode luminescence generally involves tunable photon emissions in response to various excitation or stimuli channels, which demonstrates high coding capacity and confidentiality abilities for anti-counterfeiting and encryption technologies. Integrating multimode luminescence into a single stable material is a promising strategy but remains a challenge. Here, we realize distinct long persistent luminescence, short-lived down/upconversion emissions in NaGdTi₂O₆:Pr³⁺, Er³⁺ phosphor by emloying interplay of defect levels and rare earth emission centers. The materials show intense colorful luminescence statically and dynamically, which responds to a wide spectrum ranging from X-ray to sunlight, thermal disturbance, and mechanical force, further allowing the emission colors manipulable in space and time dimensions. Experimental and theoretical approaches reveal that the Pr³⁺ ↔ Pr⁴⁺ valence change, oxygen vacancies and anti-site Ti_Gd defects in this disordered structure contributes to the multimode luminescence. We present a facile and nondestructive demo whose emission color and fade intensity can be controlled via external manipulation, indicating promise in high-capacity information encryption applications.

Multichannel Control of PersL/Upconversion/Down-Shifting Luminescence in a Single Core-Shell Nanoparticle for Information Encryption

Persistent luminescence (PersL) has been attracting substantial attention in diverse frontier applications such as optical information security and in vivo bioimaging. However, most of the reported PersL emissions are based on the dopants instead of the host matrix, which also plays an important role. In addition, there are few works on the PersL-based multifunctional nanoplatform in nanosized materials. Here, we report a class of novel nanostructure designs with PersL, upconversion, and down-shifting luminescence to realize the fine-tuning of emission colors under different excitation modes including steady-state irradiation, time-gating, and PersL generation. Blue, orange, and green emissions were easily achieved in such a single nanoparticle under suitable excitation modes. Moreover, the physical origin of the PersL of the CaF₂ matrix was discussed by simulating the energy band structure with Ca_xF_y defects. Our results provide new opportunities for the design of a new class of multifunctional materials, showing great promise in the field of information encryption security and multilevel anticounterfeiting.

Bright UV-C Phosphors with Excellent Thermal Stability-Y1-xScxPO4 Solid Solutions

The structural and luminescence properties of undoped Y_1-xSc_xPO₄ solid solutions have been studied. An intense thermally stable emission with fast decay (τ_1/e ~ 10^-7 s) and a band position varying from 5.21 to 5.94 eV depending on the Sc/Y ratio is detected and ascribed to the 2p O-3d Sc self-trapped excitons. The quantum yield of the UV-C emission, also depending on the Sc/Y ratio, reaches 34% for the solid solution with x = 0.5 at 300 K. It is shown by a combined analysis of theoretical and experimental data that the formation of Sc clusters occurs in the solid solutions studied. The clusters facilitate the creation of energy wells at the conduction band bottom, which enables deep localization of electronic excitations and the creation of luminescence centers characterized by high quantum yield and thermal stability of the UV-C emission.

Visible-to-ultraviolet-C upconverted photon for multifunction via Ca2SiO4:Pr3

The ultraviolet C (UVC) photon plays a key role in a broad spectrum of fields. With the implementation of the Minamata Convention, searching for a new way to achieve UVC light is highly desired. Here we develop a material of Ca₂SiO₄:Pr³⁺ that can emit UVC light upon excitation of a 450-nm laser or even a very cheap 450-nm LED, a fact confirmed by using a solar blind camera to capture UVC emission from Ca₂SiO₄:Pr³⁺. In addition, smart anti-counterfeiting and inactivation of Bacillus subtilis applications using Ca₂SiO₄:Pr³⁺ are also confirmed.