Multimodal Luminescence Research Articles

Multimode Luminescence Tailoring and Improvement of Cs2NaHoCl6 Cryolite Crystals via Sb3+/Yb3+ Alloying for Versatile Photoelectric Applications

AbstractLead‐free halide double perovskites are currently gaining significant attention owing to their exceptional environmental friendliness, structural adjustability as well as self‐trapped exciton emission. However, stable and efficient double perovskite with multimode luminescence and tunable spectra are still urgently needed for multifunctional photoelectric application. Herein, holmium based cryolite materials (Cs2NaHoCl6) with anti‐thermal quenching and multimode photoluminescence were successfully synthesized. By the further alloying of Sb3+ (s‐p transitions) and Yb3+ (f‐f transitions) ions, its luminescence properties can be well modulated, originating from tailoring band gap structure and enriching electron transition channels. Upon Sb3+ substitution in Cs2NaHoCl6, additional absorption peaking at 334 nm results in the tremendous increase of photoluminescence quantum yield (PLQY). Meanwhile, not only the typical NIR emission around 980 nm of Ho3+ is enhanced, but also the red and NIR emissions show a diverse range of anti‐thermal quenching photoluminescence behaviors. Furthermore, through designing Yb3+ doping, the up‐conversion photoluminescence can be triggered by changing excitation laser power density (yellow‐to‐orange) and Yb3+ doping concentration (red‐to‐green). Through a combined experimental‐theoretical approach, the related luminescence mechanism is revealed. In general, by alloying Sb3+/Yb3+ in Cs2NaHoCl6, abundant energy level ladders are constructed and more luminescence modes are derived, demonstrating great potential in multifunctional photoelectric applications.

Versatile and High‐Performance LiTaO3:Tb3+, Gd3+ Perovskite for Multimode Anti‐counterfeiting, Flexible X‐Ray Imaging, Continuous Stress Sensing, and Non‐Real‐Time Recording

AbstractMultimode luminescence relates to how charge carriers are transported and recombined in response to various physical excitations. It shows promising applications in many fields like advanced anti‐counterfeiting, information storage and encryption. Enabling a stable single compound with multimode luminescence is a unique technology but still remains a challenge. Herein, a versatile and high‐performance energy storage LiTaO3:0.01Tb3+,xGd3+ perovskite is discovered by utilizing the interplay of electron‐trapping defect levels and hole‐trapping Tb3+. It combines an excellent charge carrier storage capacity (≈7 and 12 times higher than state‐of‐the‐art BaFBr(I):Eu2+ and Al2O3:C), >1200 h storage duration, >40 h afterglow, efficient optically stimulated luminescence, persistent mechanoluminescence, and force‐induced charge carrier storage features. Particularly, it well responds to various stimuli channels, i.e., wide‐range X‐rays to 850 nm infrared photons, thermal activation, mechanical force grinding, or compression. To elucidate this multimode luminescence, charge carrier trapping and release processes in LiTaO3:0.01Tb3+,xGd3+ with various physical stimulations will be unraveled by combining the vacuum‐referred binding diagram construction, spectroscopy, thermoluminescence, and mechanoluminescence techniques. The versatile and high‐performance LiTaO3:0.01Tb3+,xGd3+ enables promising proof‐of‐concept multimode luminescence applications in advanced anti‐counterfeiting, flexible X‐ray imaging, continuous compression force sensing, and non‐real‐time recording.

Multimode-Responsive Luminescence of Er3+ Single-Activated CaF2 Phosphor for Advanced Information Encryption.

The current optical anticounterfeit strategies that rely on multimode luminescence in response to the photon or thermal stimuli have significant importance in the field of anticounterfeiting and information encryption. However, the dependence on light and heat sources might limit their flexibility in practical applications. In this work, Er3+ single-doped CaF2 phosphors that show multistimuli-responsive luminescence have been successfully prepared. The as-obtained CaF2:Er3+ phosphor exhibits green photoluminescence (PL) and color-tunable up-conversation (UC) luminescence from red to green due to the cross-relaxation of Er3+ ions. Additionally, as-obtained CaF2:Er3+ phosphors also display green mechano-luminescence behavior, which is induced by the contact electrification between the CaF2 particles and PDMS polymers, enabling the phosphor to flexibly respond to mechanical stimuli. Moreover, feasible anticounterfeiting schemes with the capability of multistimuli-responsive and flexible decryption have been constructed, further expanding the application of optical materials in the field of advanced anticounterfeiting and information encryption.

Quantum dots luminescent compounds with multimodal luminescence for fuel labeling

The article considers the possibility of labelling oil products using luminescent ‘fingerprints’ based on several types of quantum dots to protect fuel from falsification. For the synthesis of quantum dots, a scalable universal method was proposed using an available large-producible solvent and a stabilizer, oleic acid. Using the developed technique, quantum dots were obtained that luminescence in the entire visible range of the electromagnetic radiation spectrum. The formation of nanoparticles was confirmed by a set of instrumental research methods. The determination of the presence of quantum dots in the composition of an oil product was proposed using spectrofluorometry with no additional separation or dialization of nanoparticles from the sample. Using normal regular gasoline as an example, the effect of fuel on the luminescence of quantum dots and their aggregation was studied. The interaction of different types of quantum dots in the composition of the indicator and their influence on each other’s luminescence in solvent and gasoline were analyzed. The minimum detectable by the spectrofluorometric method concentrations of quantum dots in normal gasoline and the optimal proportions of quantum dots of various types in mixtures were determined.

Simultaneously Achieving Multicolor Emission of Down‐Shifting and Up‐Conversion in Yb3+, Er3+ ‐Codoped Cs2NaGdCl6 Double Perovskites

AbstractUltraviolet (UV) excited down‐shifting (DS) double perovskites with broad emission have potential applications in anti‐counterfeiting. However, discovering new materials and achieving multimode luminescence present significant challenges. In this work, a novel double perovskite, Cs2NaGdCl6 is synthesized, with sky‐blue self‐trapped exciton (STE) emission under UV excitation using a solvothermal method. By incorporating Er3+ ions into Cs2NaGdCl6, green DS and green up‐conversion (UC) luminescence are achieved under UV and near‐infrared (NIR) excitation. The addition of the sensitizer Yb3+ ion led to a significant enhancement of 21.5‐fold in DS red luminescence and 7.5‐fold in UC green luminescence. The color of both DS and UC luminescence in Cs2NaGdCl6:Yb3+, Er3+ is further adjusted from green‐dominated to red‐dominated, due to the cross‐relaxation process between Er3+ and Yb3+, Er3+ and Er3+, respectively. The combination of UC and DS luminescence, along with the ability to modulate emission color in rare‐earth‐based materials, opens new possibilities for high security anti‐counterfeiting applications.

General Synthesis of Carbon Dot-Based Composites with Triple-Mode Luminescence Properties and High Stability.

Carbon dot (CD)-based luminescent materials have attracted great attention in optical anti-counterfeiting due to their excellent photophysical properties in response to ultraviolet-to-visible excitation. Hence, there is an urgent need for the general synthesis of CD-based materials with multimode luminescence properties and high stability; however, their synthesis remains a formidable challenge. Herein, CDs were incorporated into a Yb,Tm-doped YF3 matrix to prepare CDs@YF3:Yb,Tm composites. The YF3 plays a dual role, not only serving as a host for fixing rare earth luminescent centers but also functioning as a rigid matrix to stabilize the triplet state of the CDs. Under the excitation of 365 nm ultraviolet light and 980 nm near-infrared light, CDs@YF3:Yb,Tm exhibited blue fluorescence and green room-temperature phosphorescence of CDs and upconversion luminescence of Tm3+, respectively. Due to the strong protection of the rigid matrix, the stability of CDs@YF3:Yb,Tm is greatly improved. This work provides a general synthesis strategy for achieving multimode luminescence and high stability of CD-based luminescent materials and offers opportunities for their applications in advanced anti-counterfeiting and information encryption.

Breaking the balance of chemical ratio in ZnAl2O4 to regulate activators and traps for multimode luminescence – A new strategy

As a common transition metal activator, the non-rare earth element Mn has good luminescent properties, so it has been widely concerned. It is reported that Mn2+ and Mn4+ can co-exist in the matrix, and the luminescence of Mn with different valence states is usually controlled by the co-doping of other ions. In this work, we controlled the green light emission of Mn2+, the red light emission of Mn4+, and the NIR emission of defects by breaking the balance of chemical ratio in ZnAl2O4:Mn to achieve multimode luminescence. The spinel-structured ZnAl2O4 phosphors with deficiency of zinc were synthesized by high-temperature solid-state reaction, which were characterized by a series of techniques, including XRD, DFT calculation, PLE/PL spectroscopy, TL, persistent luminescence decay curves, and temperature-dependent PL spectra analysis. The deficiency of zinc results in the appearance of zinc vacancy (VZn) and oxygen vacancy (VO), and the increased oxygen vacancy defects inhibit the self-reduction of Mn4+. Under the excitation of 325 nm and 426 nm ultraviolet light, the phosphor showed green emission at 510 nm, red emission at 678 nm, and near-infrared emission at 767 nm. Due to the increase of vacancy defects, the higher concentration of zinc deficiency leads to stronger emission of green light, red light, and near-infrared light. The phosphor exhibited different light signals at different excitation wavelengths, and the thermal stability of Mn2+ and Mn4+ luminescence is inconsistent. The above characteristics show that the multimode luminescent phosphor synthesized in this work has broad application prospects in the field of fluorescence anti-counterfeiting.

Trap engineering in ZnGa2O4:Tb3+ through Bi3+ doping for multi-modal luminescence and advanced anti-counterfeiting strategy

Optical information encryption based on luminescence materials have received much attention recently. However, the single luminescence mode of the luminescence materials greatly limits its anti-counterfeiting application with high safety level. Here, a series of luminescence materials of Tb3+ and Bi3+ co-doped ZnGa2O4 phosphors with great correspondence in photoluminescence (PL), persistent luminescence (PersL), and thermoluminescence (TL) modes was synthesized by the conventional solid-phase method for the application in multi-modal anti-counterfeiting fields. Under the excitation of 254 nm, ZnGa1.99O4:0.01 Tb3+, yBi3+ (y = 0.001,0.002) sample exhibited a broad blue emission band (the transition from [GaO6]) at 440 nm and the characteristic emission peaks of Tb3+ at 495 nm, 550 nm, 591 nm and 625 nm, corresponding to the transitions of 5D4-7Fn (n = 6, 5, 4, 3), respectively. Interestingly, the co-doping of Bi3+ ions improve the crystallinity and particle size of the phosphor, subsequently enhanced the PL intensity of Tb3+ to 6 times that of Tb3+ singly doped ZnGa2O4 phosphor. Further, the flexible films with multi-modal luminescence properties have been fabricated through the unique TL and PersL characteristics of ZnGa2O4: Tb3+, Bi3+ phosphors, including “Optical information storage film”, “snowflake and characters” and “QR code”. Moreover, a set of optical information encryption is obtained by combining ZnGa2O4:Tb3+, Bi3+ phosphor and red emitting phosphor. The results indicate that ZnGa2O4:Tb3+, Bi3+ phosphor with multi-modal stimulus response can be expected to be potentially used in the applications of optical information storage and anti-counterfeiting fields.

Thermo-enhanced afterglow emission in Tm3+ doped fluoride nanoparticles for anti-counterfeiting application after X-ray excitation

Multimodal luminescence has emerged as a promising solution in the realm of anti-counterfeiting techniques, which have gained global attention due to their association with information and data security. The conventional approach to achieving multimodal luminescence typically involves combining upconversion and downshifting luminescence, which necessitates the use of external excitation sources and costly detection equipment. Herein, we develop an anti-counterfeiting strategy based on the afterglow performance of NaLuF4: Gd, Tm nanoparticles after X-ray excitation. The X-ray-induced Frenkel defects-base traps ensnare electrons with low kinetic energy, resulting in the creation of persistent photon traps that are responsible for the temperature-dependent afterglow intensity. The dual-band and thermo-enhanced afterglow emission can encrypt information well according to our proof-of-concept experiment and the visible light signal can be successfully captured by a smartphone camera. These unique features of NaLuF4: Gd, Tm nanoparticles render them highly appealing for multilevel anti-counterfeiting applications.

Tuning Oxygen Vacancy in CaZnOS through Cation Substitution for Substantially Enhanced Multimode Luminescence of Mn2+ and Tb3+

AbstractCurrent luminescence materials are abundantly available for visualization fields on a theoretical level, while the lack of luminescent intensity has largely hindered their practical application. Here, the substantial enhancement of the multimode luminescence is demonstrated including mechanoluminescence (ML), photoluminescence (PL), and X‐ray excited optical luminescence (XEOL) for Mn2+ and Tb3+ in zinc calcium oxysulfide (CaZnOS) by increasing the concentration of oxygen vacancies (OVs). Through a comprehensive structure analysis, it is found that the CaZnOS lattice has a tolerance of 60% of Sr2+ with respect to Ca2+ in the methodology. The experimental characterizations verified that the lattice distortion of CaZnOS originating from Sr2+ incorporation can efficiently promote the elimination of oxygen elements and simultaneously produce more OVs in the matrix, which can effectively fortify the trapped electrons and ultimately promote stronger luminescence. The ML, PL, and XEOL achieve around two to six times’ enhancement after Sr2+ incorporation. The findings provide insight into mechanisms underlying the luminescence behavior change of phosphors after cation substitution and may have wide implications for the practical application of intrinsically defective phosphors.

Pure Green Upconversion from a Multicolor Downshifting Perovskite Crystal

AbstractLanthanide‐doped halide perovskite has emerged as a promising phosphor for multimode luminescence. Here, a chloride‐based perovskite single crystal is reported, namely Cs2NaInCl6:Yb3+,Er3+, that is grown in a hydrothermal reactor. The as‐grown crystals feature two distinct luminescence behaviors under UV and 980 nm laser excitation, respectively. Under UV lamp excitation, the crystal shows a multicolor emission of sharp bands at 448, 550, and 660 nm, covering a wide color gamut in CIE diagram. In stark contrast, the crystal under 980 nm excitation exhibits a pure green upconversion with a green‐to‐red ratio up to 211. The universal green dominance is further demonstrated in many chlorides, including Cs2AgInCl6, Cs2NaBiCl6, and Cs2AgBiCl6. The strong green upconversion is used for optical thermometry, which demonstrates an unprecedented sensitivity up to 9.3% K−1 at the low temperature end. The work introduces a kind of new hosts for single‐band upconversion luminescence, opening up many possibilities in areas such as low‐threshold laser and pure‐green color converter.

High-efficiency dual-mode luminescence of metal halide perovskite Cs3Bi2Cl9:Er3+ and its use in optical temperature measurement with high sensitivity

Metal halide perovskites have attracted much attention due to their excellent optical properties and structural tunability. In this work, we synthesized the metal halide perovskite Cs3Bi2Cl9:Er3+ as the activator by solid-phase method using deionized water as the solvent. The phosphor doped with self-sensitizating of Er3+ ions emitted bright green light under the excitation of triple near-infrared laser (808 nm, 980 nm and 1550 nm). Interestingly, the upconversion emission exhibited a strong temperature dependence due to the thermally coupled energy levels 2H11/2 and 4S3/2 of Er3+, therefore is useful for optical temperature measurement. The maximum relative sensitivity in the range of 303–573 K is 1.40%K−1 (303 K, 808 nm), 1.38%K−1 (303 K, 980 nm), 1.50%K−1 (303 K, 1550 nm), respectively. By using fluorescence intensity ratiometry (FIR) methods, Cs3Bi2Cl9:Er3+ phosphor showed excellent accuracy and sensitivity and was compared very favorably with the reported temperature measurement materials. We anticipate that this new phosphor may have a range of applications in multi-mode luminescence and multi-excited light source temperature measurement.

Broadband and Multimode Near‐Infrared Emitter Based on Cr3+‐Activated Stannate for Multifunctional Applications

AbstractBroadband near‐infrared (NIR) phosphors have recently received considerable attention in spectroscopy technology fields, but designing inexpensive, emission peaks centered above 800 nm, and multimodal broadband NIR luminescence material still remains a great challenge. Here, by selecting stannate compound Mg2SnO4 (MSO) as the host, a kind of broadband NIR phosphor MSO:Cr3+ with multimode luminescence properties is reported. The designed material exhibits an emission peaking at 800 nm and a full‐width at half maximum of 180 nm (≈2730 cm−1). The site occupation of Cr3+ in MSO is unraveled by density functional theory calculation. The constructed NIR light‐emitting device based on MSO:Cr3+ displays a high NIR output power of 187.19 mW@100 mA and remarkable photoelectric efficiency of 13.67%, and its multifunctional applications in information encryption, non‐destructive detection, and so on are also demonstrated. Additionally, through defect site reconstruction, MSO:Cr3+ presents superior broadband NIR persistent luminescence (PersL) properties with PersL duration time longer than 50 h. This work provides a feasible strategy to develop intelligent optical material integrated with multimodal luminescence through low‐cost stannate compounds as the host toward versatile applications such as non‐destructive detection and bioimaging.

Multi-Mode Lanthanide-Doped Ratiometric Luminescent Nanothermometer for Near-Infrared Imaging within Biological Windows

Owing to its high reliability and accuracy, the ratiometric luminescent thermometer can provide non-contact and fast temperature measurements. In particular, the nanomaterials doped with lanthanide ions can achieve multi-mode luminescence and temperature measurement by modifying the type of doped ions and excitation light source. The better penetration of the near-infrared (NIR) photons can assist bio-imaging and replace thermal vision cameras for photothermal imaging. In this work, we prepared core-shell cubic phase nanomaterials doped with lanthanide ions, with Ba2LuF7 doped with Er3+/Yb3+/Nd3+ as the core and Ba2LaF7 as the coating shell. The nanoparticles were designed according to the passivation layer to reduce the surface energy loss and enhance the emission intensity. Green upconversion luminescence can be observed under both 980 nm and 808 nm excitation. A single and strong emission band can be obtained under 980 nm excitation, while abundant and weak emission bands appear under 808 nm excitation. Meanwhile, multi-mode ratiometric optical thermometers were achieved by selecting different emission peaks in the NIR window under 808 nm excitation for non-contact temperature measurement at different tissue depths. The results suggest that our core-shell NIR nanoparticles can be used to assist bio-imaging and record temperature for biomedicine.

Multicolor and multimode luminescence regulation and anti-counterfeiting application of lanthanide ions doped Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> phosphors

Multicolor and multimode luminescence materials have important applications in the field of information security encryption. However, the design and synthesis of multicolor multimode luminescent materials is still a challenge, and only several materials have been reported. In this paper, a series of single doped and double doped Li<sub>1–<i>x</i></sub>K<sub><i>x</i></sub>NbO<sub>3</sub>:Pr<sup>3+</sup>/Er<sup>3+</sup>/Tm<sup>3+</sup> phosphors are prepared by high temperature solid state method. The structure, morphology, optical properties and thermoluminescence (TL) spectra are characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), luminescence spectrometer and self-made heating device. Firstly, the effects of different values of K<sup>+</sup> content on the luminescence and trap distribution of LiNbO<sub>3</sub> materials are studied. The results show that the ionic lattice is distorted when a small quantity of K<sup>+</sup> ions replace Li<sup>+</sup>. With the addition of K<sup>+</sup>, the photoluminescence excitation (PLE) spectra monitored emission of 620 nm shows that the ratios of the absorption peaks from matrix (200–310 nm) to absorption peaks from the intrinsic transition of Pr<sup>3+</sup> ions 4f→5d (310–430 nm) change significantly, showing a double-peak characteristic. When the concentration of K<sup>+</sup> ions is 0.5, the absorption peak from the matrix disappears, which may be due to the phase transition of the matrix lattice caused by excessive K<sup>+</sup> ions or the introduction of a large number of defect energy levels into the matrix lattice. Moreover, K<sup>+</sup> ion doping can regulate the density and distribution of traps. TL curves show that a small quantity of K<sup>+</sup> doping increases the trap density of shallow traps. When a large quantity of K<sup>+</sup> is doped, the phase changes of matrix lattice and the defect density decrease. Secondly, the doping of Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> matrix by different luminescent centers (Pr<sup>3+</sup>/Er<sup>3+</sup>/Tm<sup>3+</sup>) is studied. The results show that the multicolor luminescence emission in red, blue and green bands and the tunable multimode luminescence (up/down conversion luminescence, afterglow luminescence and photo-stimulated luminescence) are realized by the selective excitation. According to the multicolor and multimode characteristics of the phosphors, a butterfly-shaped anti-counterfeiting pattern is designed. Owing to the different energy level positions of the luminescence centers, dynamic multicolor photoluminescence is realized by selective excitation at different wavelengths. Based on the upconversion luminescence characteristics of Er<sup>3+</sup> and the excellent afterglow characteristics of Pr<sup>3+</sup> in Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> material, the designed anti-counterfeiting pattern shows the dynamic color change and multicolor, multimode high-order anti-counterfeiting application.

Achieving excitation wavelength-power-dependent colorful luminescence via multiplexing of dual lanthanides in fluorine oxide particles for multilevel anticounterfeiting.

The optical characteristics of multimode luminescent materials like multimode luminescence (photoluminescence, afterglow, thermoluminescence) and a multi-excitation source (light, thermal, mechanical force) play crucial roles in optical data storage and readout, document security and anticounterfeiting. A higher level of advanced anticounterfeiting may rely on multimode anticounterfeiting materials that can realize multicolor luminescence. Here, a highly integrated multimode and multicolor Y7O6F9:Er3+,Eu3+ material is developed through multiplexing of dual lanthanides in fluorine oxide particles. In photoluminescence and photoluminescence/up-conversion luminescence modes, the material Y7O6F9:Er3+,Eu3+ has the characteristic of excitation wavelength and power dependence. In the photoluminescence mode, under excitation at 254 nm and 365 nm, Y7O6F9:Er3+ and Y7O6F9:Eu3+ showed bright red and green emissions, respectively. In the photoluminescence/up-conversion mode, under the increased excitation power from 0.2 to 2.0 W cm-2, the color of luminescence emission can be finely tuned from red to orange, yellow and green. Taking this unique excitation wavelength-power-dependent luminescence property into account, a multilevel anticounterfeiting device with the Lily pattern was designed. The device readily integrates the advantages of the excitation wavelength-dependent photoluminescence emissions and excitation power-dependent photoluminescence emissions in one overall device. These findings offer unique insight for designing highly integrated multimode, multicolor luminescence materials and advanced anticounterfeiting technology toward a wide variety of applications, particularly multilevel anticounterfeiting devices.

Achieving multicolour and multimodal luminescence in Ca3Al2Ge3O12:Bi3+/Ln3+(Ln = Tb, Eu, Sm, and Dy) persistent phosphors for multiple applications

Ca3Al2Ge3O12:Bi3+/Ln3+(Ln = Tb, Eu, Sm, and Dy) persistent phosphors can provide advanced anti-counterfeiting and fingerprint identification.

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.

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 TiGd 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.

Deep-red to NIR mechanoluminescence in centrosymmetric perovskite MgGeO3: Mn2+ for potential dynamic signature anti-counterfeiting

Developing deep-red to near infrared (NIR) materials with multi-mode luminescence is challenging, which has promising utilization in various applications such as stress sensing and dynamic signature anti-counterfeiting. Different to the mainstream non-centrosymmetric mechanoluminescence (ML), a centrosymmetric perovskite compound (MgGeO3: Mn2+) ML material is reported. Deep-red to NIR light (600–800 nm) from Mn2+ ion is confirmed, which is attributed to the strong crystal field within the [MgO6] polyhedron. The stiffness tetrahedral units and large defect accommodating space within the host are favorable for both ML and persistent luminescence (PersL). Mn2+ ion is the only luminescent center, which is confirmed by spectral characterizations. Based on diffuse reflectance spectra, thermoluminescence analysis and density functional theory calculations, the inherent relationship between PersL, ML and PL is further clarified in detail. Due to the formation of MnMg defects, shallow trap significantly become shallower after adding Mn2+ ions. This study reports a Mn2+-doped deep-red to NIR ML phosphor, and further describes the PersL and ML mechanisms via defect engineering regulation. In general, this study may also open up a new approach for the development of efficient NIR ML materials, and show various potential applications such as in anti-counterfeiting and information encryption fields.