Multicolor Luminescence Research Articles

Multicolor Tunable Upconversion Luminescence via Near‐Infrared Manipulation of Population Pathways of Er3+ Ions Excited‐State Levels for Volumetric Color Displays

AbstractPrecise control over multicolor luminescence of upconversion nanoparticles (UCNPs) is of significant importance for their applications in widespread fields of research. However, realizing the tunable emissions in single UCNPs with a single lanthanide element remains a great challenge. Herein, without multiple lanthanide elements, a new strategy for the regulation of the excited‐state level population pathways of the same lanthanide activator Er3+ ion to obtain multicolor‐tunable upconversion luminescence is proposed through utilizing 980 nm coupled 1973 nm synergistic excitation. Unlike typical single wavelength excitation, the synergistic excitation may affect population pathways of the excited‐state level of Er3+ ion by adjusting excitation wavelength and power density, resulting in a dynamically adjustable change in luminescence color output. Notably, multicolor luminescence involving green, chartreuse, yellow, orange, and red can be tuned dynamically in the NaYF4:Er3+ single UCNPs by using the tunable 980/1973 nm synergistic excitation. This dynamic luminescence color variation from these UCNPs has demonstrated promising potential applications in volumetric color display. The results provide a new approach to achieve multicolor‐tunable upconversion luminescence at single nanoparticles level and open up the possibility of developing true three‐dimensional volumetric color display technologies with resolution at the nanometer range.

Self-reporting and Biodegradable Thermosetting Solid Polymer Electrolyte.

To date, significant efforts have been dedicated to improve their ionic conductivity, thermal stability, and mechanical strength of solid polymer electrolytes (SPEs). However, direct monitoring of physical and chemical changes in SPEs is still lacking. Moreover, existing thermosetting SPEs are hardly degradable. Herein, by overcoming the limitation predicted by Flory theory, self-reporting and biodegradable thermosetting hyperbranched poly(β-amino ester)-based SPEs (HPAE-SPEs) are reported. HPAE is successfully synthesized through a well-controlled "A2+B4" Michael addition strategy and then crosslinked it in situ to produce HPAE-SPEs. The multiple tertiary aliphatic amines at the branching sites confer multicolour luminescence to HPAE-SPEs, enabling direct observation of its physical and chemical damage. After use, HPAE-SPEs can be rapidly hydrolysed into non-hazardous β-amino acids and polyols via self-catalysis. Optimized HPAE-SPE exhibits an ionic conductivity of 1.3×10-4 S/cm at 60 °C, a Na+ transference number ( ) of 0.67, a highly stable sodium plating-stripping behaviour and a low overpotential of ≈190 mV. This study establishes a new paradigm for developing SPEs by engineering multifunctional polymers. The self-reporting and biodegradable properties would greatly expand the scope of applications for SPEs.

Self‐reporting and Biodegradable Thermosetting Solid Polymer Electrolyte

AbstractTo date, significant efforts have been dedicated to improve their ionic conductivity, thermal stability, and mechanical strength of solid polymer electrolytes (SPEs). However, direct monitoring of physical and chemical changes in SPEs is still lacking. Moreover, existing thermosetting SPEs are hardly degradable. Herein, by overcoming the limitation predicted by Flory theory, self‐reporting and biodegradable thermosetting hyperbranched poly(β‐amino ester)‐based SPEs (HPAE‐SPEs) are reported. HPAE is successfully synthesized through a well‐controlled “A2+B4” Michael addition strategy and then crosslinked it in situ to produce HPAE‐SPEs. The multiple tertiary aliphatic amines at the branching sites confer multicolour luminescence to HPAE‐SPEs, enabling direct observation of its physical and chemical damage. After use, HPAE‐SPEs can be rapidly hydrolysed into non‐hazardous β‐amino acids and polyols via self‐catalysis. Optimized HPAE‐SPE exhibits an ionic conductivity of 1.3×10−4 S/cm at 60 °C, a Na+ transference number ( ) of 0.67, a highly stable sodium plating‐stripping behaviour and a low overpotential of ≈190 mV. This study establishes a new paradigm for developing SPEs by engineering multifunctional polymers. The self‐reporting and biodegradable properties would greatly expand the scope of applications for SPEs.

Metal-Free organic polymeric room temperature phosphorescence system with Multi-Colour and ultralong lifetime

Room-temperature-phosphorescent (RTP) metal-free organic polymer materials with long-lasting luminescence properties have received considerable attention in the field of optical materials. Herein, we report unique RTP polymeric materials with ultralong-lasting multicolor luminescence prepared using a series of organic phosphorescent guest molecules and melamine formaldehyde resins. Because of facile thermal cross-linking, these materials exhibit a stable multicolor long-lasting afterglow with a maximum phosphorescence lifetime of > 1 s and a maximum phosphorescence emission efficiency of up to 3.4 %. In addition, polymer doping systems with flexible processability were easily printed on 2D substrates and further used as patterned security labels with full-color dynamic phosphorescence. Further, different materials were combined to form a ternary digital encryption system. In addition, although reports on 3D-printed phosphorescent materials are scarce, by using a similar thermoforming method, we successfully prepared a 3D-molding phosphorescent material that can exhibit a satisfactory long-lasting afterglow even after it is kept underwater for 30 days. In conclusion, this work will usher in advancements in the development and application of metal-free polymer-based RTP materials with long-lasting luminescence and 3D printing potential.

Tunable afterglow Ca1 - xSrxAl2O4:Eu2+, Nd3+ phosphors with dependence of an excitation wavelength.

In the emerging field of high-capacity information encryption, multicolor, multitemporal, and multimodal luminescence inorganic materials are of great significance. However, conventional inorganic materials lack the flexibility to dynamically adjust the photon transition path, resulting in unicolor luminescence of the sample and reducing the reading and decoding levels. Herein, we elaborately designed the components for constructing dual-phase crystal fields for Eu2+ in phosphors based on a high temperature solid-state method. Specifically, SrAl2O4:Eu2+ crystal with a bright green afterglow and CaAl2O4:Eu2+ crystal with a blue afterglow were obtained in phosphors at the same time. As a result, a tunable afterglow behavior from blue to white was achieved due to the 4f65d1 → 4f7 transition of Eu2+ at different crystal field sites. Finally, the color tunable afterglow sample was used to explore the encryption and decryption processes of information, and the results showed that the prepared material has a good anti-counterfeiting performance, which is promising for the development of long persistent luminescent materials.

Multistimuli-responsive multicolor solid-state luminescence tuned by NH-dependent switchable hydrogen bonds.

Revealing the stimuli-responsive mechanism is the key to the accurate design of stimuli-responsive luminescent materials. We report herein the multistimuli-responsive multicolor solid-state luminescence of a new dicopper(I) complex [{Cu(bpmtzH)}2(μ-dppa)2](ClO4)2 (1), and the multistimuli-responsive mechanism is clarified by investigating its four different solvated compounds 1·2CH3COCH3·2H2O, 1·2DMSO·2H2O, 1·4CH3OH, and 1·4CH2Cl2. It is shown that luminescence mechanochromism is associated with the breakage of the hydrogen bonds of bmptzH-NH with counter-ions such as ClO4- induced by grinding, while luminescence vapochromism is attributable to the breaking and forming of hydrogen bonds of dppa-NH with solvents, such as acetone, dimethylsulfoxide, and methanol, caused by heating and vapor fuming. In addition, those results might provide new insights into the design and synthesis of multistimuli-responsive multicolor luminescent materials by using various structure-sensitive functional groups, such as distinct N-H ones, to construct switchable hydrogen bonds.

Cluster-induced aggregation in polyurethane derivatives with multicolour emission and ultra-long organic room temperature phosphorescence

Cluster-induced aggregation, multicolour luminescence and ultra-long phosphorescence (0.45 s) in NCLPs based on polyurethane derivatives have been achieved by simply adjusting reaction temperature and reaction time; this is the longest reported phosphorescence lifetime for pure NCLPs.

Fast and versatile electrodeposition of vertically aligned layered rare-earth hydroxide nanosheets for multicolour luminescence and oil/water separation

LYH films were prepared via electrodeposition on ITO glass and metal mesh. Bases on the new synthesis, oil/water separators and Y2O3:RE films with multicolor luminescence were obtained.

Tm3+ mediated multicolor luminescence of NaYbF4:Er,Tm@NaYF4 for advanced anti-counterfeiting.

Lanthanide doped multicolor luminescent materials have attracted extensive attention due to their advanced anti-counterfeiting properties. However, designing a simple, hard-to-copy and multicolor anti-counterfeiting strategy based on upconversion nanoparticles (UCNPs) remains a huge challenge. Herein, a strategy to modulate luminescence color by altering the mediating action of Tm3+ was proposed. As a proof of concept, the mediating action of Tm3+ was explored in NaYbF4:30%Er,1%Tm@NaYF4 by changing the doping ratio of Yb3+/Er3+/Tm3+, and red, yellow and blue luminescence was successfully obtained. Then, NaYbF4:x%Er,1%Tm@NaYF4 (x = 2, 10, 30, 50, 99), NaYbF4:x%Er@NaYF4 (x = 2, 10, 30, 50, 100) and NaYbF4:1%Tm@NaYF4:x%Er@NaYF4 (x = 2, 10, 30, 50, 100) were synthesized to further identify that the mediating action of Tm3+ was related to the doping ratio and distance between dopant ions. In addition, the luminescence color of NaYbF4:30%Er,1%Tm@NaYF4 changed from red to yellow with the increase of excitation power density. Based on the above, NaYbF4:Er,Tm@NaYF4 UCNPs show excellent performance in anti-counterfeiting of paintings, thus revealing their great potential in advanced anti-counterfeiting applications.

Hydrothermal synthesis, morphology control and tunable luminescence properties of AgTbW2O8:Eu3+ phosphors

In this work, AgTbW2O8:Eu3+ phosphors were synthesized by a one-step hydrothermal method and multicolor luminescence was achieved in a single matrix.

Multicolor and multimodal luminescence in an Er3+ single-doped double perovskite for advanced anti-counterfeiting and encryption

The Er3+ single-doped NaGdTi1.8Al0.2O6 double perovskite material achieves multicolor luminescence, afterglow, and upconversion emission by responding to several types of excitation ranging from UV to NIR and thermal disturbance.

Controllable persistent luminescence in bismuth activated memory phosphors by trap management for artificial intelligence anti-counterfeiting

The management of multicolour and multimode luminescence in persistent luminescence (PersL) materials plays a crucial role in encrypting information to combat forgery. Although luminescent anti-counterfeiting has made significant progresses, anti-counterfeiting...

Multicolor photoluminescence of Cu14 clusters modulated using surface ligands.

Copper nanoclusters exhibit unique structural features and their molecular assembly results in diverse photoluminescence properties. In this study, we present ligand-dependent multicolor luminescence observed in a Cu14 cluster, primarily protected by ortho-carborane-9,12-dithiol (o-CBDT), featuring an octahedral Cu6 inner kernel enveloped by eight isolated copper atoms. The outer layer of the metal kernel consists of six bidentate o-CBDT ligands, in which carborane backbones are connected through μ3-sulphide linkages. The initially prepared Cu14 cluster, solely protected by six o-CBDT ligands, did not crystallize in its native form. However, in the presence of N,N-dimethylformamide (DMF), the cluster crystallized along with six DMF molecules. Single-crystal X-ray diffraction (SCXRD) revealed that the DMF molecules were directly coordinated to six of the eight capping Cu atoms, while oxygen atoms were bound to the two remaining Cu apices in antipodal positions. Efficient tailoring of the cluster surface with DMF shifted its luminescence from yellow to bright red. Luminescence decay profiles showed fluorescence emission for these clusters, originating from the singlet states. Additionally, we synthesized microcrystalline fibers with a one-dimensional assembly of DMF-appended Cu14 clusters and bidentate DPPE linkers. These fibers exhibited bright greenish-yellow phosphorescence emission, originating from the triplet state, indicating the drastic surface tailoring effect of secondary ligands. Theoretical calculations provided insights into the electronic energy levels and associated electronic transitions for these clusters. This work demonstrated dynamic tuning of the emissive excited states of copper nanoclusters through the efficient engineering of ligands.

One-step solvothermal synthesis of full-color fluorescent carbon dots for information encryption and anti-counterfeiting applications.

Multicolor fluorescent carbon dots (CDs) have received extensive attention due to their excellent fluorescence tunable performance. In this study, multicolor CDs with color tunable and high fluorescence quantum yields (QYs) were successfully prepared under the same conditions by a one-step solvothermal method using 2-aminoterephthalic acid (ATA) and Nile Blue A (NBA) as reaction reagents, achieving a wide color field coverage. Detailed studies on the relevant mechanisms have been carried out for blue, green and red CDs, indicating that the regulating mechanism of multicolor luminescence is determined by the size of the sp2 conjugated domains, which is due to the increase of particle size that causes an increase in the size of the sp2 conjugated domains, resulting in the narrowing of the band gap and the red-shift of the emission wavelength. It was found that the CDs have the advantages of simple preparation, high photostability and high quantum yield. They were used as fluorescent ink and mixed with polyvinyl alcohol (PVA) to form CD/PVA composites, which were successfully applied in the field of information encryption and anti-counterfeiting. This work provides a new strategy for the synthesis of panchromatic tunable fluorescent CDs and their application in the field of information encryption and anti-counterfeiting.

A photoinduced electron-transfer strategy for switchable fluorescence and phosphorescence in lanthanide-based coordination polymers.

Smart optical materials with tunable fluorescence and room temperature phosphorescence (RTP) exhibit promising application prospects in the field of intelligent switches, information security, etc. Herein, a tetraimidazole derivative was grafted to one-dimensional lanthanum-diphosphonate through H-bonds, generating a coordination polymer (CP), (H4-TIBP)·[La2Li(H2-HEDP)4(H-HEDP)]·3H2O (termed La; TIBP = 3,3,5,5-tetra(imidazole-1-yl)-1,1-biphenyl; H4-HEDP = 1-hydroxyethylidene-1,1-diphosphonic acid) with a three-dimensional supramolecular structure. La shows dynamic fluorescence from blue to red and switchable monotonous yellowish-green RTP, which can be manipulated by reversible photochromism. It is worth noting that Eu3+/Tb3+-doped CPs exhibit time-resolved (red to yellow) and monotonous green afterglow, respectively, which can be attributed to multiple emissions with different decay rates. The dynamic and multicolor luminescence endows these CPs with potential for application in the domains of optical communications, multi-step encryption, and anti-counterfeiting. This work not only integrates color-adjustable fluorescence, switchable RTP, and photochromism in one material, but also realizes the manipulation of the resultant optical performances via photochromism, paving the pathway for the design and synthesis of smart optical materials.

High-efficiency multicolor fluorescent indoleninonaphthooxazole derivatives with adjustable excitation

Solvatochromic fluorophores are one of the most investigated dyes because they exhibit multi-color luminescence properties as the polarity of the solvent changes. It remains a challenge to regulate solvatochromism with a large emission shift and maintain high fluorescence efficiency from apolar to polar solvents. Herein, we report a new type of solvatochromic fluorophore that exhibits both multicolor solvatochromism and stable high fluorescence efficiency in polar solvents. The unique solvatochromic properties of indoleninonaphthooxazole derivatives are realized by constructing a single carbon-bond-linked coplanar scaffold containing indolenine and naphthooxazole components with different substituents. We propose a possible mechanism to explain the unique solvatochromism. Excited USTS-3 and USTS-4 exhibit LE state in non-polar solvent and different HLCT states in polar solvents with both high luminescence efficiency. And the excitation of USTS-3 and USTS-4 is determined by aggregation states of molecular USTS-3 and USTS-4 under different concentrations, which exhibits different relaxations but share the same luminescence decay pathway. Benefitting from the unique luminescence properties of indoleninonaphthooxazole derivatives, they exhibit potential applications in solvent polarity detection, bioimaging, anticounterfeiting, electroluminescence, and lighting in different matrix. Our results also provide a new perspective on designing novel fluorophores based on indolenine and naphthoxazole moieties.

Multi-color tunable luminescence of SrMoO4: Tb3+, Eu3+ nanophosphors for dual-mode temperature monitoring and multi-dimensional high secure anti-counterfeiting

New lanthanide-doped nanoparticles with unique optical characterisics are highly desirable for non-contact thermal sensing and advanced optical anticounterfeiting. The fluorescence intensity ratio (FIR) nanothermometers with higher relative temperature sensitivity (Sr) offer several advantages over traditional contact-based temperature sensors, including high sensitivity, fast response times, and non-invasive measurement. Herein, we describe the synthesis of nanocrystalline SrMoO4:RE3+ (RE3+= Tb3+ and Eu3+) using co-precipitation method for various optical applications, such as temperature sensing and anti-counterfeiting. These phosphors nanoparticle emit multi-colors by varying the percentage of Eu3+ and Tb3+ ions incorporated into SrMoO4. The maximum absolute sensitivity for multi-mode non-contact temperature measurement based on FIR and the distinct thermal behaviour of Eu3+ and Tb3+ ions was reached at 0.055 K−1. The maximum relative sensitivity is reached at 1.8 % K−1, with a minimum temperature resolution δT of 0.043 K at 300 K and maximum δT of 0.272 K. The developed nanophosphors emit green light when it doped Tb3+ and emit red light when it doped with Eu3+, and both demonstrate distinct changes in their response to temperature variations. The color change with temperature elucidates a real base for potential application in advanced anti-counterfeiting. The co-precipitation method we used to synthesize the nanophosphors is easy to scale up for industrial applications. So, the developed nanophosphors with multicolor emissions is of scientific and technological relevence.

Dynamically photo-tunable multicolor luminescence of supramolecular gel based on fluorescent gelator and used for information encryption

The ingenious collaboration of photo-isomerized molecules and luminescent gelator can create self-supporting materials used for multi-level and multi-dimensional information encryption. Herein, a supramolecular gel (SDTD) was prepared by using photoluminescent gelator 1,3:2,4-di(benzylidene)-D-sorbitol (DBS), lanthanide ions (Tb3+), as well as reversible photo-isomerized diarylethylene (DTE), and spiropyran (SP) derivative. Rheological studies showed that the prepared SDTD gel possessed good self-supporting ability owing to the 3D network structure formed by DBS aggregates. Additionally, SDTD gel displayed dynamic multicolor luminescence due to the presence of three luminescent centers including DBS, Tb3+, and MC-o (the photoisomer of SP). The luminescent color of SDTD gel can be easily tuned by irradiation wavelengths and time. It was found that a photo-tunable fluorescence resonance energy transfer (FRET) occurred between Tb3+ and MC-o, Tb3+ and DTE-c (the photoisomer of DTE), the corresponding FRET efficiency was 47 % and 52 %, respectively. The results also indicated that the photo-tunable inner filter effect (IFE) occurred between DBS and DTE-c, DBS and MC-o, respectively, which endowed SDTD gel with dynamically photo-tunable multicolor luminescence capability. SDTD gel has the advantages of simple preparation, low cost, and flexible luminescence regulation. In addition, based on the multicolor luminescence of SDTD gel, a new method of multi-dimensional information encryption was proposed, which shows a potential application in the field of anti-counterfeiting materials.

Multicolor tunable luminescence and energy transfer of Tb3+/Eu3+ doped NaLaP2O7 pyrophosphate phosphors

The pyrophosphate NaLaP2O7 (NLP) samples doped with Tb3+ and Eu3+ were prepared by a simple high-temperature solid state reaction method. The XRD, SEM and spectroscopy were used for characterization. The phosphors exhibited a pure phase identified by XRD. The powders are aggregates of much smaller particles with individual sizes of about 1 μm or even smaller in diameter. The crystal structures were refined by the Rietveld method, and the unit cell parameters decreased with increasing doping concentration. The luminescence properties of the phosphors are analyzed in detail. The optimal doping concentration was determined to be 16 at.% for NLP:Tb3+ and 10 at.% for NLP:Eu3+. The color tunable luminescence from green to red was achieved by co-doping Tb3+ and Eu3+. The fluorescence dynamics fitting based on the Inokuti-Hirayama model revealed that the energy transfer mechanism is mainly contributed by the electronic dipole-dipole interaction. The energy transfer efficiency from Tb3+ to Eu3+ under 376 nm excitation is more than 50 % when the concentration of Eu3+ exceeds 10 %. Under 376 nm excitation, the emission intensity of NLP:0.16 Tb3+, 0.10Eu3+ at 423 K remains 86 % of that at room temperature, and the quantum efficiency of NLP:0.16 Tb3+, 0.10Eu3+ at room temperature is 44.29 %. The results indicate that the prepared NLP:Tb3+, Eu3+ is potential for pc-WLED applications.

Achieving Multicolor Emitting of Antimony-Doped Indium-Based Halide Perovskite via Monovalent Metal Induced Phase Engineering.

Lead-free metal halide perovskites have attracted attention because of their excellent optical properties and nontoxicity. Here, we report the synthesis of Sb3+-doped indium halide perovskite Cs2InCl5·H2O:Sb3+ by an improved solution coprecipitation method. The treatment of the Sb3+-doped indium halide perovskite with selected monovalent cation halides led to Cs2MInCl6 (Ag+, K+, Na+) in different crystal structures or phases. Sb3+ has an isolated ns2 electron, and Sb3+-doped metal halide acts as the luminescence center and exhibits bright broadband emission that originated from self-trapped excitons. Under UV light excitation, these phosphors with different crystal structures emitted multicolored luminescence ranging from blue, green, yellow, and red depending on whether or not or which monovalent metal ion was used. The phosphor samples were used to print high-resolution 2D color barcodes for security and anticounterfeiting applications. The study presented here provides a new approach for the design and synthesis of lead-free metal halide perovskites with different crystal structures and unique optical properties.