Tunable Luminescence Properties Research Articles

Luminescent metal–organic frameworks as biosensors

Metal-organic frameworks (MOFs) are garnering substantial interest due to their unique structural diversity, tunable pore size, luminescent properties and remarkable multifunction support for biosensing applications including immunoglobulin-M generated against the COVID-19. Recent developments have focused on RT nucleic probes, curative immobilization (enzyme, antibodies or nanoparticles), electrochemical and optical biosensors, along with noninvasive monitoring. In the following feature article, we present an overview of the key advances on MOFs biosensors from few of its branches. We also looked into the rich coordination chemistry between metal nodes and organic linkers which enables a diverse synthetic platform for the pragmatic design of MOF materials with anticipated geometries and properties.

Mn-doping-induced tunable bandgap and luminescence properties of SnO2 nanoparticles grown by SILAR method

In the present study, pure and Mn doped SnO2 thin films were grown by performing successive ionic layer adsorption and reaction (SILAR) method on the glass substrates at room temperature. The fabricated thin films have been studied to assess the influence of Mn doping on structural, morphological, and optical properties of SnO2 crystal lattice. The X-ray diffraction (XRD), Ultraviolet–visible spectrometer (UV–Vis), Energy dispersive X-ray analysis (EDAX), Scanning electron microscope (SEM), Raman, X-ray photoelectron spectroscopy (XPS), and Photoluminescence (PL) spectra measurements were conducted. After the XRD and SEM evaluations, it was found that the grown nanoparticles were in rutile type tetragonal structure of polycrystalline nature which was supported by Raman results. And, the surface morphologies were also observed to be affected from the varied concentrations of Mn doping. Besides, the EDAX evaluation confirmed the integration of Mn content next to Sn and O ions in the synthesized SnO2 nanostructures by SILAR method. The UVi-vis analysis disclosed that the absorbance of the prepared thin films had a clear inclination to increase as doping concentration intensified. In addition to that, the optical investigations also uncovered the bandgap of SnO2 nanocrystallines could be tuned from 2.61 eV to 2.00 eV by exposing them to the different levels of Mn ions. Furthermore, the Photoluminescence spectra evidently acknowledged the possibility of engineering optical characteristics by showing increased luminescent emission intensity values right after the introduction of impurities into the SnO2 lattice. The XPS results further verified the manganese and tin valences existed in the produced thin films.

Tunable luminescence property and optical temperature sensing performance of Bi3+ and Sm3+ co-doped Ca2YZr2Al3O12 phosphors

Researches on tunable luminescence and temperature sensitivity of phosphors have become an increasingly popular trend. This paper reports a series of Ca 2 YZr 2 Al 3 O 12 (CYZA):Bi 3+ , Sm 3+ phosphors prepared by solid-state reaction. The phase purity, energy transfer, luminescent properties and temperature sensing performance of the phosphors have been carefully studied. CYZA:Bi 3+ , Sm 3+ phosphors excited by ultraviolet light show tunable color emission, and the color shifts from dark blue to pink due to Bi 3+ →Sm 3+ energy transfer. The related luminescent mechanism of phosphors is also explained. In addition, according to the different thermal sensitivity of Bi 3+ and Sm 3+ , the temperature sensitivity of the phosphors is studied by fluorescence intensity ratio model. The maximum values of absolute sensitivity and relative sensitivity reach up to 0.099% K −1 at 423 K and 0.356% K −1 at 473 K, respectively. These findings indicate that CYZA:Bi 3+ , Sm 3+ phosphors are potential candidates for tunable luminescence and temperature sensing. • The color-tunable property can be obtained in CYZA:Bi 3+ , Sm 3+ phosphors. • Energy transfer from Bi 3+ to Sm 3+ ions. • Different thermal attenuation behaviors of Bi 3+ and Sm 3+ ions. • Temperature sensing performance is investigated by FIR model.

Energy transfer processes and structure of carboxymethyl cellulose-Tb/Eu nanocomplexes with color-tunable photoluminescence

A series of fluorescent nanocomplexes of carboxymethyl cellulose (CMC)/Terbium (Tb)- Europium (Eu) were successfully synthesized without introducing a second ligand. By adjusting the concentration of the coordinated ions, these nanocomplexes exhibit favorably visibly tunable luminescence properties with colors being able to change from green to red. The XPS analysis demonstrates the formation Tb(III)-O2− and Eu(III)-O2− between OH and COO− in CMC and Tb3+ or Eu3+ ions, which is advantage for light absorption by UV–Vis spectroscopy and fluorescence spectroscopy. The ligand CMC plays a role in coordinating with terbium and europium ions, but also serves as an energy donor to these metal ions by antenna effect. Moreover, the energy transfer also occurred from terbium ions to europium ions in CMC matrix, which is responsible for the tunable luminescence properties of these complexes.

Excitation-induced tunable luminescent properties of polyhedral CaMoO4 microcrystallites

Polyhedral CaMoO4 microcrystallites with excitation-induced tunable luminescent characteristics were successfully synthesized by a hydrothermal method. Polyhedral morphologies with different shapes and exposed facets were observed for the samples prepared at different temperatures. Sharp-vertex polyhedron was obtained at 140 °C due to the increase of (001) surface energy and the sample exhibited the strongest PL emission intensity due to its regular polyhedron morphology. Green and blue light emissions were observed separately under different excitation wavelengths in single CaMoO4 microcrystallites, which can be attributed to the charge transfer transitions within the [MoO4]2− complex and the shallow defects in the bandgap, respectively. The excitation-induced tunable luminescent characteristics make it to be a promising inorganic single-emitting component for optical applications.

Optical properties of multinary copper chalcogenide semiconductor nanocrystals and their applications in electroluminescent devices

In the past few decades, semiconductor nanocrystals (semiconductor quantum dots) have received widespread attention due to their high color purity and size-dependent optical properties as well as their potential applications in the next generation of lightening and displays. At present, most of the emitting layer materials in the quantum-dot electroluminescent devices are focused on cadmium-based chalcogenide quantum dots, but cadmium is harmful to the environment and human health, which faces great challenges in the future commercialization. Therefore, it is necessary to develop an environment-friendly, cadmium-free semiconductor quantum dot with excellent optoelectronic performance. In recent years, multinary copper chalcogenide semiconductor nanocrystals have attracted extensive attention due to their low toxicity, tunable luminescent properties and potential applications in optoelectronic devices. Ternary copper-based chalcogenide semiconductor nanocrystals (such as CuInS2, etc.) can be considered as the counterparts of the II-VI compounds, in which the divalent metal ions (such as Zn2+, etc.) are replaced by monovalent copper ions (Cu+) and trivalent indium ions (In3+). As a result, the crystal structure of ternary I-III-VI nanocrystals is similar to that of II-VI nanocrystals. Up to date, ternary CuInS2 nanocrystals are the most widely studied among different multinary copper chalcogenide semiconductor nanocrystals. The crystal structure of ternary CuInS2 nanocrystals mainly includes sphalerite, wurtzite and chalcopyrite phase, and different-phase CuInS2 nanocrystals often have different optical band gaps. With the development of colloidal chemical synthetic technique, most of the multinary copper chalcogenide semiconductor nanocrystals can be synthesized through a colloidal chemical method. The reaction parameters including temperature, reaction precursor activity and surface ligand in the synthesis process play an important role in the tuning of the size, morphology and composition of the resultant nanocrystals. Generally, ternary CuInS2 nanocrystals have a low photoluminescence quantum yield due to their internal and surface defects. Since most of the multinary copper chalcogenide semiconductor nanocrystals exhibit non-stoichiometric characteristics, the number of copper vacancies also affects their luminescence performance to some extent. In order to improve the luminescence performance, it is a common strategy to introduce Zn2+ into the Cu-In-S system to form a quaternary Cu-In-Zn-S alloyed structure or grow a wide-band gap semiconductor material (such as ZnS) onto its surface to form a core-shell structure. However, due to higher ion mobility of copper ions at a relatively high temperature and the similar radius of Cu+ ion and Zn2+, cation exchange reaction is likely to occur in the epitaxial growth of ZnS shells. Therefore, it is difficult to distinguish the alloyed and core-shell structure for the multinary copper chalcogenide semiconductor nanocrystals. With the in-depth understanding of the relationship between the nanostructure and luminescence properties of multinary copper chalcogenide semiconductor nanocrystals, these nanocrystals have been widely used as light-emitting layers in electroluminescent devices, and a significant progress has been made. At present, different strategies have been exploited to improve the device performance of the electroluminescent devices based on multinary copper chalcogenide semiconductor nanocrystals, such as changing the device structure, regulating the nanostructure of materials, and device interfacial engineering. This review gives a detailed summary on the relationship between the composition, surface ligands, crystal structure as well as the nanostructures and optical properties of the multinary copper chalcogenide semiconductor nanocrystals. Moreover, the progress of electroluminescence devices based on the multinary copper chalcogenide semiconductor nanocrystals is highlighted, and finally the prospect of the development of multinary copper chalcogenide semiconductor nanocrystals is concluded.

Tunable orange, yellow and white emission of Pr3+-doped tungsten gadolinium borate glasses

Pr3+ doped WO3-Gd2O3-B2O3 glasses were prepared by the melt quenching technique to study in the luminescence under different excitation. X-ray diffraction (XRD) pattern represents the dominant vitreous disordered structure. The glass with 2.0 mol% of Pr2O3 possess a massive density at 6.15 g/cm3. The luminescence spectra of Pr3+ doped glasses were recorded under the various excitation wavelengths of visible light and under the electron excitation. The streak camera was used to measure decay time. The developed glasses show tunable luminescence property, orange under 435 and 447 nm excitation, yellow under 471 and 484 nm excitation and white under the electron excitation. The photo- and catodoluminescence decay times of glasses are comparable. The optimal concentration of Pr2O3 in the glass is 0.1 mol% that performed the highest emission intensity. This glass can be considered as a new low-cost alternative for the tunable light source and the electron detection material.

Multi‐Mode Color‐Tunable Long Persistent Luminescence in Single‐Component Coordination Polymers

AbstractMaterials with tunable long persistent luminescence (LPL) properties have wide applications in security signs, anti‐counterfeiting, data encrypting, and other fields. However, the majority of reported tunable LPL materials are pure organic molecules or polymers. Herein, a series of metal‐organic coordination polymers displaying color‐tunable LPL were synthesized by the self‐assembly of HTzPTpy ligand with different cadmium halides (X=Cl, Br, and I). In the solid state, their LPL emission colors can be tuned by the time‐evolution, as well as excitation and temperature variation, realizing multi‐mode dynamic color tuning from green to yellow or green to red, and are the first such examples in single‐component coordination polymer materials. Single‐crystal X‐ray diffraction analysis and theoretical calculations reveal that the modification of LPL is due to the balanced action from single molecule and aggregate triplet excited states caused by an external heavy‐atom effect. The results show that the rational introduction of different halide anions into coordination polymers can realize multi‐color LPL.

Multi-Mode Color-Tunable Long Persistent Luminescence in Single-Component Coordination Polymers.

Materials with tunable long persistent luminescence (LPL) properties have wide applications in security signs, anti-counterfeiting, data encrypting, and other fields. However, the majority of reported tunable LPL materials are pure organic molecules or polymers. Herein, a series of metal-organic coordination polymers displaying color-tunable LPL were synthesized by the self-assembly of HTzPTpy ligand with different cadmium halides (X=Cl, Br, and I). In the solid state, their LPL emission colors can be tuned by the time-evolution, as well as excitation and temperature variation, realizing multi-mode dynamic color tuning from green to yellow or green to red, and are the first such examples in single-component coordination polymer materials. Single-crystal X-ray diffraction analysis and theoretical calculations reveal that the modification of LPL is due to the balanced action from single molecule and aggregate triplet excited states caused by an external heavy-atom effect. The results show that the rational introduction of different halide anions into coordination polymers can realize multi-color LPL.

Luminescence Studies of Pyrochlore Metal Oxide Nanomaterials

Designing lanthanide doped luminescent materials especially nanomaterials with multifunctional applications is highly challenging and demanding. The chemistry and structure of the host materials for lanthanide ions are critical in the selection of known phosphors and in the discovery of new phosphor materials for being used for the applications. Materials with A2M2O7 pyrochlore composition recently have displayed a variety of advanced applications in solid oxide fuel cells, photocatalysis, thermographic phosphor, thermal barrier coating, X-ray scintillator, photoluminescence, and nuclear waste host, etc. In the past few years, we have focused on the studies of pyrochlore AIII 2MIV 2O7 nanoparticles (NPs, where A = trivalent heavy element ions of both lanthanides and actinides, and M = Zr4+, Hf4+, etc.) useful for solid-state lighting, X-ray scintillators, thermometry, and bioimaging. We have achieved substantial tunability of their particle size, crystal phase, and more importantly, luminescence properties. We have gained a clear understanding of the influences of synthesis conditions, particle morphology and composition on their photoluminescence and radioluminescence. The tunable luminescence properties of these lanthanide doped pyrochlore NPs indicate their great application potentials in solid-state lighting and multicolor luminescence devices.

Tunable electronic band structure, luminescence properties and thermostability of (Gd1–xLax)2Si2O7:Ce scintillator by adjusting La/Gd ratio

Mixed crystal strategy is an effective approach of improving the luminescence properties of optical materials and has been adopted widely in many systems. In this paper, the La-mixed Gd2Si2O7:Ce polycrystalline samples were successfully synthesized by a sol-gel method. The crystal structure and luminescence properties were confirmed and discussed by XRD, UV-Vis luminescence spectra, and XEL, respectively. The vacuum ultraviolet excitation spectra and thermoluminescence glow curves were also systematically investigated and discussed at varied temperature. A combination of the first-principles calculations and optical characterization experiments was employed to study the electronic band structure of host material, revealing that the band gap is narrowed and the 5d1 level of Ce3+ shifts to higher energy as the La content increases. The luminescence thermo-stability and activation energy were also measured and calculated. It indicates that thermo-stability is strongly dependent on the La concentration. An effective approach is developed to tune the electronic band structure, luminescence properties and thermostability of (Gd1–xLax)2Si2O7:Ce scintillator by adjusting La/Gd ratio.

Energy Transfer in Metal–Organic Frameworks and Its Applications

Photonic functional materials with designable and tunable energy transfer (EnT) processes have become increasingly popular as they significantly broaden the landscape of currently available luminescent materials. Metal–organic frameworks (MOFs), which are constructed from organic ligands and metal ions/clusters, possess highly ordered networks and tunable luminescent properties that make them excellent platforms for exploring EnT mechanisms and designing directional EnT processes. Although the EnT processes in MOFs have been extensively studied, the intricacies of the mechanisms between multiple emitting centers are still relatively unexplored. Thus, the rational design of tunable luminescent materials is quite arduous without a comprehensive understanding of these underlying mechanisms. In this review, the basic theories behind MOFs is systematically introduced from the perspective of the inherent EnT processes. The use of MOFs as ideal platforms for studying EnT processes and developing an efficient engineering strategy for enhancing luminescence and facilitating novel optical behaviors is highlighted. In addition, applications utilizing EnT in MOFs are emphasized, and the future prospects for the development of this technology are discussed.

Luminescence color tuning of Ce3+ and Tb3+ co-doped Ca2YZr2Al3O12 phosphors with high color rendering index via energy transfer

Originating from the precise control of the luminous color, the development of phosphors with color tunable and single-component white-emitting luminescence properties has always been the focus of high-quality white LED research. Herein, we report that a promising candidate of Ca2YZr2Al3O12: Ce3+, Tb3+ (CYZA: Ce3+, Tb3+) phosphors can be excited by near ultraviolet light (n-UV) to meet the above requirements. The Ce3+ and Tb3+ co-doped garnet-type Ca2YZr2Al3O12 with blue, cyan and green-emitting were synthesized by the conventional high temperature solid-state reaction in air atmosphere. The X-ray diffraction, photoluminescence at room temperature and variable temperature, fluorescent lifetime measurements were characterized to analyze the crystal structure, luminous performance, energy transfer mechanism and thermal stability behavior in detail. As-prepared samples displayed tunable photoluminescence based on the energy transfer from Ce3+ to Tb3+ upon n-UV excitation. More importantly, CYZA: Ce3+, Tb3+ doped with a certain amount of Eu3+ remain single-phase and possess high color rendering index up to 90. The as-fabricated WLED device shows a white light-emitting with the chromaticity point of (0.3578,0.3790) at CCT of 4673 K, which can be further improved via optimizing the ratio of sensitized and activated ions. These results suggest that it possess a great potential as high-quality luminescent materials for the design of white LEDs with excellent performance.

Functional DNA Structures and Their Biomedical Applications

Since the discovery of the double-helix structure in 1953, nucleic acids have been developed from natural genetic codes into functional building blocks in a wide range of biotechnology and material...

Warm white emission of LaSr2F7:Dy3+/Eu3+ NPs with excellent thermal stability for indoor illumination

The novel single Dy3+-activated and Dy3+/Eu3+ co-activated LaSr2F7 NPs-based phosphors were successfully synthesized via a simple precipitation reaction method at room temperature. The phase formations and cell parameters of single Dy3+-activated and Dy3+/Eu3+ co-activated LaSr2F7 NPs were verified in detail by the Rietveld refinement technique based on the recorded X-ray diffraction patterns. The doping concentration of single Dy3+-activated LaSr2F7 NPs was optimized to be 0.1 mol with the concentration quenching dominated by the electric dipole-dipole interaction. Meanwhile, a variety of Eu3+-activated La0.9Sr2F7:0.1Dy3+ NPs exhibited tunable luminescent properties and emitted warm white light in close to standard warm white light under 363 nm excitation. The valid energy transfer (ET) efficiency from Dy3+ to Eu3+ ions was estimated to be about 86.02% based on the emission intensity while the electric dipole-quadrupole interaction dominated the concentration quenching mechanism in ET process. Eventually, the thermal quenching of the obtained samples was studied, showing the excellent thermal stability. All the results manifest that Eu3+-activated LaSr2F7:Dy3+ NPs could emit warm white light with excellent thermal stability for indoor illumination.

Color tunable upconversion luminescence and optical thermometry properties of mixed Gd2O3:Yb3+/Ho3+/Er3+ nanoparticles prepared via laser ablation in liquid

The mixtures of Gd2O3:Yb3+/Er3+ and Gd2O3:Yb3+/Ho3+ nanoparticles were successfully prepared via pulsed laser ablation in liquid followed by solution mixing. Under excitation of 980 nm diode laser, tunable color from green to red emission was achieved. Based on the thermal linked energy levels, the temperature sensitive upconversion emission was observed. The fluorescence intensity ratio (FIR) of I513–530 nm/I530–580 nm increased as the elevation of temperature. The absolute sensitivity and relative sensitivity were derived from temperature dependent FIR. The results show that the mixture of Gd2O3:Yb3+/Er3+ and Gd2O3:Yb3+/Ho3+ nanoparticles are not only potential candidates for multicolor upconversion luminescence but also promising optical materials for non-contact optical thermometry.

Carbon nanodots with tunable luminescence properties synthesized by electrical discharge in octane

We report on the one-step synthesis of luminescent carbon nanodots (C-dots) via an electrical discharge between two graphite electrodes submerged into organic solvent (octane). This is a simple approach for the fabrication of C-dots with tunable photoluminescence (PL) that differs from the other preparation methods, as no post-passivation step is required. The synthesized carbon nanoparticles are of spherical shape and their size is distributed in the range of 2–5 nm and exhibit luminescence sensitive to excitation wavelength.

Investigations on energy transfer mechanism and tunable luminescent properties of Co-doped Ca9La(PO4)7:Dy3+,Eu3+ phosphors

The synthesized Ca9La(PO4)7:Dy3+,Eu3+(CLPO:Dy3+,Eu3+) phosphors were analyzed by phase structure, optical performance, thermal stability and lifetime. The XRD pattern indicated that both the matrix and rare earth ion-doped phosphors were pure phases, and the crystal structure was confirmed as trigonal system. Upon 351 nm excitation, Dy3+-doped CLPO phosphors performed two strong emission peaks at 481 nm and 573 nm. The energy transfer phenomenon from Dy3+ to Eu3+ can be found in the Dy3+, Eu3+ co-doped CLPO phosphors, and the color was tuned from red to blue upon 395 nm excitation with Eu3+ concentration decreasing. The energy transfer characteristic was evidenced by the excitation spectra, emission spectrum and decay time of the synthesized phosphors, and the mechanism of energy transfer from Dy3+ to Eu3+ was evaluated as a dipole–quadrupole interaction. In addition, temperature-dependent spectra were performed and the activation energy was further evaluated about 0.1902 eV. The results indicate the potential application of CLPO:Dy3+,Eu3+ phosphors in white LEDs.

Red shift properties, crystal field theory and nephelauxetic effect on Mn4+-doped SrMgAl10-yGayO17 red phosphor for plant growth LED light

The discovery of novel Mn4+-doped oxide red phosphor with suitable spectrum for plant growth is a hot issue in the recent years due to the characteristic red photoluminescence of 2Eg → 4A2 transition in Mn4+ ions. Generally, the emission position of Mn4+ is hard to tune because of specific crystal field in most phosphors. In this work, tunable luminescence property with obvious red shift in the spectra is observed in the Mn4+-doped SrMgAl10-yGayO17 red phosphor via simple substitution of Ga3+ for Al3+, and crystal field theory and nephelauxetic effect are employed to explain this phenomenon. Meanwhile, the Ga3+ dopant changes the shape of the spectra because Ga3+ dopant guides the replacement site of Mn4+ and changes the luminescence center. Improved emission intensity is obtained because appropriate Ga3+ doping leads to larger band gap and reduces non-radiative transitions. Phosphor-converted LED (pc-LED) devices fabricated with blue chip (470 nm) and the as-obtained SrMgAl10-yGayO17:1.0%Mn4+ phosphors emit bright blue and red light, which fit the absorption regions of plant pigments well, thus SrMgAl10-yGayO17:Mn4+ phosphor can be a candidate for plant growth LED light.

Controllable hydrothermal synthesis and morphology evolution of Zn4B6O13:Tb/Eu phosphors with tunable luminescent properties

A series of Tb, Eu single or co-doped Zn4B6O13 phosphors with tetrahedral morphology were synthesized by facile hydrothermal method. The influences of reaction temperature and the pH value of the reaction system on the structures and compositions of product were also investigated, in which four kinds of zinc borates with different structures and compositions (Zn4B2O7·H2O, Zn4B6O13, Zn(H2O)B2O4·0.12H2O, and H(Zn6O2(BO3)3)) were obtained. A possible growth mechanism of tetrahedral morphology of Zn4B6O13 has been proposed according to reaction time. The obtained samples were characterized by XRD, EDS, SEM, TEM, XPS, BET, DR, PL and QY. XPS results indicate that Eu2+ and Tb4+ are present in Tb/Eu co-doped Zn4B6O13, which might be generated from charge transfer between Tb3+ and Eu3+. The PL results shows that Eu3+, Tb3+ ion single-doped Zn4B6O13 microstructure exhibit orange and green emission under ultraviolet excitation, respectively. Compared to Eu3+ and Tb3+ single doped Zn4B6O13 phosphors, the Eu/Tb co-doped Zn4B6O13 phosphors showed stronger blue emission of Eu2+. These results imply that the tetrahedral morphology of Eu3+, Tb3+ ion single-doped and Eu2+/3+/Tb3+/4+ co-doped Zn4B6O13 phosphors have the promise application for nano/micro-optical functional devices.