Multicolor Luminescence Research Articles

Tunable luminescence and noncontact temperature sensing of oxyfluoride glass ceramics containing Na(Y1.5Na0.5)F6:Bi3+/Eu3+ nanocrystals

The oxyfluoride glass ceramics (GCs) containing novel Na(Y1.5Na0.5)F6 (NYNF) nanocrystals: Bi3+/Eu3+ were successfully fabricated. The results of the transmission electron microscope (TEM) showed that NYNF nanocrystals (40–70 nm) are distributed in the glass matrix. Moreover, the luminescence properties of Bi3+/Eu3+ ions-doped NYNF GCs were tested and analyzed. The NYNF GCs exhibit strong emission at blue (412 nm, Bi3+) and red (613 nm, Eu3+) wavelengths when excited with near-ultraviolet (n-UV) light at 288 nm. The emission color can be adjusted from blue (0.1506, 0.0655) to violet (0.3535, 0.1929) by increasing the Eu3+ ion content. Notably, the sample exhibited significant temperature-sensing characteristics as calculated by fluorescence intensity ratio (FIR), with high relative sensitivity (1.731 % K−1) at 548 K. These findings demonstrate the potential application of NYNF: Bi3+/Eu3+ GCs in achieving tunable multicolor luminescence and noncontact temperature measurement.

A sandwiched luminescent heterostructure based on lanthanide‐doped Gd2O2S@NaYF4 core/shell nanocrystals

AbstractLanthanide (Ln3+) oxysulfide nanocrystals (NCs) have great prospect in many advanced technologies; however, they suffer from a low photoluminescence efficiency due to the volatility of sulfur and deleterious surface quenching effect. Herein, we report a novel sandwiched luminescent heterostructure based on Ln3+‐doped Gd2O2S@NaYF4 core/shell NCs with tunable sulfur content in the sandwich layer. By means of Eu3+ as the sensitive structural probes, we unravel the ligand‐mediated structure control of the NCs from Gd2O3: Ln3+@NaYF4 to Gd2O2S: Ln3+@NaYF4 with tailored S2– deficiency. Such a sandwich‐type core/shell heterostructure enables us to achieve efficient and multicolor downshifting and upconversion luminescence (UCL), with up to 208.8 folds of enhancement in UCL intensity as compared to that of their core‐only counterparts. These findings provide a general approach for the controlled synthesis of lanthanide oxysulfide@fluoride heterostructure, which offers a new way for the materials design towards diverse emerging applications.

Multi-color luminescence of Sm3+ -doped Na2 YMg2 V3 O12 phosphor potentially applicable in white-LEDs.

A novel multi-color emitting Na2 YMg2 V3 O12 :Sm3+ phosphor was synthesized using a solid-state reaction, and its crystal structure, luminescence properties, and thermal stability were studied. Charge transfer within the (VO4 )3- groups in the Na2 YMg2 V3 O12 host led to a broad emission band between 400 and 700 nm, with a maximum at 530 nm. The Na2 Y1-x Mg2 V3 O12 :xSm3+ phosphors exhibited a multi-color emission band under 365 nm near-ultraviolet (near-UV) light, consisting of the green emission of the (VO4 )3- groups and sharp emission peaks at 570 nm (yellow), 618 nm (orange), 657 nm (red), and 714 nm (deep red) of Sm3+ ions. The optimal doping concentration of Sm3+ ions was found to be 0.05 mol%, and the dipole-dipole (d-d) interaction was primarily responsible for the concentration quenching phenomenon. Using the acquired Na2 YMg2 V3 O12 :Sm3+ phosphors, commercial BaMgAl10 O17 :Eu2+ blue phosphor, and a near-UV light-emitting diode (LED) chip, a white-LED lamp was designed and packaged. It produced bright neutral white light, manifesting a CIE coordinate of (0.314, 0.373), a color rendering index (CRI) of 84.9, and a correlated color temperature (CCT) of 6377 K. These findings indicate the potential of Na2 YMg2 V3 O12 :Sm3+ phosphor to be used as a multi-color component for solid-state illumination.

Tunable multicolor luminescence in vanadates from yttrium to indium with enhanced luminous efficiency and stability for its application in WLEDs and indoor photovoltaics

Tunable multicolor luminescence in vanadates from yttrium to indium with enhanced luminous efficiency and stability for its application in WLEDs and indoor photovoltaics

White light emission and energy transfer of LaMgAl11 O19 :Eu3+ , Tb3+ phosphors.

White-light-tunable LaMgAl11 O19 :x%Tb3+ , y%Eu3+ series phosphors were prepared using the gel-combustion method. The structure and luminescence properties were studied, and the energy transfer of Eu3+ and Tb3+ in the LaMgAl11 O19 system was also discussed. The results showed that the LaMgAl11 O19 matrix exhibited strong emission in the blue-light region under the excitation of ultraviolet light, which resulted in conditions suitable for the preparation of white-light-tunable phosphors. The emission spectra of LaMgAl11 O19 :2%Tb3+ , y%Eu3+ (y = 2%-9%) series phosphors were obtained through optimization experiments. It could be seen from the CIE diagram that by adjusting the doping quantities of Eu3+ and Tb3+ in the LaMgAl11 O19 host, multicolor luminescence and white light emission in a single host could be achieved. By calculating the energy transfer efficiency and critical distance between Eu3+ and Tb3+ series phosphors, the mechanism of energy transfer between Tb3+ and Eu3+ was found to be the interaction between electric quadruples.

Emission color tuning based on core-shell microcrystals through modulation of laser power for anti-counterfeiting

Manipulating color with lanthanide doped upconversion luminescence materials is an excellent approach for anti-counterfeiting, thanks to their abundant energy levels and convenient NIR-to-VIS luminescence property. However, most of the materials are limited by the single-color emission and low photoluminescence efficiency. Herein, pumping-dependent multicolor upconversion luminescence core-shell microcrystals have been obtained through a facile hydrothermal method. In comparison to nanomaterials, core-shell microcrystals possess a smaller surface area-to-volume ratio and fewer surface defects, leading to enhancing the luminescence. A naked-eye recognizable color can be switched from green to blue with increasing the laser power. Furthermore, the mechanism of tunable color with laser power varying has been systematically studied. Due to emission colors of the core-shell materials with excitation power sensitivity and being distinguished by naked-eye easily, core-shell microcrystals reveal promising applications for anti-counterfeiting.

Rare earth ions doped Bi2MoO6 luminescent materials: Pechini sol-gel synthesis, down-conversion and up-conversion multicolor emissions, and potential applications

A series of rare earth ions (Eu3+, Sm3+, Yb3+/Er3+, Yb3+/Ho3+, Yb3+/Tm3+) doped bismuth molybdate (Bi2MoO6) phosphors with excellent multicolor luminescence have been synthesized by a facile Pechini sol-gel method. XRD, EDX, and XPS results confirm the highly crystalline orthorhombic phase of Bi2MoO6 and verify that the rare earth ions (RE3+) are effectively integrated into the Bi2MoO6 matrix. During the synthesis process, the calcination conditions play an important role in obtaining the luminescent host matrix, and the optimal calcination condition for the Bi2MoO6 products is determined of 800 °C for 2 h. The Eu3+ and Sm3+ doped Bi2MoO6 samples display intense red and orange-red light under UV/visible excitation whereas the Yb3+/Ln3+ (Ln = Er, Ho, and Tm) doped Bi2MoO6 materials emit green, green, and blue colors when excited by NIR light. Both down-conversion (DC) and up-conversion (UC) multicolor luminescence are obtained by doping the proper Ln3+ activators into the Bi2MoO6 host. The doping concentrations of various RE3+ ions are optimized to generate advantageous phosphors and the luminescence mechanisms of RE3+ ions are systematically studied. The LED devices fabricated by Bi2MoO6:Yb3+/Ln3+ UC phosphors exhibit dazzling multicolor emissions under an injection current, which directly discloses that the as-prepared materials may be of great potential in LEDs and optoelectronic devices. Interestingly, the Bi2MoO6:Yb3+/Er3+/Eu3+ phosphors can simultaneously exhibit red and yellow-green DC emissions and green UC light under excitation of 464, 488, and 980 nm. The multi-mode emission features illustrate that the as-synthesized phosphors may have application prospects in anti-counterfeiting applications.

Multicolor tunable luminescence and energy transfer mechanism in Gd2O2S: Dy3+, Sm3+ phosphors

High quality single-phase multicolor emission phosphor is a prerequisite for efficient luminescence devices, but the system design and quantity preparation are still facing substantial challenges. Herein, Gd2O2S-based phosphors with high crystallinity, good dispersibility, and relatively good size uniformity were obtained by optimizing the type and components of flux based on the conventional solid-state method. By single-doping system study, the emission properties of matrix and activated ions are expounded, meanwhile the composition and co-excitation wavelength of co-doping system are designed. In the co-doping system, we mainly realized adjustable emission, interionic energy transfer, and application performance analysis. Firstly, multicolor emission in the range of yellow, orange and white was achieved through the modulation of dopant type and concentration as well as excitation wavelength. Secondly, the phenomena of spectral overlap (between Dy3+ and Sm3+), fluorescence intensity change (606 nm of Sm3+) and the monotonically decreasing fluorescence lifetime (Dy3+ at 578 nm) were evidence of energy transfer in the co-doping system. The theoretical fitting demonstrates that the energy transfer process of Dy3+→Sm3+ is primarily based on the quadrupole-quadrupole interaction mechanism. In addition, the cathodoluminescence spectra, temperature-dependent emission spectra, and magnetic properties tests have demonstrated the characteristics of multicolor adjustable emission (electron-beam excitation), excellent thermal stability, and good paramagnetic properties of the co-doping phosphors, further indicating that the Gd2O2S:Dy3+/Sm3+ system phosphors have potential as an excellent optical-magnetic bifunctional material in the fields of luminescence and bioimaging.

Designing multicolor luminescence in Tb3+/Eu3+-codoped KGd2F7 nanoparticles through energy transfer engineering for warm white light-emitting diode

By a facile precipitation method at room temperature, series of Tb3+-doped and Tb3+/Eu3+-codoped KGd2F7 nanoparticles (NPs) were synthesized. Upon 377 nm excitation, Tb3+-doped KGd2F7 NPs possess intense green emissions and their strongest intensities are obtained when Tb3+ ion is 30 mol%, where the corresponding concentration quenching mechanism is electric dipole-quadrupole interaction. As for Tb3+/Eu3+-codoped KGd2F7 NPs, dazzling multi-color emissions are achieved, excited by 377 nm, triggered by the energy transfer (ET) from Tb3+ to Eu3+. Specially, the emitting color is changed from green to yellow and finally to red as Eu3+ content increases. Through systematical discussion based on the emission spectra and decay time, the ET mechanism is decided by dipole-dipole interaction. Moreover, Tb3+/Eu3+-codoped KGd2F7 NPs do not only have high thermal stability but also exhibit admirable quantum efficiency of 65.7% excited by 377 nm. Furthermore, through utilizing the resultant NPs as yellow-emitting components, a warm white light-emitting diode with high color rendering index (85.5) and low correlated color temperature (4323 K) is fabricated, which are insensitive to injection current. Our findings may provide promising luminescence materials with multicolor emissions to meet the requirement of phosphor-converted solid-state lighting.

Difluoromethoxyl bridged substituted 2-cyano-pyrrole based pure organic luminescent liquid crystals towards white light emitting single-molecule

ABSTRACT A series of new luminescent liquid crystals (LLCs) comprised of difluoromethoxy and substituted 2-cyano-pyrrole (CN-Py) bridge with the molecular rigid core were synthesised. Their emission colours could be adjusted facilely and reversibly in a non-invasive manner by simply changing the excitation wavelength at room temperature. A simple and practical approach has been developed to avoid the use of hazardous and highly toxic elemental bromine to achieve a green and environmentally friendly synthesis pathway for difluoromethoxy-bridged liquid crystals. Notably, excitation-dependent multicolour luminescence has been realised in a single molecule of 5CC-CF2O-2Br-CN based on pure organic difluoromethoxy bridged liquid crystal, whose emission colours changes from yellow to blue with a blue shift of excitation wavelength. Interestingly, the CIE coordinates (0.29,0.33) of 5CC-CF2O-2Br-CN is very close to the white light coordinates (0.33, 0.33) under excitation at a wavelength of 335 nm. Therefore, 5CC-CF2O-2Br-CN can be a candidate of promising white light emitting luminescent liquid crystal. This protocol offers efficient access to single-molecule liquid crystal material with white light emission.

A new color-tunable persistent luminescent phosphor-in-glass via radiative energy transfer

Materials with multicolor persistent luminescence (PersL) are desirable in color-on-demand applications, such as dark-light multicolor displays and white-emitting persistent light sources. However, such phosphors with long afterglow duration and high afterglow brightness are rarely reported. In this work, a color-tunable PersL phosphor-in-glass (PiG) was achieved via a radiation energy transfer from Sr2MgSi2O7:Eu2+,Dy3+ (SMS) PersL phosphor to Y3Al5O12:Ce3+ (YAG) color-conversion phosphor. Impressively, 5 wt% SMS and 1.5 wt% YAG co-doped PiG exhibits an afterglow duration of 44 h and an afterglow brightness of 50.9 mcd/m2 60 min after Xe lamp light charging, close to those of the commercial SMS phosphor. Impressively, the PersL color of the PiGs can be tuned from blue to yellow by simply adjusting the YAG content. Our results will provide a facile and effective strategy to produce multicolor PersL materials for practical applications.

A ratiometric aptasensor for simultaneous determination of two estrogens based on multicolor upconversion nanoparticles

Different environmental estrogens (EEs) may coexist in the same foodstuff, necessitating the establishment of a simultaneous detection method. Although there are numerous studies on the detection of EEs, few was reported on the determination of two or more estrogens at the same time except HPLC. Our efforts have been made to develop a ratiometric aptasensor based on multicolor lanthanide-doped upconversion luminescence nanoparticles (UCNPs) to realize simultaneous and sensitive detection of two EEs (bisphenol A and 17β-estradiol). Three types of core-shell UCNPs with excellent luminous properties and distinct emitting colors were successfully synthesized via doping with various lanthanide ions, two of which were conjugated with specific aptamers and act as energy donors, while another one served as a reference. Because of their excellent luminescence quenching performance, ultra-thin metallic MoS2 nanosheets were selected as the energy acceptor. Thus, a ratiometric luminescence aptasensor was established and successfully used for the simultaneous detection of two estrogens in tap water and milk samples, demonstrating its considerable practical application value.

Dual-emitting temperature dependent material based on Bi3+/Eu3+ co-activated Ba2Y2Si4O13 phosphor with multicolor anti-counterfeiting

Bi3+, Eu3+ co-doped Ba2Y2Si4O13 phosphors with multi-color luminescence properties were prepared by high temperature solid state method. The structure, luminescent properties and temperature characteristics were studied by X-ray diffraction, scanning electron microscope, fluorescence spectrum and temperature-dependence of emission spectrum. Ba2Y2Si4O13: Bi3+, Eu3+ phosphors can emit color from cyan to red when the excitation wavelength was changed from 340 nm to 390 nm, which is attributed to that there are two Bi3+ ion emission centers, and their emission intensity will change with the change of excitation wavelength. Moreover, the emission of the phosphor has good temperature sensing characteristics, based on the fluorescence intensity ratio of the two blue emission bands of Bi3+ and the red emission peak of Eu3+, a multimode thermometer with high temperature sensitivity was constructed. At the same time, based on the dynamic luminescence characteristics of the phosphor, the dynamic anti-counterfeiting experiments are designed. Therefore, the results show that the material has a bright prospect in the field of temperature sensing and anti-counterfeiting.

3D Printing of Luminescent Glass with Controlled Distribution of Emission Colors for Multi‐Dimensional Optical Anti‐Counterfeiting

AbstractThe fabrication of multicolor luminescent glass with simultaneous controlling of the distribution of emission colors within a monolithic medium has been a tremendous challenge, which, however, could be attractive for diverse photonic applications from optical storage to information encryption. Here, a space‐selective doping method based on a stereolithographic technique is designed, enabling the control of the doping domain of the active luminescence ions, such as Eu3+, Ce3+, Tb3+, and Pr3+, in 3D‐printed single silica glasses. The printed glass shows intense multicolor luminescence, and the interface between the two doping areas is invisible under natural light. By using this technique, multicolor luminescent glass with pre‐designed emission color distribution is fabricated, which enables facile and nondestructive decryption strategies based on photoluminescence under controlled excitation conditions. Besides, the extending of this strategy by using a femtosecond laser for photopolymerization dramatically improves the printing resolution down to the few‐micron scale, enabling the multi‐dimensional optical storage and encryption in miniaturized glass items. This work not only delineates the potential applications of multicolor luminescent glass for multi‐dimensional anti‐counterfeiting and information storage, but also opens up new avenues for prospective applications in sensing, lasers, and displays based on glasses with spatially engineered optical responses.

A First-Principles Investigation of Structure-Luminescence Activity of Donor-Acceptor-Donor Organic Triad.

Structure-property relationships of different conformers of an organic D-A-D triad are explored to rationalize the structural motif toward photoluminescence activity. In a recent experiment ( Chem. Sci. 2017, 8, 2677-2686), Takeda and co-workers revealed that the PTZ-DBPHZ-PTZ (D-A-D) triad exhibited multicolor luminescence properties and thermally activated delayed fluorescence (TADF) emission. We computationally studied the photophysical properties of the conformers of that D-A-D triad to provide a detailed description of the luminescence activity. Our analysis confirms that the twisting of the axial phenothiazine (PTZ) unit to an equatorial position altered the nature of the S1 state from local to a charge transfer state and was responsible for the large red shift in emission (S1) energy. Calculated fluorescence and intersystem crossing (ISC) rate constants suggest that the prompt fluorescence is turned on for axial-axial conformers while it is turned off for others. Fast reverse intersystem crossing (RISC) from triplet CT to the S1 state (3CT1 → 1CT1), close spacing and effective crossing between 3LE1A, 3CT1 and 1CT1 states cause efficient harvesting of triplet excitons to S1 state, thus enabling TADF emission for equatorial-equatorial conformer.

Multifunctional emitters with TADF, AIE, polymorphism and high-contrast multicolor mechanochromism: Efficient organic light-emitting diodes

Organic multifunctional luminescent materials have drawn growing attention due to their diverse emissive mechanism and potential application in luminescent field. Herein, a series of cyanobenzene-decorated dimethylacridine-quinoline conjugates is designed and synthesized, which exhibit thermally activated delayed fluorescence (TADF), aggregation-induced emission (AIE), polymorphism and multicolor mechanochromic luminescence (MCL) with high contrast beyond 75 nm. Significantly, structure-property investigations via the in-depth analysis of molecular conformations and three-dimensional supramolecular framework of the polymorphic crystals demonstrate that the diverse conformations and abundant noncovalent interactions have a predominant impact on aggregation-dependent TADF property and emission wavelength. The quasi-equatorial conformational electron-donating unit and quasi-planar structural electron-withdrawing segment in aggregation states of the emitter are beneficial for accelerating the rate of the reverse intersystem crossing, enhancing TADF character, and promoting the emission with a bathochromic shift. The organic light-emitting diodes (OLEDs) employing these emitters achieve good device performance with an external quantum efficiency (EQE) of 14.6%.

White light generation by regulating hydrogen bond-sensitive ESPT of naphthalimide dyes

White light emitting systems of pure organic materials have attracted extensive research interest due to their better compatibility and functional scalability. The reported organic white light materials are mainly based on the multi-channel emission regulation of the compound itself or the mixing of multicolor luminescence materials, but studies on the dependence between multicolor luminescence and the external environment are lacking, which limits the application of these materials in areas such as identification and sensing. This paper reports that the 4- or 3‑hydroxyl-substituted naphthalimides NapH1 and NapH2 form intermolecular hydrogen bonds with adjacent molecules in the environment, and undergo excited-state intermolecular proton transfer under irradiation, resulting in blue-yellow or blue-red dual fluorescence emission, respectively. Since the two compounds have different two-color luminescence channels and the two-color intensity ratio is affected by the environment, and the intermolecular hydrogen bond is determined by the hydrogen bond receptor, polarity, and temperature in the environment, the full spectrum from blue to red light and white light emission can be obtained by adjusting the mixing ratio of the two dyes and the solvent polarity and the ambient temperature. This environmentally sensitive white emission is used to detect the alkalinity of different papers, and the dyed paper can be used as a test strip for acid-base vapor detection.

2D Inorganic Framework with Self-Transforming Luminescence Centers for Multicolor Emission

Multicolor luminescence is an attractive and emerging field for next-generation optoelectronic devices, including ultrathin displays, optical sensors, and wearable electronic devices. Currently, it is easy to achieve monochromatic emission, while the highly anticipated realization of multicolor luminescence in two-dimensional (2D) material is still blank. This is because the atomic thickness and structural sensitivity of 2D material make it extremely challenging to introduce multiple luminescent centers into it without structural collapse. Here, for the first time, we have designed a 2D inorganic framework with a wide bandgap and easily substitutable sites to embed self-transforming luminescence centers nondestructively and achieved multicolor emissions spanning from green to orange. These findings can provide a new paradigm for designing new 2D multicolor luminescent materials and extend a large margin of diverse applications.

Facile synthesis, novel structure, multicolor luminescence, and potential applications of lanthanide ions doped bismuth titanate phosphors

A variety of lanthanide ions doped bismuth titanate (Bi4Ti3O12) luminescent materials with eminent down-conversion (DC) and up-conversion (UC) luminescence performance have been fabricated via a facile sol-gel approach. The XRD, XPS, and EDX elemental mapping results confirm the phase structure of orthorhombic Bi4Ti3O12 (BTO), and the lanthanide activator ions occupy the Bi3+ lattice sites in the BTO crystal. Under UV or NIR excitation, the Eu3+, Yb3+/Ln3+ (Ln = Er, Tm, and Ho) doped Bi4Ti3O12 samples exhibit characteristic red, green, blue, and green emissions. The luminescent mechanisms of the BTO:Eu3+ and BTO:Yb3+/Ln3+ samples are discussed based on the energy level diagrams. The doping concentrations of Eu3+, Yb3+, Er3+, Tm3+, Ho3+ ions and annealing temperature and time are optimized, whose optimal values are determined to be 14, 8, 1, 0.4, 1 mol% and 800 oC, 4 h. The as-obtained LED devices fabricated by Bi4Ti3O12:Eu3+ and Yb3+/Ln3+ phosphors exhibit dazzling multicolor visible light emissions from different Ln3+ ions. The results indicate that the as-obtained Ln3+ doped BTO phosphors may be potentially utilized in LED devices and solid-state lighting. Furthermore, the Eu3+ and Er3+ co-doped BTO samples exhibit different DC and UC luminescence spectral profiles when excited at various UV, visible, or NIR wavelengths, revealing their eminent feasibility and great potential in anti-counterfeiting applications.

Phosphor-in-glass with time-evolving multicolor luminescence for dynamic anticounterfeiting

The conventional luminescent materials used in the anticounterfeiting field generally exhibit unicolor output and a single-wavelength excitation mode, resulting in a poor anticounterfeiting effect. Herein, we successfully achieved a new transparent SrAl2O4:Eu2+,Dy3+/CaAlSiN3:Eu2+ phosphor-in-glass (PiG) with dynamic luminescence color variation from red to yellow in hundreds of seconds during the ultraviolet lamp irradiation and green persistent luminescence (PersL) after ceasing excitation. Additionally, the prepared PiG owns excitation wavelength- or doping weight ratio-dependent color-tunable luminescence. As a proof-of-concept experiment, the specially designed SrAl2O4:Eu2+,Dy3+/CaAlSiN3:Eu2+ PiG based flower patterns exhibit dynamic luminescence color variation under a simple ultraviolet lamp, and can be observed for quick discrimination. This work exploits a new perspective for the design of dynamic multicolor anticounterfeiting materials.