Tunable color emission in K_3Gd(PO_4)_2:Tb^(3+),Sm^(3+) phosphor for n-UV white light emitting diodes

A series of K3Gd（PO4）2：Tb3＋,Sm3＋ phosphors were synthesized through solid state reaction. By co-doping Tb3＋ and Sm3＋ into K3Gd（PO4）2 host and singly varying the doping concentration of Sm3＋, ttmable colors from green to yellow and then to orange were obtained in K3Gd（POa）2：Tb3＋,Sm3＋ phosphors under the excitation at 373 nm. The energy transfer process from Tb3~ to Sm3- was verified through luminescence spectra and fluorescence decay curves. Moreover, the energy transfer mechanism was demon- strated to be the quadrupole-quadrupole interaction. The results indicated that K3Gd（POa）2：Tb3＋,Sm3＋ phosphors could be a potential application for n-UV white light emitting diodes.

Color-tunable ultralong organic phosphorescence materials for visual UV-light detection

Ultralong organic phosphorescence(UOP)materials have roused considerable attention in the field of photonics and optoelectronics owing to the feature of long-lived emission lifetimes.However,to develop UOP materials with color-tunability is still a formidable challenge.Here,we report a class of UOP materials containing carbonyl,amino or amide groups,exhibiting colortunable persistent luminescence ranging from blue(458 nm)to yellow-green(508 nm)under different UV wavelength excitation.Taken theoretical and experimental results together,we conclude that the excitation dependent color-tunable UOP emission is ascribed to multiple emission centers from single molecular and aggregated states in crystal.Given color-tunable UOP feature,these materials are used to successfully realize visual UV-light detection.This finding not only provides a strategy to design new organic phosphorescent molecules with colorful emission,but also extends the scope of the applications of purely organic phosphorescent materials.

The fabrication of color-tunable organic light-emitting diode displays via solution processing

Electroluminescent devices based on organic semiconductors have attracted significant attention owing to their promising applications in flat-panel displays.The conventional display pixel consisting of side-by-side arrayed red,green and blue subpixels represents the mature technology but bears an intrinsic deficiency of a low pixel density.Constructing an individual color-tunable pixel that comprises vertically stacked subpixels is considered an advanced technology.Although color-tunable organic light-emitting diodes(OLEDs)have been fabricated using the vacuum deposition of small molecules,the solution processing of conjugated polymers would enable a much simpler and inexpensive manufacturing process.Here we present the all-solution processing of color-tunable OLEDs comprising two vertically stacked polymer emitters.A thin layer of highly conducting and transparent silver nanowires is introduced as the intermediate charge injection contact,which allows the emission spectrum and intensity of the tandem devices to be seamlessly manipulated.To demonstrate a viable application of this technology,a 4-by-4 pixelated matrix color-tunable display was fabricated.

Dual-periodic-microstructure-induced color tunable white organic Ught-emitting devices

In this paper, we demonstrate a color tunable white organic light-emitting devices （WOLEDs） based on the two complementary color strategies by introducing two-dimensional （2-D） dual periodic gratings. It is possible to tune the color in a range between cold-white and warmwhite by simply operating the polarization of polarizer in front of the microstructured WOLEDs. Experimental and numerical results demonstrate that color tunability of the WOLEDs comes from the effect of the 2-D dual periodic gratings by exciting the surface plasmon-polariton （SPP） resonance associated with the cathode/organic interface. The electroluminescence （EL） performance of the WOLEDs have also been improved due to the effective light extraction by excitation and out-coupling of the SPP modes, and a 39.65% enhancement of current efficiency has been obtained compared to the conventional planar devices.

Color tunable upconversion emission in CeO_2:Yb,Er three-dimensional ordered macroporous materials

The three-dimensional ordered macroporous CeO2：Yb,Er materials were prepared, and the influence of doping concentra- tion of Yb3＋ or Er3＋ ions on upconversion property was investigated. Green and red upconversion emissions were observed under the excitation of 980 nm at room temperature. It was found that the ratio of red to green upconversion emission intensity increased with increasing of concentration of the Yb3＋ or Er3＋ ions in the three-dimensional ordered macroporous CeO2：Yb,Er materials. When the concentration of Yb3＋ was 10 mol%, pure red upconversion emission was obtained. The varied mechanism of ratio of red to green upconversion emission intensity was discussed with the concentration of Yb3＋ or Er3＋ ions.

Host–guest materials with room temperature phosphorescence:Tunable emission color and thermal printing patterns

The research of purely organic materials with long afterglow has drawn more and more attention,especially for those with stimulus‐response characteristic.So far,this kind of material is really very scarce and their performance is not good enough.In this study,we successfully developed an efficient heatingresponsive room‐temperature phosphorescence material with phosphorescence efficiency and lifetime up to 13.4%and 2.08 s through the simple host–guest doping strategy.Further on,by introducing the additional energy acceptor of fluorescein with concentration‐dependent emission to construct ternary doping systems,the afterglow color was extended from blue to yellow.Accordingly,the multicolor thermal printings have been easily realized,showing the great practical application prospects.

Efficient energy transfer in organic light-emitting transistor with tunable wavelength

Key challenges in the development of organic light-emitting transistors(OLETs)are blocking both scientific research and practical applications of these devices,e.g.,the absence of high-mobility emissive organic semiconductor materials,low device efficiency,and color tunability.Here,we report a novel device configuration called the energy transfer organic light-emitting transistor(ET-OLET)that is intended to overcome these challenges.An organic fluorescent dye-doped polymethyl methacrylate(PMMA)layer is inserted below the conventional high-mobility organic semiconductor layer in a single-component OLET to separate the functions of the charge transport and light-emitting layers,thus making the challenge to essentially integrate the high mobility and emissive functions within a single organic semiconductor in a conventional OLET or multilayer OLET unnecessary.In this architecture,there is little change in mobility,but the external quantum efficiency(EQE)of the ET-OLET is more than six times that of the conventional OLET because of the efficient Förster resonance energy transfer,which avoids exciton-charge annihilation.In addition,the emission color can be tuned from blue to white to green-yellow using the sourcedrain and gate voltages.The proposed structure is promising for use with electrically pumped organic lasers.

Color tunable and white light emitting via energy transfer in single-phase BiOCl:Er^(3+),Sm^(3+) phosphors for WLEDs

BiOCl crystal shows potential as efficient optical host due to its special layered structure. Here,the luminescence properties of the Er^3＋/Sm^3＋ co-doped BiOCl phosphors as single-phase phosphors were reported. Upon near ultraviolet excitation（NUV, 380 nm corresponding the ^4 I15/2→ ^4 G11/2 transition of Er^3＋ ions）, the phosphors exhibit the efficient characteristic emissions of Er^3＋ and Sm^3＋ ions simultaneously. The energy transfer（ET） from Er^3＋ to Sm^3＋ ions in the layered crystals has been validated by the variation of emission intensities and decay lifetimes respectively, which is ascribed to be a dipoledipole interaction. By virtue of the ET behavior and increasing Sm^3＋ ion concentration, the enhancing emission intensity of Sm^3＋ and the tunability of emission color from yellowish-green（0.318, 0.420） to white（0.343, 0.347） are realized. The results of our work indicate that the Er^3＋/Sm^3＋ co-doped BiOCI phosphor has a promising application serving as single component white emitting phosphors for NUV excited WLEDs.

Clustering-triggered phosphorescence of nonconventional luminophores

Nonconventional luminophores have attracted significant attention for their unique photophysical properties and potential applications in different areas.Unlike classic luminogens consisting of remarkably conjugated segments,nonconventional luminophores generally possess merely nonconjugated or short-conjugated structures based on electron-rich units.Fluorescence,phosphorescence,and even color tunable room temperature phosphorescence(RTP)could be readily obtained from these unique luminophores.Herein,we summarized recent advances in the phosphorescence of nonconventional luminophores,with focus on RTP and color tunable RTP.The clustering-triggered emission(CTE)mechanism could be applied to explain the luminescence as clustering-triggered phosphorescence(CTP).Furthermore,strategies toward the RTP regulation are summarized,and corresponding applications are demonstrated.

Digitally programmable organic light‐emitting tetrodes

Limited to the structure of traditional light‐emitting devices,electronic devices that can directly convert machine language into human visual information without introducing any back‐end circuit are still not easy to achieve.Based on a specially designed three‐phase co‐planar electrode structure,a new type of three‐phase alternating current driven organic light‐emitting device with the integration of emission and control functions,full‐color tunability and simple device structure is demonstrated in this study.We integrate the light‐emitting function of color‐tunable light‐emitting devices and the switching of three triodes in a single three phase organic light‐emitting device.The state control of luminous color and luminance intensity merely requires the introduction of a kind of machine language,that is an easy‐to‐program 6‐bit binary number coded digital signals.The color adjustable area covers 66%of the color triangle of the National Television System Committee.Such simple and easy‐to‐integrate light‐emitting system has great potential applications in the next‐generation man‐machine interface.

Design of a widely adjustable electrochromic device based on the reversible metal electrodeposition of Ag nanocylinders

Structural colors resulting from nanostructured metallic surfaces hold a series of advantages compared to conventional chemical pigments and dyes,such as enhanced durability,tunability,scalability,and low consumption,making them particularly promising for preparing color-tunable devices.However,once these structures are fabricated,they are almost all passive devices with static nanostructures and fixed optical properties,limiting their potential applications.Here,by using a specially designed array of ordered SiO2 nanoholes as a deposition template in conjunction with the traditional reversible metal electrodeposition device(RMED),we propose a tunable reflective surface where the color of the surface can be changed as a function of the thickness of the deposited Ag nanoparticles(AgNPs).Simplified manufacturability and a large range of color tunability are achieved over previous reports by utilizing the SiO2 nanohole template,which allows the direct deposition of AgNPs while forming an array structure of Ag nanocylinders.Besides,a further thematic analysis of the physical mechanism in the proposed structure is conducted.The results show that the structural colors induced by the longitudinal localized surface plasmon resonance(LSPR)mode can be dynamically tuned from brown to purple via increasing the deposition thickness.Additionally,in combination with SiO2 nanohole templates of varying parameters,a full gamut of colors spanning the entire visible spectrum is achieved,revealing the feasibility of utilizing the properties of the LSPR mode for satisfying various color requirements.We believe that this LSPRbased multicolor RMED design will contribute to the development of full color information displays and light-modulating devices.

Crystalline-State Solvent:Metal-Organic Frameworks as a Platform for Intercepting Aggregation-Caused Quenching

The sequestration of organic luminescent molecules(OLMs)within cage-based metal-organic frameworks(MOFs)as a dispersion platform has been developed to impede aggregation-caused quenching(ACQ).The homogenous encapsulation of distinct luminescent guests of different sizes and emissive behaviors in the cage structure of a MOF resulted in high fluorescent quantum yields of 44.8%for DAPI@NKU-110(DAPI=4',6-diamidino-2-phenylindole),65.4%for TPPA@NKU-110(TPPA=tris(4-(pyridin-4-yl)phenyl)amine),31.3%for R6G@NKU-110(R6G=Rhodamine 6G),and 58.3%for PY@NKU-110(PY=Pyronin Y),attributable to the confinement effect caused by the rigid cages of NKU-110.More significantly,a positive correlation of the encapsulated quantity of OLMs with their concentration in the in-situ solvothermal reaction was unveiled by spectral analysis and utilized to facilely fabricate a white-light-emitting crystal material TPPA+R6G@NKU-110.This material features a large crystal size on the millimeter-scale,broadband white emission,ideal CIE coordinates(0.33,0.34),and a high quantum yield(49.1%)when excited at 365 nm.Moreover,such a strategy can be easily generalized to an abundance of other cage-based MOFs and a plentiful volume of OLMs for the future development of colorful,high performance luminescent materials.

Highly sensitive color fine-tuning of diblock copolymeric nano-aggregates with tri-metallic cations,Eu(Ⅲ),Tb(Ⅲ),and Zn(Ⅱ),for flexible photoluminescence films(FPFs)

Luminescence materials have shown promise as display apparatus and lighting devices.The particularly interesting systems are photoluminescence materials that are capable of reversible colors emitting repeatedly on exposure to light.Here we report a series of color tunable flexible and transparent photoluminescence films consisting of multi-metals(Eu^(3+),Tb^(3+)and Zn^(3+))induced polymer aggregates(MIPAs)which are distributed uniformly in the polyacrylonitrile(PAN)films without agglomeration.MIPAs have a unique spherical structure due to the self-assembly of polystyrene-block-polyacrylic acid(PS-b-PAA)induced by metal ions.Notably,when applied in photoluminescence devices,these photoluminescence films exhibit not only red,green,blue colors(RGB)light,but also other tuned various color light covering the whole visible range upon excitation of 345 nm through adjusting the relative ratios of metal complexes.As the most important key point,non-conductive polymers can be used in photoluminescence devices as host medium,which is not realized in electroluminescent devices.Thus,the flexible photoluminescence films(FPFs)innovated herein exhibit the great potential to apply for flexible light-color and light-energy transformation devices.

An important step towards commercialization of quantum-dot light-emitting diode displays

Colloidal quantum dots(QDs)are a unique class of emissive materials with size-tunable emission wavelengths,saturated emission colors,near-unity luminance efficiency,inherent photo-and thermal-stability,and excellent solution processability.Display based on quantum-dot light-emitting diodes(QLED)may combine the superior properties of QDs,the benefits of solution-based fabrication techniques,and the advantages of self-emission devices,which promises an unprecedented generation of cost-effective,large-area,energysaving,wide-color-gamut,ultra-thin and flexible displays.