Tunable White Light Emission Research Articles

PMMA-copolymerized color tunable and pure white-light emitting Eu3+–Tb3+containing Ln-metallopolymers

Homo or hetero Ln-metallopolymers with tunable multicoloured and white light emission were fabricated by anchoring lanthanide coordination monomers onto PMMA backboneviapre-designed vinylbenzyl-substituted NTB-type ligand.

Designing of blue, green, and red CsPbX3 perovskite-codoped flexible films with water resistant property and elimination of anion-exchange for tunable white light emission.

We successfully synthesized blue, green, and red CsPbX3 QDs-codoped flexible films using a one-step electrospun strategy, followed by coating a strongly hydrophobic silicone resin on the surface of the films. The codoped flexible light-emitting films are resistant to water, thereby preventing anion exchange and significantly prolonging the lifetime of light emitters under ambient air conditions.

Tunable white light emission from a single-host phosphor Gd2MoO6:Eu3+,Dy3+ for near ultraviolet light-emitting diodes

Abstract

A white-light emitting phosphor LuNbO4:Dy3+ with tunable emission color manipulated by energy transfer from [formula omitted] groups to Dy3+

A single-phase white-light emitting phosphor LuNbO4:Dy3+ was synthesized using the solid state method in air for the first time. X-ray diffraction (XRD) along with excitation spectra, emission spectra, decay times and thermal stability were exploited to characterize the asprepared phosphors. Under ultraviolet (UV) excitation (261nm), the self-activated emission of the LuNbO4 host is peaked at 402nm with a broad emission band ranging from 320nm to 600nm, ascribing to the charge transfer in NbO43− groups, which has spectral overlapping to the excitation of f–f transitions of Dy3+ in LuNbO4:Dy3+ phosphors. They show both the broad host emission and sharp emission lines due to the characteristic f–f transitions of Dy3+ ions, which exhibit tunable white light emissions due to the energy transfer from the NbO43− groups in the host to Dy3+ with increased Dy3+ content. The optimal chromaticity coordinates and Correlated Color Temperature (CCT) in LuNbO4:Dy3+ are (x=0.336, y=0.311) and 5299K, respectively, which occur when the doping Dy3+ is 0.01. The decrease of decay lifetime for host emission in LuNbO4:Dy3+ with raised Dy3+ content demonstrates the energy transfer from the host to Dy3+. The energy transfer mechanism in LuNbO4:Dy3+ phosphors was determined to be a resonant type via dipole–dipole mechanism. Moreover, good thermal stability was also identified in Lu0.99NbO4:0.01Dy3+ and its emission intensity was reduce to 85% of its initial value at 100°C and 62% at 200°C, the chromaticity color coordinate values of Lu0.99NbO4:0.01Dy3+ had a slight shift with raised temperature. The current research suggests that LuNbO4:Dy3+ could potentially serve as a single-phase white-light emitting phosphor in solid-state lighting and display fields.

Optical Properties and White Emission from Dy<sup>3+</sup> Doped in Y<sub>2</sub>O<sub>3</sub>-CaO-SiO<sub>2</sub>-B<sub>2</sub>O<sub>3</sub> Glasses

The Dy3+ doped Y2O3-CaO-SiO2-B2O3 glasses with molar composition 25Y2O3 : 10CaO : 10SiO2 : (55-x)B2O3, where x is 0.0 to 0.5 mol%, have been prepared by melt quenching method and are characterized through absorption, photoluminescence and decay analysis. From the luminescent spectra, observed a strong yellow and blue emission from 4F9/2→ 6H13/2 (575 nm) and 4F9/2 → 6H15/2 (482 nm) transition of Dy3+ ions respectively. The tunable white light emission at different excitation wavelengths are investigated through CIE 1931 diagram. The decay curves show the decreasing of lifetimes when addition of Dy2O3 concentration.

Adjustable white-light emission from a photo-structured micro-OLED array.

White organic light-emitting diodes (OLEDs) are promising candidates for future solid-state lighting applications and backplane illumination in large-area displays. One very specific feature of OLEDs, which is currently gaining momentum, is that they can enable tunable white light emission. This feature is conventionally realized either through the vertical stacking of independent OLEDs emitting different colors or in lateral arrangement of OLEDs. The vertical design is optically difficult to optimize and often results in efficiency compromises between the units. In contrast, the lateral concept introduces severe area losses to dark regions between the subunits, which requires a significantly larger overall device area to achieve equal brightness. Here we demonstrate a color-tunable, two-color OLED device realized by side-by-side alignment of yellow and blue p-i-n OLEDs structured down to 20 μm by a simple and up-scalable orthogonal photolithography technique. This layout eliminates the problems of conventional lateral approaches by utilizing all area for light emission. The corresponding emission of the photo-patterned two-unit OLED can be tuned over a wide range from yellow to white to blue colors. The independent control of the different units allows the desired overall spectrum to be set at any given brightness level. Operated as a white light source, the microstructured OLED reaches a luminous efficacy of 13 lm W−1 at 1000 cd m−2 without an additional light outcoupling enhancement and reaches a color rendering index of 68 when operated near the color point E. Finally, we demonstrate an improved device lifetime by means of size variation of the subunits.

W-shaped 1,3-di(2,4-dicarboxyphenyl)benzene based lanthanide coordination polymers with tunable white light emission

A series of trinuclear LnCPs with unprecedented (3,8)-connected 3D (4.52)2(42.512.66.75.83) architectures were synthesized. White light emission was realized by the Eu(iii)-doped Dy(iii) complexes.

Assembly of one-, two-, and three-dimensional Ln(iii) complexes constructed from a novel asymmetric tricarboxylic acid: synthesis, structure, photoluminescence and tunable white-light emission

By reacting an asymmetric semi-rigid V-shaped linker H3dpob (H3dpob = 3-(2′3′-dicarboxylphenoxy)benzoic acid) and Ln(NO3)3·6H2O, nine novel Ln-based luminescent materials, from 1D to 3D, namely {[Eu(dpob)(phen)]·H2O}n (1), {[Ln(Hdpob)(ox)0.5(H2O)2]}n (Ln = Eu(2), Sm(3), Gd(4), Tb(5)), {[Eu(dpob)(H2O)2]·0.5H2O}n (6), and {[Ln(dpob)(H2O)2]·mH2O}n (Ln = Eu(7), Gd(8), Tb(9), m = 0.5 for 7 and 9; m = 1 for 8) (phen = 1,10-phenanthroline; H2ox = oxalic acid) have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction, infrared (IR) spectroscopy, elemental analysis, and PXRD. The crystal structures of 1–9 indicate that the coordination modes and coordination configuration of the H3dpob ligand play critical roles in the formation of the lanthanide architectures. Complexes 1–5 display multiple structures from double-stranded 1D chains to 4-connected 2D layers, through [Eu2(CO2)4] or [Eu2(CO2)2] dinuclear units with different auxiliary ligands. Complexes 6 and 7 are genuine supramolecular isomers which are induced by the concentration effect. 6 possesses a 2D kgd network with a Schlafli symbol of (43)2(46·66·83) built from 6-connected [Eu2(CO2)2] units and 3-connected H3dpob, which further connects to a (3,8)-connected tfz-d topology through O–H⋯O hydrogen bonds. 7 displays a 3D (3,6)-connected rtl network with the Schlafli symbol (4·62)2(42·610·83). Eu complexes 1, 2, 6, and 7 as well as Tb complexes 5 and 9 could provide intense and bright characteristic 5D0 → 7FJ/5D4 → 7FJ red/green luminescence under UV excitation in the solid state at 298 K and 77 K. The calculated singlet and triplet energies of H3dpob as well as phen and H2ox ligands indicate that these ligands act as antenna chromophores that are able to efficiently absorb and transfer energy to Ln(III) ions. In complexes 1, 2 and 5, ligand-to-metal energy transfer processes could occur in mixed ligands. However, these processes occurred in a single H3dpob ligand in complexes 6 and 7. With careful adjustment of the relative concentration of the lanthanide ions and by varying the excitation wavelengths of {[Gd0.92Eu0.04Tb0.04(dpob)(H2O)2]·0.5H2O}n (10), tunable yellow (CIE coordinate: 0.51, 0.40) to white-light (CIE coordinate: 0.33, 0.34) emission has been obtained.

Highly thermostable lanthanide(iii) MOFs constructed from 4,4′,4′′-s-triazine-2,4,6-triyl-tribenzoate ligand: synthesis, structure, and tunable white-light emission

A series of highly thermally stable lanthanide metal–organic frameworks formulated as [Ln2(TATB)2(DMSO)6]·DMF·DMSO·H2O [Ln = La (1), Ce (2), Pr (3), Sm (4), Eu (5)] and [Ln2(TATB)2(DMSO)5(CH3OH)]·DMF·DMSO·2H2O [Ln = Nd (6), Gd (7), Tb (8)] (TATB3− = 4,4′,4′′-s-triazine-2,4,6-triyl-tribenzoate, DMF = N,N-dimethylformamide and DMSO = dimethylsulfoxide) have been successfully synthesized under solvothermal conditions and characterized by single crystal X-ray diffraction, infrared (IR) spectroscopy, elemental analysis, thermogravimetric analyses (TGA) and powder X-ray diffraction (PXRD). Single crystal X-ray diffraction analysis reveals that all of the compounds are isomorphous, crystallize in the triclinic space group 1 and exhibit two-dimensional (2D) (3,3)-connected layered structures with the Schlafli symbol {63}. Solid-state photoluminescence measurement illustrates that compounds 5 and 8 exhibit remarkable red and green luminescence emissions with lifetimes at the millisecond scale, respectively, while complexes 3, 4, and 6 display characteristic luminescence emissions in the near-infrared region. With careful adjustment of the relative concentration of the doping Eu3+ and Tb3+ ions in the La3+ complex, the color of the luminescence can be modulated, and white-light emitting materials can be successfully obtained.

Tunable multicolor luminescence and white light emission realized in Eu3+ mono-activated GdF3 nanofibers with paramagnetic performance

GdF3:Eu3+ nanofibers with luminescent–magnetic bi-functionality have been successfully fabricated by combination of electrospinning followed by subsequent calcination with fluorination technology.

Tunable luminescence and white light emission of mixed lanthanide–organic frameworks based on polycarboxylate ligands

This review highlights the luminescence tuning and white light emission of aromatic polycarboxylate-based mixed Ln-MOFs by changing the relative concentration of the constituent Ln3+ ions or the excitation wavelength.

Synthesis, structure, and tunable white light emission of heteronuclear Zn2Ln2 arrays using a zinc complex as ligand

White light emission was realized by codoping Eu(iii) ion in the Dy(iii) complex for the first time.

Micro-crystals of metal–organic frameworks constructed from pyrene-based organic linkers and lanthanide ions for tunable white light emission

A series of micro-sized luminescent crystals of metal–organic frameworks are synthesized from pyrene-based organic linkers and lanthanide ions. The emission color of the micro-crystals is rationally controlled and white-light-emitting micro-crystals are achieved by adjusting the amounts of components (organic linkers and lanthanide ions) and the excitation wavelength.

Liquid-Phase Epitaxy Effective Encapsulation of Lanthanide Coordination Compounds into MOF Film with Homogeneous and Tunable White-Light Emission.

As a new family of hybrid inorganic-organic materials with large porosity, metal-organic frameworks (MOFs) have received attractive attention recently on encapsulating functional guest species. Although the encapsulation of luminescent guest into bulk MOFs can tune the luminescent property, the powder composite materials are limited to the application in optical sensors and devices. In the present work, we use a modified liquid-phase epitaxial (LPE) pump method for the fabrication of lanthanide coordination compounds (LCCs)-encapsulated MOF thin film on substrate with high encapsulation efficiency. The resultant composite film reveals an oriented and homogeneous composite film, in which a white light emission by tuning the LCCs of red, blue and green emission can be obtained. This strategy may open new perspectives for developing high-encapsulation-efficiency, oriented, and homogeneous solid-state lighting composite films in the application of optical sensors and devices.

Dual energy transfers and color tunable emission in Eu2+/Tb3+/Mn2+-triactivated Mg21Ca4Na4(PO4)18 phosphors

A series of single-composition Mg21Ca4Na4(PO4)18: Eu2+,Tb3+,Mn2+ phosphors have been synthesized via a combustion-assisted synthesis technique. The crystal structure, luminescence properties, and energy transfers (ET) from Eu2+ to Tb3+ and/or Mn2+ ions are discussed in detail. The ETEu–Tb and ETEu–Mn processes in the Mg21Ca4Na4(PO4)18 host are demonstrated to be resonant types via dipole–dipole interaction and quadrupole–quadrupole interaction, respectively. Additionally, the emitting colors of Mg21Ca4Na4(PO4)18: Eu2+, Tb3+, Mn2+ samples can be tuned from blue to blue–green via the ETEu–Tb process and from blue to reddish purple via the ETEu–Mn process. Finally, the tunable white light emission with high quantum yields (>50%) was realized by precise control of the concentrations of Eu2+, Tb3+, and Mn2+ ions. The results suggest the developed phosphors can find applications in the field of ultraviolet irradiation pumped white-LEDs.

Microwave-assisted aqueous synthesis of transition metal ions doped ZnSe/ZnS core/shell quantum dots with tunable white-light emission

Synthesis of bright white-light emitting Mn and Cu co-doped ZnSe/ZnS core/shell quantum dots (QDs) (Cu,Mn:ZnSe/ZnS) was reported. Water-soluble ZnSe-based QDs with Mn and Cu doping were prepared using a versatile hot-injection method in aqueous solution with a microwave-assisted approach. Influence of the Se/S ratio, stabilizer, refluxing time and the concentration of Cu/Mn dopant ions on the particle size and photoluminescence (PL) were investigated. The as-prepared QDs in the different stages of growth were characterized by X-ray powder diffractometer (XRD), high-resolution transmission electron microscopy (HRTEM), UV–visible (UV–vis) spectrophotometer, and fluorescence spectrophotometer. It is found that these ZnSe-based QDs synthesized under mild conditions exhibit emission in the range of 390–585nm. The PL quantum yield (QY) of the as-prepared water-soluble ZnSe QDs can be up to 24.3% after the UV-irradiation treatment. The band-gap emission of ZnSe is effectively restrained through Mn and Cu doping. The refluxing time influences the doping of not only Mn, but also Cu, which leads to the best refluxing time of Mn:ZnSe and the red-shift of the emission of Cu:ZnSe d-dots. Co-doping induced white-light emission (WLE) from Cu,Mn:ZnSe/ZnS core/shell QDs were obtained, which can offer the opportunity for future-generation white-light emitting diodes (LEDs).

Tunable white light emission by variation of composition and defects of electrospun Al2O3-SiO2 nanofibers.

Composite nanofibers consisting of Al2O3–SiO2 were prepared by electrospinning in combination with post-calcination in air. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used to investigate the crystalline phase and microstructure of the composite nanofibers. Photoluminescence experiments indicated that the resulting white light emission can be tuned by the relative intensity of the individual spectral components, which are related to the individual defects such as: violet-blue emission from O defects, green emission from ≡Si(Al)–O–C∙=O, and red emission from intersystem radiative crossing. White light emission was realized at a Al/(Al–Si) ratio of 40 and 60 mol %. This research may offer a deeper understanding of the preparation of efficient and environmentally friendly, white luminescence materials.

Hybrid ZnO-Based Nanoconjugate for Efficient and Sustainable White Light Generation

Developing new ways of generating white light is of paramount importance for the design of the next generation of smart, energy-efficient lighting sources. Here we report tunable white light emission of hybrid organic–inorganic nanostructures based on colloidal ZnO nanocrystals conjugated with organic fluorophores. These materials act as single nanophosphors owing to the distance-dependent energy transfer between the two components. The defect-based size-tunable ZnO nanocrystal blue-green emission coupled with complementary color emission from different fluorophores allows for the generation of white light with targeted chromaticity, color temperature, and color rendering index. We further show that silane layer-protected nanoconjugates result in increased stability of white light emission over a long period of time. The results of this work demonstrate an inexpensive, green, and sustainable approach to general solid-state lighting, without the use of rare earth or heavy metals. Colloidal form of the repo...

Multichromophoric organic molecules encapsulated in polymer nanoparticles for artificial light harvesting.

We designed a self-assembled multichromophoric organic molecular arrangement inside polymer nanoparticles for light-harvesting antenna materials. The self-assembled molecular arrangement of quaterthiophene molecules was found to be an efficient light-absorbing antenna material, followed by energy transfer to Nile red (NR) dye molecules, which was confined in polymer nanoparticles. The efficiency of the antenna effect was found to be 3.2 and the effective molar extinction coefficient of acceptor dye molecules was found to be enhanced, which indicates an efficient light-harvesting system. Based on this energy-transfer process, tunable photo emission and white light emission has been generated with 14 % quantum yield. Such self-assembled oligothiophene-NR systems encapsulated in polymer nanoparticles may open up new possibilities for fabrication of artificial light harvesting system.

Tunable white-light emission via energy transfer in single-phase LiGd(WO4)2:Re3+ (Re = Tm, Tb, Dy, Eu) phosphors for UV-excited WLEDs

Novel single-phase white-light-emitting phosphors have been successfully synthesized by a solid-state reaction and their photoluminescence properties and energy transfer mechanism have been carefully investigated.