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Multicolor tunable upconversion nanoparticles (UCNPs) have garnered attention owing to their diverse applications such as displays, imaging, and security. Typically, achieving multicolor emission from UCNPs requires complicated core/multishell nanostructures comprising a core with at least five shells. Here, we propose a strategy to achieve bright and orthogonal red (R), green (G), and blue (B) upconversion (UC) luminescence without synthesizing complicated core/quintuple-shell or core/sextuple-shell nanostructures. For achieving bright and orthogonal RGB triprimary color UC luminescence, orthogonal bicolor-emitting core/shell-structured UCNPs are synthesized and blended. Orthogonal RB, RG, and GB luminescence are achieved through photon blocking. The combination of two orthogonal bicolor-emitting UCNPs exhibits pure RGB UC luminescence and full-color tunability via manipulation of excitation laser conditions. Furthermore, we present color displays achieved with transparent UCNP–polymer composites utilizing three distinct near-infrared light wavelengths, implying that the proposed strategy for attaining RGB UC luminescence may facilitate advancements in the development of full-color volumetric displays.

Extracellular matrix (ECM) undergoes dynamic inflation that dynamically changes ligand nanospacing but has not been explored. Here we utilize ECM-mimicking photocontrolled supramolecular ligand-tunable Azo+self-assembly composed of azobenzene derivatives (Azo+) stacked via cation-π interactions and stabilized with RGD ligand-bearing poly(acrylic acid). Near-infrared-upconverted-ultraviolet light induces cis-Azo+-mediated inflation that suppresses cation-π interactions, thereby inflating liganded self-assembly. This inflation increases nanospacing of “closely nanospaced” ligands from 1.8 nm to 2.6 nm and the surface area of liganded self-assembly that facilitate stem cell adhesion, mechanosensing, and differentiation both in vitroand in vivo, including the release of loaded molecules by destabilizing water bridges and hydrogen bonds between the Azo+molecules and loaded molecules. Conversely, visible light induces trans-Azo+formation that facilitates cation-π interactions, thereby deflating self-assembly with “closely nanospaced” ligands that inhibits stem cell adhesion, mechanosensing, and differentiation. In stark contrast, when ligand nanospacing increases from 8.7 nm to 12.2 nm via the inflation of self-assembly, the surface area of “distantly nanospaced” ligands increases, thereby suppressing stem cell adhesion, mechanosensing, and differentiation. Long-term in vivostability of self-assembly via real-time tracking and upconversion are verified. This tuning of ligand nanospacing can unravel dynamic ligand-cell interactions for stem cell-regulated tissue regeneration.

Herein, we demonstrate video-rate color three-dimensional (3D) volumetric displays using elemental-migration-assisted full-color-tunable upconversion nanoparticles (UCNPs). In the heavily doped NaErF4:Tm-based core@multishell UCNPs, erbium migration was observed. By tailoring this migration through adjustment of the intermediate shell thickness between the core and the sensitizer-doped second shell, red-green orthogonal upconversion luminescence (UCL) was achieved. Furthermore, highly efficient red-green-blue orthogonal UCL and full-color tunability were achieved in the UCNPs through a combination of elemental-migration-assisted color tuning and selective photon blocking. Finally, 3D volumetric displays were fabricated using a UCNP–polydimethylsiloxane composite. More specifically, 3D color images were created and motion pictures based on the expansion, rotation, and up/down movement of the displayed images were realized in the display matrix. Overall, our study provides new insights into upconversion color tuning and the achievement of motion pictures in the UCNP–polydimethylsiloxane composite is expected to accelerate the further development of solid-state full-color 3D volumetric displays.

Red, green, blue, and natural white upconversion (UC) luminescence colors are realized from the tetragonal-structured LiGdF4-based core/triple-shell (C/T-S) upconversion nanophosphors (UCNPs) and the C/T-S UCNP-incorporated polymer composites. The LiYF4:Yb cores are used as sensitized seeds for the formation of LiGdF4:Yb,Tm UC shell followed by the growth of LiGdF4:Tb,Eu color tuning shell. Finally, LiYF4inert shell is grown on the core/shell/shell UCNPs, and LiYF4:Yb/LiGdF4:Yb,Tm/LiGdF4:Tb,Eu/LiYF4C/T-S UCNPs exhibit enhanced UC luminescence. The single tetragonal-phased C/T-S UCNPs exhibit blue, green, and red UC luminescence, which is attributed to the electronic transitions in Tm3+via energy transfer UC process and Tb3+and Eu3+via energy migration UC process, respectively. The multicolor UC emissions, including natural white, medium aquamarine, purple, and thistle color, are created by fine-tuning of the ratio of Tb3+and Eu3+in the color tuning shell. The transparent polymer composites are prepared by incorporating the C/T-S UCNPs into polydimethylsiloxane, and the polymer composites also exhibit red, green, blue, and natural white light UC emissions, indicating that these multicolor tunable LiYF4:Yb/LiGdF4:Yb,Tm/LiGdF4:Tb,Eu/LiYF4C/T-S UCNPs have potential to be applied to transparent volumetric displays.

In this study, intense single-band red-emitting upconversion nanophosphors (UCNPs) excited with 800 nm near-infrared (NIR) light are reported. When a NaYF4:Nd,Yb active-shell is formed on the 12.7 nm sized NaGdF4:Yb,Ho,Ce UCNP core, the core/shell (C/S) UCNPs show tunable emission from green to red, depending on the Ce3+concentration under excitation with 800 nm NIR light. Ce3+-doped C/S UCNPs (30 mol %) exhibit single-band red emission peaking at 644 nm via a 5F5→ 5I8transition of Ho3+. A high Nd3+concentration in the shell results in strong absorption at around 800 nm NIR light, even though the shell thickness is not large, and small-sized C/S UCNPs (16.3 nm) emit bright red light under 800 nm excitation. The formation of a thin NaGdF4shell on the C/S UCNPs further enhances the upconversion (UC) luminescence and sub-20 nm sized core/double-shell (C/D-S) UCNPs exhibit 2.8 times stronger UC luminescence compared with C/S UCNPs. Owing to the strong UC luminescence intensity and Gd3+ions on the surface of nanocrystals, they can be applied as a UC luminescence imaging agent and a T1contrast agent for magnetic resonance (MR) imaging. In vivo UC luminescence and high-contrast MR images are successfully obtained by utilizing the red-emitting C/D-S UCNPs.

We synthesized uniform CuInS2/ZnS nanocubes by adjusting reaction parameters at the ZnS growth stage. Higher temperature and zinc concentration were shown to drive resultant crystals to have cubic morphology, which could be ascribed to the facet-dependent ligand dynamics on the crystal surface and concomitantly preferred directions of crystal growth. It was found that these nanocubes exhibit sensitive responses, as of photoluminescence quenching, toward hydrogen peroxide, compared to pyramid-shaped nanocrystals. The origin of quenching was further analyzed to be the oxidation of thiolate ligands that leaves the quenching center on the surface. It was noted that the quenched photoluminescence could be fully recovered by introducing additional ligand molecules into the system. Being adopted in the shape-controlled crystal growth, the ligand-to-crystal interaction was shown to still govern the interfacial reaction, the oxidation by hydrogen peroxide, of faceted crystals in our system. It turns out that the reactivity at the crystal surface depends on the exposed facets, especially induced by shape control, and the weak ligand-binding nature of the nanocube renders it vulnerable to the surface reaction.

Colloidal quantum dots (QDs) are attractive candidates for future lighting technology. However, in contrast to display applications, the realization of balanced white lighting devices remains conceptually challenging. Here, we demonstrate two-component white light-emitting QD-LEDs with high color rendering indices (CRI) up to 78. The implementation of orange CuInS2/ZnS (CIS/ZnS) QDs with a broad emission and high quantum yield together with blue ZnCdSe/ZnS QDs in a mixed approach allowed white light emission with low blue QD content. The devices reveal only a small color drift in a wide operation voltage range. The correlated color temperature (CCT) could be adjusted between 2200 and 7200 K (from warm white to cold white) by changing the volume ratio between orange and blue QDs (1:0.5 and 1:2).

The core/shell-structured upconversion nanophosphors (UCNPs) and Cd-free CuInS_2/ZnS quantum dots (QDs) were synthesized via coprecipitation and hot-injection methods, respectively, and they were applied to near infrared (NIR) photodetectors. The β-NaYF_4:Yb,Er/β-NaYF_4 UCNPs emitted intense visible light peaking at 522, 542, and 656 nm via H_11/22, S4_3/2, and F_9/24?I_15/24 transitions under excitation with 980 nm NIR light. The core/shell UCNPs showed 6.4 times higher emission intensity than core UCNPs. Charge carriers can be generated from CuInS_2/ZnS QDs in the QD-UCNP mixture due to their broad absorption in the visible spectral region shorter than 600 nm. The photodetector devices were fabricated by spin-coating CuInS_2/ZnS QDs on a SiO_2/Si substrate with patterned gold electrodes followed by spin-coating UCNPs on the QD layer. The fabricated QD-UCNP-bilayer-based device showed a drastically increased photocurrent (128 μA) compared with the QD-layer-based device under 980 nm NIR light illumination. Additionally, the fabricated device showed stable ON–OFF switching properties against on and off NIR light.

In this study, we report bright yellow-green-emitting CuInS2(CIS)-based quantum dots (QDs) and two-band white light-emitting diodes (LEDs) using them. To achieve high quantum efficiency (QE) of yellow-green-emitting CIS QDs, core/shell/shell strategy was introduced to high quality CIS cores (QE = 31.7%) synthesized by using metal–oleate precursors and 1-dodecanethiol. The CIS/ZnS/ZnS QDs showed a high QE of 80.0% and a peak wavelength of 559 nm under the excitation of 450 nm, which is well matched with dominant wavelength of blue LEDs. The formation of core/shell/shell structure was confirmed by X-ray diffraction, transmission electron microscopy, and inductively coupled plasma-optical emission spectroscopy analyses. Intense and broad yellow-green emission band of the CIS/ZnS/ZnS is beneficial for bright two-band white light. When the CIS/ZnS/ZnS was coated on the blue LEDs, the fabricated white LED showed bright natural white light (luminous efficacy (ηL) = 80.3 lm·W–1, color rendering index (Ra) = 73, correlated color temperature (Tc) = 6140 K). The QD–white LED package showed a high light conversion efficiency of 72.6%. In addition, the CIS/ZnS/ZnS-converted white LED showed relatively stable white light against the variation of forward bias currents of 20–150 mA [color coordinates (x, y) = (0.3320−0.3207, 0.2997−0.2867), Ra= 70–72, Tc= 5497–6375 K].

We report the unprecedented fabrication of a planar white lighting quantum dot light-emitting diode (QD-LED) through integrating a CdZnS QD-based blue electroluminescence (EL) device with a free-standing polymethyl methacrylate (PMMA) composite film embedded with orange-emitting Cu–In–S (CIS) green-greenish yellow-emitting Cu–In–Ga–S (CIGS) QDs. The hybrid device successfully generates bicolored white emission that comprises blue EL and downconverted QD photoluminescence. The hybrid QD-LEDs loaded with the composite film embedded with one type of QDs exhibit a limited white spectral coverage, consequently producing low values (<65) in color rendering index (CRI). Thus, the QD-PMMA film consisting of a blend of green CIGS and orange CIS QD downconverters is applied for obtaining a higher-CRI white light through the spectral extension, resulting in a much improved CRI of 75–77. Various EL performances of the hybrid planar white device versus the reference blue QD-LED are also characterized in details.

Novel pH-responsive assemblies (PEG-lipid:DOPE liposomes) containing tunable and bifunctional phenyl-substituted vinyl ether (PIVE) cross-linkers were prepared. The assemblies consisted of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), acid-cleavable poly(ethylene glycol) (PEG)-conjugated lipids, pDNA, and protamine sulfate (PS). The PIVE linkage was designed to hydrolyze under acidic conditions, and the hydrolysis studies of PEG-lipid compounds containing PIVE at pH 4.2, 5.4, and 7.4 indicated that the hydrolysis rates of PIVE linker were influenced by the substitution of electron withdrawing or electron donating groups on the phenyl ring. Acid-catalyzed hydrolysis of PIVE leads to destabilization of the acid labile PEG-PIVE-lipid:DOPE liposomes via dePEGylation, thereby triggering content release. Content release assays showed that dePEGylation was highly pH-dependent and correlated with the PIVE proton affinity of the phenyl group. These results indicated that the dePEGylative triggering based on a new pH-sensitive PIVE linkage can be controlled. In vitro transfection studies on the pH-responsive assemblies containing mPEG-(MeO-PIVE)-conjugated 1,3-dioctadecyl-rac-glycerol lipids (mPEG-(MeO-PIVE])-DOG) showed higher transfection efficiency compared to that of polyethylenimine (PEI), a positive control, on HEK 293 and COS-7 cells. In addition, lower cytotoxicity of PEG-PIVE-lipid:DOPE liposomes/PS/DNA was observed in comparison to PEI. These results suggest that PEG-PIVE-lipid:DOPE liposomes can be considered as nonviral vehicles for drug and gene delivery applications.

Here, excitation orthogonalized red/green/blue upconversion luminescence (UCL)-based full-color tunable rare-earth (RE) ion-doped upconversion nanophosphors (UCNPs) are reported. The LiREF4-based core/sextuple-shell (C/6S) UCNPs are synthesized, and they consist of a blue-emitting core, green-emitting inner shell, and red-emitting outer shell, with inert intermediate and outermost shells. The synthesized C/6S UCNPs emit blue, green, and red light under 980, 800, and 1532 nm, respectively. Importantly, by combining incident near-infrared (NIR) light with various wavelengths (800, 980, and 1532 nm), full-color UCL including blue, cyan, green, yellow, orange, red, purple, and white UCL is achieved from the single C/6S UCNP composition. The color gamut obtained from the C/6S UCNPs shows 101.6% of the sRGB standard color gamut. Furthermore, transparent C/6S UCNP-polydimethylsiloxane (PDMS) composite is prepared. Full-color display realized in the transparent C/6S UCNP-PDMS composite indicates the feasibility of constructing the C/6S UCNP-based three-dimensional volumetric displays with wide color gamut.

High-power white light-emitting diodes (LEDs) are fabricated by combining blue LEDs and green (Ba,Sr)_2SiO_4:Eu^2+ and red CaAlSiN_3:Eu^2+ phosphors with varying phosphor geometry. The white LED having separated the phosphor layer by the silicone gel layer between green and red phosphor layers shows superior optical properties. The luminous efficiency (η_L) is improved by a decrease of reabsorption of green light by red phosphor owing to a difference among refractive indices. The white LED shows very high η_L of 51 lm/W and a high color rendering index of 95 under 350 mA. In addition, improved luminous properties of the white LED including a separated phosphor layer are confirmed via ray-trace simulation.

A yellow-emitting Tb_3Al_5O_12:Ce^3+ (TAG:Ce) phosphor was coated on blue light-emitting diodes (LEDs) to obtain white LEDs (WLEDs). Since TAG:Ce showed 90% of the brightness of Y_3Al_5O_12:Ce^3+ (YAG:Ce), it was expected that TAG:Ce-based WLEDs showed 90% of brightness of YAG:Ce-based ones. However, the TAG:Ce-based WLED showed 74% of the brightness of YAG:Ce-based one. Considering the density and size of the phosphors, the higher density and larger size of TAG:Ce induced a great deal of sedimentation of TAG:Ce particles in an epoxy resin. It is believed that this is one of main reasons for the reduced optical power of the TAG:Ce-based WLED compared to that of the WLED expected from the brightness of TAG:Ce.

White-light-emitting diodes (WLEDs) were fabricated by combining a yellow Sr_3SiO_5:Ce^3+, Li^+ phosphor with a blue light-emitting diode (LED) (460 nm chip) or a near ultraviolet (n-UV) LED (405 nm chip), respectively. Color temperature (T_c) of Sr_3SiO_5:Ce^3+, Li^+-based WLEDs could be tuned from 6500 to 100,000 K (blue LED pumping) and from 4900 to 50,000 K (n-UV LED pumping) without mixing with other phosphors. The blue LED-pumped WLED showed excellent white light (luminous efficiency=31.7 lm/W, T_c=6857 K) at 20 mA. This WLED showed a stable color coordinates property against an increase of the forward current. An n-UV LED-pumped WLED also showed bright white light (25.0 lm/W, 5784 K) at 20 mA.

La0.827Al11.9O19.09:Eu2+,Mn2+(LAO:Eu,Mn) was prepared for ultraviolet light-emitting diodes (UV LEDs) application. LAO has a distorted magnetoplumbite structure which can provide 12-coordinated site for an La ion and two different sites for Al ions, tetrahedral and octahedral sites. Co-activators, Eu and Mn, were substituted for La site and Al sites of LAO, respectively. The LAO:Eu,Mn phosphor has three emission bands composed of blue, green, and red, and emitting colors can be controlled from blue to red by manipulating concentration of the activators. The energy transfer mechanism among lanthanide ions in the phosphor was investigated by photoluminescence and electron paramagnetic resonance techniques. The energy transfer from Eu to Mn was revealed to occur via dipole-quadrupole interaction. The critical distance for the energy transfer was calculated to be about 9 Å by two methods. In addition, efficient multi-color LEDs were fabricated by LAO:Eu,Mn phosphors showing multi-color luminescence.

Thiol-capped CuInS2-ZnS core-shell quantum dot (QD) embedded in silica powder is synthesized by in situapproach, which contributes to facileness, high reproducibility and mass-productivity. The proposed method is distinguished in that it uses intermediate ligand-exchange step with hydroxyl-terminated ligands during growth stage, which helps the QDs to be dispersed in polar silane matrix to form micron-sized silica powder. This results in well-dispersed QDs in the silica powder with luminescence efficiency of 34%. In addition, the QDs/silica composites are applied to white-LEDs, demonstrating high quality white light with high color stability under various operating currents.

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The luminescence properties of orange-yellow-emitting Eu2+-activated Sr3SiO5were optimized for application to blue/near ultraviolet (n-UV) light-emitting diodes (LEDs). Sr2.97SiO5:Eu0.032+showed strong orange-yellow emission peaking at ∼580nmunder blue and n-UV light of 450 and 405nm, respectively, and the effects of Ca and Ba substitutions into Sr2+sites on the emission band change were investigated. For the substitution of Ca, Ca3SiO5:Eu2+showed no orange-yellow emission under blue light due to the different crystal structures of Ca3SiO5(monoclinic) and Sr3SiO5(tetragonal). The redshift and blueshift of the emission band of (Sr1−xBax)3SiO5:Eu2+were explained by the competition between crystal field effect and Nephelauxetic effect. The 460nm-emitting blue LED-pumped white LED with Sr3SiO5:Eu2+or a mixture of Sr3SiO5:Eu2+and green phosphor (Ba2SiO4:Eu2+)were fabricated and they showed color coordinates of (0.343, 0.281) and (0.349, 0.339), respectively.

A red-emitting LiLa2O2BO3:Sm3+,Eu3+phosphor has been synthesized and characterized optically for white light-emitting diodes (LEDs). Because the oxyborate group (O2BO3−7)can contain high Eu3+concentration without concentration quenching, LiLa2O2BO3is a suitable host material for red-emitting phosphor for near-ultraviolet (n-UV) LEDs. When LiLa2O2BO3:Eu3+was co-doped with Sm3+, emission intensity of Eu3+was enhanced by ∼30%than that of the sample without Sm3+owing to the energy transfer from Sm3+to Eu3+. This energy transfer was confirmed by faster decay times of Sm3+as energy donors. LiLa2O2BO3:Sm3+,Eu3+showed a relative brightness of 334.7% of that of Y2O2S:Eu3+, commercial red-emitting phosphor for n-UV LEDs.