Tunable White Light Emission Research Articles

Two dye-encapsulated triple-emitting naphthalene-based Zr-MOFs for tunable white-light emission and dual mode detection of inorganic ions

A dual-dyes-encapsulated white-light emitting naphthalene-based Zr-MOF was synthesized and employed as fluorescent sensor for detecting inorganic ions with quenching or colorimetric detection mode.

Tunable warm white light emission and energy transfer of Dy3+ co-doped Sr2 LaZrO5.5 :Eu3+ phosphors.

Eu3+ ,Dy3+ co-doped Sr2 LaZrO5.5 -based phosphors were prepared through a sol-gel method. Through characterization, it was found that the Sr2 LaZrO5.5 -based fluorescent powder co-doped with Eu3+ and Dy3+ had a cubic structure. At an excitation wavelength of 290 nm, the substrate Sr2 LaZrO5.5 exhibited strong blue emission at 468 nm, and the Sr2 LaZrO5.5 :18%Eu3+ phosphor exhibited a strong red emission peak at 612 nm. When the doping amount of Dy3+ was 5, 8, 12, 15, or 18%, the Sr2 LaZrO5.5 :18%Eu3+ phosphor changed from an orange-red light, to a warm white light, and to a cold white light. According to the emission spectra, the emission intensities of the substrates Sr2 LaZrO5.5 and Sr2 LaZrO5.5 :Eu3+ decreased with increasing Dy3+ concentration, confirming the energy transfer between the host Sr2 LaZrO5.5 -Eu3+ ,Dy3+ , and resulting in a lower CCT value, with significantly improved white light emission.

Antimony-Triggered Tunable White Light Emission in Lead-Free Zero-Dimensional Indium Halide with Ultrastable CCT of White Light Emitting Diodes.

A highly efficient and easily tunable luminescence is significant for solid-state luminescent (SSL) materials. However, achieving a photoluminescence quantum yield (PLQY) close to unity and tuning the emission remain challenging tasks. Metal doping strategies enable resolution of these issues. Herein, we report the preparation of a novel organic-inorganic lead-free indium-based metal halide hybrid (MP)3InCl6•EtOH (MP = C4H10ON) with a typical zero-dimension structure. When excited at 320 nm, (MP)3InCl6•EtOH exhibits a dual emission band at 420 and 600 nm, which originates from the organic cation [MP] and the [InCl6]3- octahedral unit. The photoluminescence can be significantly enhanced through Sb3+ doping, resulting in an increase in PLQY from 0.78% to near unity. Multiple emission color tunings have been achieved by regulating the Sb doping level and the radiation wavelength, resulting in a change in emission color from blue → white → orange. Optical characterizations reveal that the significantly enhanced emission centered at 600 nm can be attributed to more efficient absorption, closely associated with an additional 1S0 → 3P1 transition in the inorganic octahedron [In(Sb)Cl6]3- due to Sb3+ doping. With its excellent optical performance, a white light emitting diode (WLED) has been successfully fabricated by coating the mixture of (MP)3InCl6•EtOH:15%Sb3+ with blue phosphor BaMgAl10O17:Eu2+ onto a UV LED chip. The WLED device exhibits perfect white light emission with regard to the International Commission on Illumination (CIE) coordinates of (0.36, 0.34). Significantly, the WLED device maintains a stable correlated color temperature (CCT) range of 4119-4393 K and CIE coordinates (x: 0.37-0.34, y: 0.35-0.33) as the driven current varies from 20 to 200 mA, demonstrating outstanding stability across different power levels. This work not only presents a novel system for achieving remarkably enhanced luminescent performance and tuning emission bands in 0D metal halides but also represents a significant step toward achieving resistance to color drifting for stable WLEDs.

Pb2+/Mn2+ co-doped Cs2ZnBr4 microcrystals with dual-band tunable white light emission

The photoelectric properties of lead halide perovskite have been extensively investigated. However, its application in the field is greatly limited due to its poor instability and high lead content. With the aim of addressing these problems, in this study, Cs2ZnBr4:Pb2+/Mn2+ microcrystals were initially synthesized using a simple precipitation method. By manipulating the lead concentration, the emission ranging from cyan to green could be adjusted in Cs2ZnBr4:Pb2+. Co-doped Cs2ZnBr4:Pb2+/Mn2+ microcrystals with the precise regulation of the doping concentration of Pb2+ and Mn2+ were obtained through precipitation. The dual-mode emission of cyan and orange-red is successfully obtained. It is important that single white light emission is achieved in Cs2ZnBr4:Pb2+/Mn2+ microcrystals, exhibiting tunability from cold white to warm white. Moreover, Cs2ZnBr4:Pb2+/Mn2+ microcrystals are demonstrated remarkable air stability: it retains 86.27 % of the initial fluorescence intensity after 45 days in ambient conditions; it exhibits excellent UV stability, with 88.3 % of the initial fluorescence intensity maintained even after nearly 30 h of ultraviolet irradiation. Therefore, this research is anticipated to have broad applications not only in the field of solid-state lighting as UV-excited white LEDs but also in serving as a valuable reference for the exploration of low-lead halide luminescent materials.

Assembly of One-, Two-, and Three-Dimensional Cu(I)-Based Coordination Frameworks for Tunable White Light Emission and Effective Fluorescence Sensing

Assembly of One-, Two-, and Three-Dimensional Cu(I)-Based Coordination Frameworks for Tunable White Light Emission and Effective Fluorescence Sensing

Structure and tunable white-light emission of the Ce3+/Dy3+ co-doped MgO–K2O–B2O3–P2O5 borophosphate glasses by modulating Mg/K ratio

In this work, the Ce3+/Dy3+ co-doped MgO–K2O–B2O3–P2O5 borophosphate glasses were successfully fabricated by the melt-quenching technique. The structure and optical characteristics were investigated using XRD, DSC, FTIR, Raman spectra, transmittance spectra and photoluminescence (PL) spectra. With increasing Mg/K ratio, the free oxygen introduced by MgO as its contents increase facilitated the conversion of [BO3] triangular units to the denser [BO4] tetrahedral units. The phonon energy of the glass system was estimated to be about 1020 cm−1 from the Raman spectra. Spectroscopic analysis revealed the energy transfer (ET) between Ce3+ and Dy3+ may exist, and the ET between Ce3+ and Dy3+ was explored in detail. Under 315 and 349 nm excitation, the PL spectra disclosed three distinct emission peaks at about 370, 484, and 575 nm, which corresponded to the 5d-4f (Ce3+), 4F9/2 → 6H15/2 (Dy3+), and 4F9/2 → 6H13/2 transitions (Dy3+), respectively. The blue shift in the peak position of the cerium ions within the excitation and emission spectra was associated with the decrease in the overall optical basicity of the glass caused by compositional modulation. Tunable white light emission can be achieved by varying the excitation wavelength. Under 349 nm excitation, the optimum chromaticity coordinate (0.325, 0.333) with a correlated color temperature value of 5856 K is obtained at the Mg/K ratio of 3:2, which points to the Ce3+/Dy3+ co-doped MgO–K2O–B2O3–P2O5 borophosphate glasses are a prospective fluorescent material for exploitation of white light-emitting diodes (WLEDs).

Dual emitting carbon nanoparticles for tunable white light emission

Eco-friendly, biomass derived single component luminescent materials with dual emission bands hold immense potential in white light emitting devices (WLED). Compared to WLED fabricated from different color emitting carbon nanoparticles, self-reabsorption and degradation will be negligible in single system white light emitting materials which guarantees stability in long run. Herein, we report a facile, inexpensive and sustainable direct thermal decomposition method to synthesize carbon nanoparticles with dual emission bands. Addition of PVP could efficiently enhance the red emission band of carbon nanoparticles. The excitation dependent broad blue-green emission and excitation independent narrow red emission helps to obtain white light emitting carbon nanoparticles. Upon change in excitation wavelength from 410 nm to 370 nm, white light emissions are obtained with tunable CCT value from 2648 K to 8980 K respectively. By virtue of this tunable warm to cool white light emission, single system WLED can be designed suitable for both indoor and outdoor applications.

Full-spectrum and tunable white light emission of germanate glass-ceramic containing defective Zn2GeO4 and Mn2+ ions

The full-spectrum phosphors are key components for improving the light quality of phosphor-converted white light-emitting diodes (pc-WLEDs). In this work, a novel germanate glass-ceramic (GC) doped with Mn2+ was developed to achieve full-spectrum white light emission deriving from the defective Zn2GeO4 crystalline phase and Mn2+ with multisite occupancy. The defective Zn2GeO4 is crystallized in situ from the well-designed precursor germanate glass by a controllable heat treatment. The energy states of intrinsic defects, including oxygen and zinc vacancies and interstitial zinc and oxygen of Zn2GeO4 in GC, have been studied by first-principles calculations. The luminescence property and the energy transfer mechanism between the defect states and Mn2+ ions in the GC material was proposed. Under the UV excitation, the luminescence property can be tuned by adjusting the distribution of Mn2+ ions in between the glassy and crystalline phases. The correlated color temperature (CCT) and color rendering index (CRI) of the UV-excited full-spectrum white light emission can be tuned over a wide range. This combinatorial strategy of intrinsic defects and multisite ion doping for full-spectrum white light emission in GC, which overcomes the limitation of conventional discontinuous white light emitting materials that emit singly from doping ions, has shown good potential for application in pc-WLEDs.

Laser-Induced Tunable White Light Emission in Yb3+/Er3+/Tm3+ Ion-Doped La2Ti2O7

A series of compounds with the general formula (La1−xREx)2Ti2O7 (x = 0.005, 0.015, and 0.025) doped with Yb3+, Er3+, and Tm3+ rare Earth ions were prepared by the traditional solid-state reaction at 1350 °C for 24 h. The X-ray powder diffraction technique, high-resolution transmission electron microscopy, and photoluminescence spectroscopy technique were used to characterize the structure and optical properties of the compounds. All compounds showed a single-phase orthorhombic structure with a space group Pna2 1, as confirmed by JCPDS (Cart No: 01-070-1690). The La1.9Yb0.04Er0.01Tm0.05 Ti2O7 nanocrystals exhibited intense tunable white light luminescence signals in the full spectrum, and green and blue emissions were predominant in the Yb3+/Er3+− and Yb3+/Tm3+-doped titanates, respectively. In this study, the influence of concentration and excitation power on the upconversion luminescence, color, and calculated laser-power-induced heating performance of La2Ti2O7 nanophosphors were investigated at room temperature.

Tunable White Light Emission of a Metal-Organic Framework Based on a Bisquinoxaline Derivative by Introducing Red-Green Cationic Dyes.

The unique structural advantages give metal-organic frameworks (MOFs) a special use as host substrates to encapsulate organic dyes, which would result in specific host-guest composites for white-light phosphors. In this work, an anionic MOF exhibiting blue emission was constructed using bisquinoxaline derivatives as photoactive centers, which could effectively encapsulate rhodamine B (Rh B) and acriflavine (AF) to form an In-MOF ⊃ Rh B/AF composite. By simply adjusting the amount of Rh B and AF, the emitting color of the resulting composite could be easily adjusted. The formed In-MOF ⊃ Rh B/AF composite exhibits broadband white light emission with ideal Commission International ed'Eclairage (CIE) coordinates of (0.34, 0.35), a color rendering index of 80.8, and a moderately correlated color temperature value of 5193.96 K. This strategy can be easily extended to other blue-emitting MOFs and dyes, thus opening up new prospects for the development of white-light-emitting materials.

Tunable white-light emission and afterglow of Eu3+ doped Gd2Zr2O7 phosphors

The undoped and Eu-doped Gd2Zr2O7 phosphors with different concentrations were prepared by the conventional solid-state reaction method. By varying the Eu3+ concentration, under the 256 nm excitation wavelength, the emission colour of the Gd2Zr2O7:Eu3+ phosphors can be tuned over a broad region. The synthesized phosphors were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. The PL spectra show the 5D0→ 7FJ (J = 1, 2 and 3) transition of Eu3+ and describe the afterglow properties of these phosphors which may be applicable for the development of white-LED (WLED).

Ligand induced phase-controlled synthesis of copper halide perovskite nanocrystals towards tunable white light emission

Recently, copper halides have attracted considerable interest for their excellent photoluminescence properties, low-cost and non-toxicity. Herein, we report the phase control in the synthesis of Cs3Cu2I5 and CsCu2I3 nanocrystals. The crystalline phase of the products can be tuned by changing the volume ratio of the ligand pair of oleic acid (OA) and oleylamine (OLA). Blue-emissive Cs3Cu2I5 and yellow-emissive CsCu2I3 nanocrystals can be obtained with the ratio of OA/OLA of 0.5:0.5 and 1:0.6, respectively. Interestingly, the composite of Cs3Cu2I5 and CsCu2I3 with ratio of OA/OLA of 1:0.8 exhibits tunable white light emission from cold white to pure white to neutral white.

Tunable Efficient White Emission in Holmium Doped Double Perovskites Cs2KInCl6 via Antimony Sensitization

AbstractRecently, ns2 metal ions (such as Bi3+ and Sb3+) doped double perovskites have captured intense attention for their efficient emission, however, achieving efficient and tunable white light emission is always an enormous challenge. Herein, Sb3+/Ho3+ co‐doped Cs2KInCl6 double perovskites are proposed, and the photoluminescence results show that there are two emission bands, one broad cyan emission band stems from self‐trapped exciton (STE) in [SbCl6]3‐ octahedron, while another red emission band derives from the f‐f transitions of Ho3+. The emission processes for Sb3+/Ho3+ co‐doped Cs2KInCl6 show that Sb3+ can act as the sensitizer to activate Ho3+ emission, which is due to the energy transfer channel from STE to Ho3+. As the Ho3+ concentration increases, the luminous color of Sb3+/Ho3+ co‐doped Cs2KInCl6 can be modulated from cyan to orange under 315 nm light irradiation, and the white emission can even be obtained with a photoluminescence quantum yield of 90 ± 2% when the energy‐transfer efficiency is 50%. Finally, single compound white‐light emitting diodes and fluorescent anti‐counterfeiting labels based on 0.5%Sb3+/60%Ho3+ co‐doped Cs2KInCl6 are fabricated. This work provides an effective strategy to achieve efficient tunable white emission in lead‐free double perovskites through ns2 metal and lanthanide ion co‐doping.

Warm to cool tunable ultra-stable white light emissions from carbon dots -Tb3+ - Eu3+ doped silica

Development of ultra-stable, solid-state, cost-effective phosphors for white light emitting devices with high color rendition is in high demand. In this work, we prepared carbon quantum dots (CQDs) by a hydrothermal method with an average size ranging from 2 to 8 nm which exhibits low toxicity. Optical analysis confirmed the influence of both Cu2+ and Fe3+ ions and the excitation-dependent fluorescence of CQDs are effectively quenched by addition of Fe3+ ions. The excitation dependent emission property of CQDs and degradation resistant blue emission of CQDs-silica are utilized to construct CQDs-Europium–Terbium doped silica matrices for stable multi-colour emissions upon different excitation wavelengths. Optimized composition of CQDs with Terbium and Europium ions produced white light emissions under UV exposure of 370–393 nm. Continuous tuning from warm white emission to cool white emission with moderate CRI is achieved by varying the concentration of CQDs. The ultra-stable white emissions which last long for a year, reveals the potential WLED applications of these solid-state luminescent materials.

White light emission from coumarin and rhodamine derivatives based on RGB multicomponent system

The mixture of red, green, and blue (RGB) organic fluorophores in a single blend is becoming more relevant to produce metal-free, low cost and color tunable white light emission. Herein we describe the combination of pure organic molecules based on the coumarin and rhodamine frameworks that generated broad or multi-band emission in both solution and solid forms. The derivatives of coumarin (CB), furocoumarin (CG) and rhodamine (CR1 and CR2) were synthesized and characterized using 1H NMR, 13C NMR, FTIR and ESI-MS spectroscopic techniques. The “closed-form” of the synthesized rhodamines have been further elucidated with the single crystal X-ray analysis. Their photophysical, thermal stability and electrochemical properties have been investigated, accompanied by DFT calculations to assess the plausible mechanism responsible for white light along with their eminent characteristics. Single mixture of ethanol-solubilized CR2:CG:CB in the ratio of 3:10:3 showed extremely pure white light fluorescence with CIE coordinates of (0.32, 0.33) when excited at 360 nm while CR1:CG:CB revealed almost pure white light (0.27, 0.32) in the ratio of 1:2:1 when excited at a much longer wavelength (λex = 395 nm). The results obtained are very encouraging in such a way that only minimal proportions of the blue and green fluorophores are required in the single mixture for a highly efficient FRET system when combined with the newly synthesized rhodamine derivatives. The ratio differences can be down to 30–42 % as compared to white light mixture with the commercial red R640. Furthermore, all of the synthesized RGB components exhibit reasonably good thermal stability with onset of decomposition above 210 °C, endowing their suitability for general applications of optoelectronic devices. The HOMO-LUMO energy band gaps from the cyclic voltammetry and geometrical optimized structures of the ground state are generally in nice agreement. White light emission was also generated when the polymer mixtures containing each RGB emitters was coated on a commercial UV-LED, demonstrating potential low cost and purely organic device set-up.

A temperature-responsive artificial light-harvesting system in water with tunable white-light emission

A tadpole-type amphiphilic monomer containing cyanostilbene and oligo(ethylene glycol) chains has been designed and synthesized, which can be used to construct a thermo-responsive light-harvesting system in water with tunable white-light emission.

Efficient manipulation of Förster resonance energy transfer through host-guest interaction enables tunable white-light emission and devices in heterotopic bisnanohoops.

In this study, we synthesized and reported the heterotopic bisnanohoops P5-[8,10]CPPs containing cycloparaphenylenes (CPPs) and a pillar[5]arene unit, which act not only as energy donors but also as a host for binding energy acceptors. We demonstrated that a series of elegant FRET systems could be constructed successfully through self-assembly between donors P5-[8,10]CPPs and acceptors with different emissions via host-guest interaction. These FRET systems further allow us to finely adjust the donors P5-[8,10]CPPs and acceptors (BODIPY-Br and Rh-Br) for achieving multiple color-tunable emissions, particularly white-light emission. More importantly, these host-guest complexes were successfully utilized in the fabrication of white-light fluorescent films and further integrated with a 365 nm LED lamp to create white LED devices. The findings highlight a new application of carbon nanorings in white-light emission materials, beyond the common recognition of π-conjugated molecules.

Tunable Bright White Light Emission with Ultra‐High Color Rendering Index Induced by Trigonal Bipyramid Unit

AbstractEfficient broadband emitting organic–inorganic metal hybrids (OIMHs) have attracted great attention recently as promising single‐component white light emitters. Here a new zero‐dimensional (0D) OIMH (C13H14N)2InCl5 (C13H14N+ = N‐methyldiphenylammonium) is reported, which features unique five‐coordinated [InCl5]2− trigonal bipyramid motif. For the first time, it is demonstrated that the trigonal bipyramid units in 0D OIMH can act as luminescence centers, showing blue emission under UV light. Remarkably, incorporating Sb3+ in [InCl5]2− trigonal bipyramids induces a new dual‐band emission at 540 and 735 nm resulting from the singlet and triplet self‐trapped excitons in [SbCl5]2−, leading to complete coverage of the entire visible spectrum. The resulting emissions in (C13H14N)2InCl5:Sb3+ are tunable from cold to warm white with the correlated color temperatures changing from 5574 to 3473 K and more importantly, an ultra‐high color rendering index (CRI) up to 96 being observed, which is comparable to the highest value in hybrid metal halides. A high photoluminescence quantum yield of 46.26% is simultaneously obtained in this system. This work demonstrates that the 0D OIMH with trigonal bipyramid motif is an excellent system for realizing the single‐component white light emission with both high efficiency and ultra‐high CRI.

Excitation-Dependent Tunable White Light of ns2 Ions Doped Rb2SnCl6 Vacancy Ordered Double Perovskite.

Single-matrix white light-emitting diodes are still a challenge. Achieving tunable white light emission from lead-free perovskites attracts much attention. Herein, nanoscale Rb2SnCl6 (RSC) vacancy ordered double perovskite were synthesized by an optimized precipitation method. Further, using ns2 ions (Bi3+, Te4+, and Sb3+) doped RSC vacancy ordered double perovskite to obtain broadband blue, yellow-green, and orange-red emission. The color temperature adjustable high-quality white light emission based on the codoping strategy is obtained by controlling the doping ratio of Bi3+ and Te4+. Additionally, the white light-emitting diodes encapsulated by this single matrix white luminescent material exhibit excellent stability. Combined with theoretical calculations, it is elucidated that these high-efficiency emissions are not only derived from the unique electronic transition of ns2 ions but also related to the energy band properties and the crystal field. This work shows that ns2 ions doped RSC vacancy ordered double perovskite can meet the needs of different luminous colors and color temperature tunable white light emission. Meanwhile, it is a strong competitor to replace the lead-based perovskite.

Short Aromatic Diammonium Ions Modulate Distortions in 2D Lead Bromide Perovskites for Tunable White-Light Emission

White-light broadband emission in the visible range from the low-dimensional halide perovskites is commonly attributed to structural distortions in lead bromide octahedra. In this paper, we report Dion–Jacobson-phase two-dimensional (2D) lead bromide perovskites based on short aromatic diammonium cations, p-phenylene diammonium (pPDA), m-phenylene diammonium (mPDA), and two 1D compounds templated by o-phenylene diammonium (oPDA). All of the compounds exhibit white-light emission. Single-crystal X-ray diffraction analysis reveals that the distortion of the Pb octahedra is influenced by the stereochemistry of the cations and their interactions with the perovskite layers. Solid-state 1H and 207Pb NMR spectroscopy analysis further confirms this trend, whereby different 1H and 207Pb chemical shifts are observed for the pPDA and mPDA spacer cations, indicating different hydrogen-bonding interactions and octahedral distortions. Owing to the octahedral distortion, 2D (mPDA)PbBr4 compounds exhibit broader white-light emission than 2D (pPDA)PbBr4. Density functional theory calculations suggest that (pPDA)PbBr4 and (mPDA)PbBr4 are direct-band-gap semiconductors, and they exhibit larger electronic band gaps and effective masses than the Ruddlesden–Popper-phase (BA)2PbBr4. Among the films of these compounds, 2D (mPDA)PbBr4 shows the best stability, which is attributed to stronger hydrogen-bonding interactions in the material.