White Light Emission Research Articles

Electron beam-induced white emission from iridium complexes-doped polymer dots

Radiation detection plays an important role in diverse applications, including medical imaging, security, and display technologies. Scintillators, materials that emit light upon exposure to radiation, have garnered significant attention due to their exceptional sensitivity. Previous research explored polymer dots (P-dots) doped with iridium complexes as nano-sized scintillators for radiation detection, but these were constrained to emitting specific colors like red, green, and blue, limiting their utility. Recently, there has been a breakthrough in the development of white light emitters stimulated by UV–visible light. These emitters exhibit a broad spectral range in the visible wavelength, enhancing contrast and simplifying detection by visible-light sensors. Consequently, the quest for white color scintillators in radiation detection has emerged as a promising avenue for enhancing scintillation efficiency. In this study, we present a novel approach by applying P-dots doped with two iridium complexes to create white light-emitting nano-sized scintillators. These scintillators offer a wider spectral coverage within the visible-light wavelength range. Under UV light (365 nm) excitation, our synthesized P-dots exhibited remarkable white light emission. Moreover, when excited by electron beam irradiation, we observed the clear emission close to white emission which is valuable for improving the detection of radiation.

Pd-Catalysed Direct Arylation of Distyrylbenzene: Strong Dual-state Fluorescence and Electrochromism.

Distyrylbenzenes (DSBs) are well-known for their strong multicolour fluorescence. Fluorescence tuning of DSB via further functionalization/arylation, on the other hand, is uncommon. This paper reports a Pd-catalysed direct arylation approach for introducing different aryl groups onto fluorobenzene-containing DSB moiety (7) in high yields (67-72 %). The versatile methodology allows the substitution of neutral [tolyl (1)], electron-deficient [p-formyl benzene (2), p-acetyl benzene (3), p-nitrobenzene (4)] and electron-rich [carbazole (5), triphenylamine (6)] aryl groups. The electron-deficient aryls render mono-substitution, while the electron-rich counterparts promote di-substitution. The compounds (1-6) show blue, green, and yellow fluorescence in both the solution and solid states; the fluorescence quantum yields reach >98 % and the peak maxima span from 425 to 560 nm. The mono-carbazole DSB (5) exhibit white light emission (WLM) in polar solvents (acetone, DMF, CH3CN, DMSO and NMP) with very high fluorescence quantum yields (φf) of 60-80 %. For WLM, such high efficiency (φf) is somewhat uncommon. Moreover, visible-to-NIR reversible electrochromism is demonstrated by the TPA-integrated DSB (6). The colour of 6 changes from pristine light yellow to orange, and the absorption maxima shifts from 372 to 1500 nm when a positive potential of 1.0 V vs Ag/Ag+ is applied. Moreover, the system shows high colouration efficiency in the NIR region with fast switching speeds for colouration and decolouration as fast as 0.98 s and 1.05 s.

Unveiling the luminescence property of Pr-incorporated barium cerate perovskites for white LED applications

Abstract The various structural and conductive attributes of barium cerate, BaCeO3 position it as a highly promising matrix for energy storage purposes. The current study illustrates that barium cerate can be effectively tailored by introducing trivalent praseodymium ions, thereby enhancing its optical properties as well. In this work, single-phased orthorhombic crystalline powders of barium cerate incorporated with Pr3+ (BaCeO3: Pr3+) were synthesized using the gel combustion procedure, followed by calcination. We conducted a comprehensive investigation into their crystal structure, vibrational characteristics, optical properties, and potential applications in wLEDs. The structure refinement indicates that Pr3+ occupies Ce4+ site, which results in the expansion of the cell and facilitates the generation of defects such as Pr Ce ′ ${\mathrm{Pr}}_{\text{Ce}}^{\prime }$ and oxygen vacancies V O ⋅ ⋅ ${V}_{\text{O}}^{\cdot \cdot }$ . By correlating information gathered from diffuse reflectance spectra with that obtained from photoluminescence spectra, we gained a deeper understanding of the electronic level structure and the mechanism of energy transfer. We successfully achieved a finely tuned cool white light emission with very low color purity (CP), a high color rendering index (CRI), and a high correlated color temperature (CCT) with a quantum efficiency of 36.3 % by exciting the material with a 321 nm wavelength. Because of the transfer of energy within activators through dipole–dipole interaction, luminescence quenching occurs when Pr3+ concentration reaches 1 wt%. To the best of our knowledge, this is the initial investigation of luminescence properties of Pr-incorporated barium cerate perovskites.

Luminescence of silver, thulium and ytterbium doped oxyfluoride glasses

Abstract Silver and lanthanide (Tm3+, Yb3+) doped oxyfluoride glasses have been prepared by melt-quenching method. The absorption of the glasses was measured in the range from 350 to 550 nm revealing the absorption edges of Ag nanoclusters and Tm3+ transition. The photoluminescence spectra of the glasses were detected in the range from 400 to 1100 nm under excitation in the range from 300 to 500 nm. The photoluminescence excitation spectra showed that Ag nanoclusters and Tm3+ ions can effectively harvest energy in UV-range and convert to visible and infrared (through emission by Yb3+ ions) ranges making the glasses perspective as white light emitters and solar spectrum downconverters.

A Statistical Study of Solar White-Light Flares Observed by the White-Light Solar Telescope of the Lyman-Alpha Solar Telescope on the Advanced Space-Based Solar Observatory (ASO-S/LST/WST) at 360 nm

Solar white-light flares (WLFs) are those accompanied by brightenings in the optical continuum or integrated light. The White-light Solar Telescope (WST), as an instrument of the Lyman-alpha Solar Telescope (LST) on the Advanced Space-based Solar Observatory (ASO-S), provides continuous solar full-disk images at 360 nm, which can be used to study WLFs. We analyze 205 major flares above M1.0 from October 2022 to May 2023 and identify 49 WLFs at 360 nm from WST observations, i.e. with an occurrence rate of 23.9%. The percentages of WLFs for M1 – M4 (31 out of 180), M5 – M9 (11 out of 18), and above X1 (7 for all) flares are 17.2%, 61.1%, and 100%, respectively, namely the larger the flares, the more likely they are WLFs at 360 nm. We further analyze 39 WLFs among the identified WLFs and investigate their properties such as white-light enhancement, duration, and brightening area. It is found that the relative enhancement of the white-light emission at 360 nm is mostly (>90%) less than 30% and the mean enhancement is 19.4%. The WLFs’ duration at 360 nm is mostly (>80%) less than 20 minutes and its mean is 10.3 minutes. The brightening area at 360 nm is mostly (>75%) less than 500 arcsecond2 and the median value is 225. We find that there exist good correlations between the white-light enhancement/duration/area and the peak soft X-ray (SXR) flux of the flare, with correlation coefficients of 0.68, 0.58, and 0.80, respectively. In addition, the white-light emission in most WLFs peaks around the same time as the temporal derivative of SXR flux as well as the hard X-ray emission at 20 – 50 keV, indicative of the Neupert effect. It is also found that the limb WLFs are more likely to have a greater enhancement, which is consistent with numerical simulations.

Luminescent CdS quantum dot-embedded glass for W-LED lighting and X-ray imaging

Quasi-zero-dimensional quantum dots (QDs) have garnered significant attention owing to their distinct structural attributes, quantum confinement behaviors, optoelectronic characteristics, etc. Regrettably, their susceptibility to stability poses a challenge. In this context, leveraging rational component regulation and crystallization process optimization strategies, we presented the successful preparation of CdS QDs silicate glass through the amalgamation of melt-quenching and controlled crystallization. The optical and morphological analysis substantiated the accomplishment of in-situ precipitation of CdS QDs within the glass matrix, with grain sizes <20 nm. Integrating CdS QDs into an inorganic glass matrix remarkably augmented its fluorescence thermal stability, enabling the preservation of 85.1 % of the room-temperature luminescent intensity even at an elevated temperature of 150 °C. Moreover, the encapsulated W-LED device by near-UV LED chip, CdS QDs glass, and BaMgAl10O17:Eu2+ phosphor exhibited a warm white-light emission characterized by suitable chromaticity coordinates (0.3741, 0.3452) and a notably high color rendering index (CRI = 93). Ultimately, the radioluminescence behavior of CdS QDs glass was unveiled by utilizing it as the scintillator wafer in an X-ray imaging system, which clearly demonstrated the structure of spring encapsulated within an opaque capsule. In a nutshell, these demonstrations unequivocally emphasize the substantial potential merits of CdS QDs glass, particularly in the domains of long-term W-LED lighting and X-ray imaging applications.

Two helical Schiff bases with “AIE+ESIPT” characteristics exhibiting selective ion recognition properties

Two racemic Schiff bases (H4L1 and H4L2) were synthesized and characterized, and the crystal structures indicated their helical configurations with equal amounts of P- and M-helicity. The aggregation-induced emission (AIE) and selective ion recognition properties of H4L1 and H4L2 were investigated using UV–vis absorption and fluorescence spectra. The results showed that both H4L1 and H4L2 exhibited obvious “AIE + ESIPT” characteristics in THF/H2O solution upon increasing the water fraction. Both H4L1 and H4L2 displayed an obvious turn-off fluorescence response to Cu2+ and F−, and a slight turn-off response to Fe3+ in DMSO, while they displayed an efficient selective ion recognition of Cu2+ in THF/H2O (1: 1, V/V). The corresponding stoichiometry ratio, association constant, Stern-Volmer quenching constant, and the detection limits were determined via Job's plots, UV–vis spectra titration as well as fluorescence spectra titration experiments. The crystal structures of the complexes obtained from the interactions of H4L1 with Cu2+ and Fe3+ illustrated their binding modes and binding differences, which helped us interpret the ion recognition mechanism of H4L1 and H4L2. In addition, the application of H4L2 on test strips was performed, indicating that H4L2 can be used for the rapid detection of Cu2+ and F− in THF. The acid-responsive fluorescence behavior of H4L2 showed that the white light emission can be obtained upon the addition of hydrochloric acid or aldehyde c into H4L2.

Efficient White Light‐Emitting Diodes Based on Cu(I) Activated Single‐Phase Halide Single Crystals

Single‐phase white light emitters have become a potential substitute for tricolor phosphor mixtures for the white light‐emitting diodes (WLEDs) application to simplify device structure and eliminate self‐absorption. Newly developed low‐dimensional halides, noted for their highly efficient luminescent characteristics, have seen increasing interest in recent years. Herein, highly efficient white‐light emission is demonstrated in single‐phase zero‐dimensional halide single crystal, namely monovalent Cu‐doped Cs2HfCl6. Cs2HfCl6:Cu single crystals have three luminescent centers. Two emission peaks at 365 nm and 380 nm correspond to the intrinsic self‐trapped excitons emission and a defect‐related trapped exciton emission, respectively. Cu doping introduces an intense Cu‐bound exciton emission peaking at 540 nm with a large Stokes shift of 250 nm and a high photoluminescence quantum yield of 68%. With different excitation wavelengths and Cu‐doping concentrations, Cs2HfCl6:Cu single crystals show tunable emissions. Under 254 nm ultraviolet light excitation, Cs2HfCl6:0.5%Cu yields cold white light with a high color rendering index (Ra = 87.3). These findings demonstrate the potential of Cs2HfCl6:Cu as a promising phosphor for cold WLEDs.

Synthesis of Metastable Silver-Lanthanide Double Perovskite Nanocrystals with White-Light Emission.

Four silver-lanthanide double perovskite nanocrystals, namely, Cs2AgSmCl6, Cs2AgEuCl6, Cs2AgGdCl6, and Cs2AgErCl6, were synthesized for the first time. These four double perovskites have yet to be reported in any form and are found to be metastable in the bulk phase. By using the colloidal hot-injection synthesis method, the metastable double perovskite phase can be arrested kinetically. These lead-free nanocrystals show a broadband emission owing to the self-trapped exciton recombination, with Cs2AgEuCl6 exhibiting the characteristic f-f emission from Eu3+.

Enhancing luminescence, tuning emission colors, and improving temperature sensitivity in NaGd(MoO4)2 multilayer thin films

A thin film with a sandwich structure of NaGd(MoO4)2: Yb3+@Yb3+/Ho3+@Yb3+ was successfully prepared using the spin-coating method. A comparative analysis of this sandwich-structured film with other films having the same doping composition and spin coating times showed that the emission intensity of the former was enhanced. We attribute the luminescence enhancement of the sandwich-structured film to the presence of Yb3+ ions in both the top and bottom layers. This overcomes the concentration quenching effect imposed by the Yb3+/Ho3+ system's concentration limit. Moreover, the warm white light emission of the NaGd(MoO4)2:Yb3+@Yb3+/Tm3+@Yb3+/Ho3+@Yb3+ film was successfully achieved by introducing Yb3+/Tm3+ layers, and tuning from blue to white to yellow was realized by adjusting the number of spin coatings and the proportion of Yb3+/Tm3+ and Yb3+/Ho3+ layers. Finally, we found that sandwich-structured films have better temperature sensitivity compared to powder materials and other structured films. These results indicate that rare-earth doped NaGd(MoO4)2 thin films have great potential in the fields of luminescence, color display, and temperature sensing. The adjustment of luminescence color can be achieved by manipulating the micro/nano film structure, and the spin-coating process can effectively improve the temperature sensing characteristics.

Cool white light generation of Dy3+ activated aluminum sodium calcium borate glass for W-LED application

The Dy3+-activated aluminum sodium calcium borate glass with white light emission might have been created through the melt-quenching process. This research explores the optical and luminescence characteristics of borate glasses. Dy3+-activated glasses exhibit absorption in the visible (VIS) and near-infrared spectrums. The absorption starts from the 6H15/2 ground state to the higher state concerning optical characteristics. The emission spectra of dysprosium-doped glasses' photoluminescence show greater intensity at 483 nm (blue light) and 575 nm (yellow light), which are critical wavelengths for white light-generating materials. The luminescence intensity of Dy3+ ions increased up to a 0.50 mol% concentration, while the decay time decreased with an increasing dysprosium ion concentration. The emission spectra were used to estimate the CIE 1931 chromaticity and corresponding color temperature, revealing a shift towards the cold white light location at that temperature. The stimulated emission cross-section is calculated via the Judd-Ofelt theory. All characteristic outcomes suggest that the existing dysprosium-enabled glasses are excellent materials for generating cool white light in W-LED applications.

Multiemission of Ce3+ from a Single Crystallographic Site Induced by Disordering of Ions.

White-light emission with a single activator is an attractive function of phosphors. In this work, we investigated the photoluminescence properties of Ca5.7Y1.3Si7O16.7N3.3, which is a compound denoted as Ca4+xY3-xSi7O15+xN5-x discovered by our group, with Ce-activation using optical measurements and density functional theory (DFT) calculation. Samples showed a tunable emission from purple to white under ultraviolet (UV) light. In this compound, Ca and Y as well as anions are distributed disorderly, and Ca/Y ions occupy two crystallographically distinct sites; those sites are possible sites for Ce substitution. DFT calculation and structural refinement revealed that the tunable emission was generated by Ce at the crystallographically equivalent site but with distinct local structures caused by the disordering of cations and anions. As far as we know, this is the first report about a white-light-emitting phosphor with only Ce activation.

Photochromism and single-component white light emission from a metalloviologen complex based on 1,5-naphthyridine.

Metalloviologens, as emerging electron-transfer photochromic compounds, have shown intriguing properties such as radiochromism, photochromism and photoconductance. However, only a limited number of them have been reported so far. Exploration of new metalloviologens is strongly desired. Herein, we report a new solvothermally synthesized metalloviologen complex [CdCl2(ND)2]n (1, ND = 1,5-naphthalenes) that exhibits photochromic and intrinsic white light emission properties. Density functional theory calculation results reveal that the photochromism could be assigned to photoinduced electron transfer from chlorine atoms to ND molecules. The photoinduced charge-separated states are heat/air stable, attributed to the delocalization of ND and strong intermolecular π-π interactions. Besides, complex 1 consistently emits intrinsic white light when excited with 340-370 nm UV light, achieving high color rendering index (CRI) values (82.54-94.04). By adjusting the excitation wavelength, both "warm" and "cold" white light emission can be produced, making it suitable for the application of a white light emitting diode (WLED). Thus, this work demonstrates that the ND-based metalloviologen is not only helpful in producing photochromism, but also beneficial for creating white-light emission.

Bright white light emission from lanthanide oxide LaGdO3 for LED lighting by Bi3+ to Eu3+ energy transfer.

Phosphors with intrinsic white light emission are of great potential in constructing high-quality white LEDs (WLEDs). In this work, we propose the use of energy transfer from Bi3+ to Eu3+ ions for white light emission. A unique Bi3+-activated phosphor LaGdO3 (LGO):Bi3+ was generated using the conventional high-temperature solid-state process. An energy transfer was established by introducing Eu3+ into the phosphor composition. The emission colour of LGO:Bi3+,Eu3+ phosphors changes from cyan to white to orange-red depending on the Bi3+/Eu3+ doping proportion. The energy transfer between the Bi3+ and Eu3+ ions results from the dipole-dipole interaction. The LGO:Bi3+,Eu3+ phosphors were combined with a near-ultraviolet chip to successfully create a single-component WLED device with a colour-rendering index of 92.4. Our work demonstrates the energy transfer as a route for single-component white light emission and makes LGO:Bi3+,Eu3+ phosphors one of the candidate materials for near-ultraviolet lighting.

Defect Induced high-color-rendering white light emissions from Ag-doped ZnO

It is crucial to find high-quality white-light phosphors that are simple to synthesize in order to create efficient lighting. In this pursuit, the focus has been on achieving the emission of white light in ZnO and Ag-doped ZnO emerging as a promising phosphor candidate. The optimized ZnO nano phosphors demonstrated visible-light emission with ideal Commission international de I E “Eclairage frequently abbreviated as coordinates (x = 0.33, y = 0.33 ) and a correlated color temperature of 6200 K, and a color rendering index of 100 for equivalent to day white light. Furthermore, under certain ideal processing conditions, neutral white-light emission (x = 0.33, y = 0.33 at λex = 280 and 370 nm) with a Color correlated temperature (CCT) of 5500 K(approx.) was achieved. The Color Rendering Index (CRI) of the ZnO and Ag:ZnO nanoparticles exceeded 90, with high values approaching 96%, which is necessary for accurately portraying object colors in comparison to natural sunshine. The research findings revealed a decrease in the FS emission intensity with all the UV excitation when Ag doped in ZnO, which aligns well with the principles of Stern-Volmer quenching. A reduction in intensity was observed which may be due to the Ag dopant interacting with the luminescent nanoparticles and causing a reduction in their emitted light. The study successfully develops and optimizes ZnO-based nano phosphors with tailored white-light emission characteristics, presenting a promising solution for achieving energy-efficient and high-quality white-light sources for various lighting applications.

Red-emitting ionic fluorophores: anion-dependent tunable fluorescence, chlorinated solvent sensing, white light emission and latent fingerprinting

TPA-P ionic fluorophores exhibited anion-dependent tunable fluorescence, chlorinated solvent sensing with isomer distinguishing ability, white light emission with blue-emitting PSS and excellent LFPs imaging on various substrates.

Pressure enables high-standard white light emission and significant emission enhancement in a 2D halide perovskite

A 2D OIHP, (CHA)2PbBr4, exhibits significant pressure-induced emission enhancement at 2.0 GPa. The luminescence color of the crystal changes from yellow to white under pressure.

Phosphor-free micro-pyramid InGaN-based white light-emitting diode with a high color rendering index on a β-Ga2O3 substrate.

We demonstrate the InGaN/GaN-based monolithic micro-pyramid white (MPW) vertical LED (VLED) grown on (-201)-oriented β-Ga2O3 substrate by selective area growth. The transmission electron microscopy (TEM) reveals an almost defect-free GaN pyramid structure on (10-11) sidewalls, including stacked dual-wavelength multi-quantum wells (MQWs). From the electroluminescence (EL) spectra of the fabricated MPW VLED, a white light emission with a high color rendering index (CRI) of 97.4 is achieved. Furthermore, the simulation shows that the light extraction efficiency (LEE) of the MPW VLED is at least 4 times higher compared with the conventional planar LED. These results show that the MPW VLED grown on β-Ga2O3 has great potential for highly efficient phosphor-free white light emission.

White Light Emission and Superior Color Stability in a Single-Component Host with Exceptional Eminent Color Rendering and Theoretical Calculations on Duv for Color Quality

Correlated color temperature (CCT) is widely used to describe the chromaticity of white light sources, although chromaticity is only two-dimensional, and the distance from the Planckian locus is typically absent....

Adjustable ultraviolet and white light dual emission phosphor Y2Sr(Ga1-yAly)4SiO12:xPr3+ for health lighting.

Mid-ultraviolet light (290-320 nm) can promote human vitamin D synthesis, which helps in the prevention and treatment of rickets and cartilage disease. For people who lack sufficient ultraviolet radiation all year round, it is significant to supplement the ultraviolet component in daily lighting sources. However, there are few luminous materials showing a combination of mid-ultraviolet light and white light emission on the market. Here, we designed a new material, Y2Sr(Ga1-yAly)4SiO12:xPr3+ (YSGAS:xPr3+), which achieves dual emission of 320 nm ultraviolet and white light from a single substrate with a single doped phosphor. Without Al3+ ions, the emission intensity of the Y2SrGa4SiO12:xPr3+ phosphor shows a contribution-dependent relationship, and concentration quenching due to exchange interaction. The crystal field environment was regulated by partially replacing Ga3+ ions with Al3+ ions. After introducing Al3+, YSGAS:xPr3+ phosphors exhibit dual ultraviolet emission (320 nm) and visible light emission. The emission color of YSGAS:xPr3+ can be adjusted by changing the Al3+ concentration, and Y2Sr(Ga0.6Al0.4)4SiO12:1%Pr3+ emits both ultraviolet light and white light. The LED device prepared by using the YSGAS:Pr3+ phosphor and chips shows a color temperature of 4858 K and appropriate CIE coordinates of (0.3474, 0.3390), indicating wide application prospects in the field of "health lighting" for particular populations.