Application In Light-emitting Diodes Research Articles

Enhancement of spontaneous emission from CdSe/ZnS quantum dots through silicon nitride photonic crystal cavity based on miniaturized bound states in the continuum.

Colloidal CdSe/ZnS quantum dots (QDs) exhibit excellent optical properties for wide potential applications in light-emitting diodes, solar concentrators, and single-photon sources. However, the ultra-thin films with low concentration of QDs still encounter inefficient photoluminescence (PL) and poor directionality of radiation, which need to be enhanced using nanophotonics device designs. Here we design and experimentally demonstrate an on-substrate silicon nitride (SiN) photonic crystal (PhC) microcavity encapsulated by a layer of PMMA hosting CdSe/ZnS QDs. The miniaturized bound states in the continuum (BIC) supported by our structures, provide high-Q resonant modes with highly-directional emission patterns. Experimental results show that the BIC mode in the microcavity has a Q-factor up to 7000 owing to the symmetric refractive index distribution along the Z-direction, rendering 8.5-fold enhancement of PL intensity and 8.4-fold acceleration of radiative emission rate. Our work provides a practical way for constructing efficient on-chip surface-emitting light sources on silicon-based integrated photonic devices.

Research progress on surface modifications for phosphors used in light-emitting diodes (LEDs).

Stable and efficient phosphors are highly important for light-emitting diodes (LEDs) with respect to their application in solid-state lighting, instead of conventional lamps for general lighting. However, some problems, like low stability, low photoluminescence (PL) efficiency, and serious thermal degradation, are commonly encountered in phosphors, limiting their applications in LEDs. Surface modifications for some phosphors commonly used in LED lighting, including fluoride, sulphide, silicate, oxide, nitride, and oxynitride phosphors, are presented in this review. By forming a protective surface layer, the stabilities against moisture and high temperature of fluoride- and sulphide-based phosphors were strengthened; by coating inorganic and organic materials around the particle surface, the PL efficiencies of silicate- and oxide-based phosphors were improved; by passivation treatment upon the phosphor surface, the thermal degradation of nitride- and oxynitride-based phosphors was reduced. Various technologies for surface modification are described in detail; moreover, the mechanisms of stability strengthening, PL efficiency improvement, and thermal degradation reduction are explained. In addition, embedding of phosphors in inorganic glass matrix, especially for quantum dots, is also introduced as an effective method to improve phosphor stability for LED applications. Finally, future developments of surface modification of phosphors are proposed.

Red, yellow, green, and blue light-emitting highly crystallized graphene quantum dots derived from lignin: controllable syntheses and light-emitting diode applications

“Lighting up” lignin: synthesis of multicolour-emitting GQDs with high crystallinity from lignin within 12 h and their successful application to multicolour LEDs.

Opportunity of lead-free metal halide perovskites for electroluminescence

<p>Lead halide perovskites (LHPs), which have demonstrated exceptional optical and electrical properties are promising candidates for electroluminescent light-emitting diodes (LEDs). However, concerns about the toxicity and stability have hindered their commercialization. In recent years, lead-free metal halide perovskites (LFMHPs) have emerged as promising alternatives, and significant progress has already been made in developing LFMHP-based LEDs. Nevertheless, their device performance is still inferior to that of well-developed LHP-based counterparts. To fully exploit LED applications and boost device performance, in this review, we provide a comprehensive overview of the currently explored different metal-based LFMHPs. We mainly focus on the preparation methods, crystal structure, optical properties, and LED applications of these materials. Furthermore, we conclude with a discussion regarding the key challenges and potential prospects in this field. We hope that this review will inspire more extensive research on LFMHPs from a new perspective and promote practical applications of LFMHP-based LEDs in multiple directions of current and future research.</p>

Repeated irradiation by light-emitting diodes may impede the spontaneous progression of experimental periodontitis: a preclinical study.

We investigated whether repeated irradiation with light-emitting diodes (LEDs) at a combination of 470 nm and 525 nm could suppress the progression of experimental periodontitis. A experimental periodontitis model was established in the second, third, and fourth premolars of the mandible in beagle dogs for 2 months. The spontaneous progression of periodontitis was monitored under the specified treatment regimen for 3 months. During this period, the animals were subjected to treatments of either plaque control only (control) or plaque control with LED application (test) at 2-week intervals. The clinical parameters included the probing pocket depth (PPD), gingival recession (GR), and the clinical attachment level (CAL). Histomorphometric analysis was performed using measurements of the length of the junctional epithelium, connective tissue (CT) zone, and total soft tissue (ST). There were significant differences in PPD between the control and test groups at baseline and 12 weeks. When the change in PPD was stratified based on time intervals, it was shown that greater differences occurred in the test group, with statistical significance for baseline to 12 weeks, 6 to 12 weeks, and baseline to 6 weeks. There was no significant difference in GR between the control and test groups at any time points. Likewise, no statistically significant differences were found in GR at any time intervals. CAL showed a statistically significant difference between the control and test groups at baseline only, although significant differences in CAL were observed between baseline and 12 weeks and between 6 and 12 weeks. The proportion of CT to ST was smaller for both buccal and lingual areas in the control group than in the test group. Repeated LED irradiation with a combination of 470-nm and 525-nm wavelengths may help suppress the progression of periodontal disease.

Dynamic changes of blue/red light supply affect yield, biometrical and biochemical characteristics of tomato cultivars

The utilization of Light Emitting Diodes (LED) is considered one of the most impacting innovations in modern tomato production systems. The characteristics of artificial light supplied to tomato in greenhouse conditions influence the fruit yield response over the year-round crop cycle. The present work aimed to evaluate the effects of dynamic artificial light application on the growth of two tomato hybrids. The experimental protocol was based on the factorial combination between two artificial light spectra supplied to plants (a spectrum composed of blue 450 nm, red 660 nm with deep pink 400-800 nm as a background, and a white 4000 K light as a control) and two early ripening tomato hybrids (‘Signum F1’ and ‘Meteor F1’). The use of blue/red light-emitting diodes (LEDs) in a growth chamber, accompanied by a gradual increase in the red component during the vegetation phase, significantly enhanced the yield of the two tomato cultivars, with an increase of 1.61 to 1.75 times compared to control plants exposed to white light. Notably, the predominant application of blue LEDs during the early stages of plant development resulted in a reduction in plant height by 1.2-1.5 times. The selected technology involving dynamic adjustments in blue/red light proportions led to a notable increase in chlorophyll and carotene levels in tomato leaves, with enhancements of 1.41-1.46 times and 1.29-1.37 times, respectively. Moreover, the variations in blue/red light demonstrated a significant positive impact on carotenoid accumulation in the fruit, resulting in an increase of 1.29 -1.37 times compared to control plants. The increase in fruit monosaccharide organic acid content in response to blue/red light application resulted in the production of tomato fruit with high taste index and nutritional value, suggesting interesting prospects of this new technology utilization

Exclusive confinement of Bi3+-activators in the triangular prism enabling efficient and thermally stable green emission in the tridymite-type phosphor CaBaGa4O8:Bi3.

Recently, Bi3+-activated phosphors have been extensively studied for potential applications in phosphor-converted white light-emitting diodes (pc-WLEDs). However, Bi3+ activators usually exhibit low quantum efficiency and poor thermal stability due to the outermost 6s6p-orbitals of Bi3+ being strongly coupled with the host lattice, inhibiting potential applications. Herein, we rationally design a novel phosphor CaBaGa4O8:Bi3+, which adopts a tridymite-type structure and crystallizes in the space group of Imm2. CaBaGa4O8:Bi3+ presents a bright green light emission peaking at 530 nm with a FWHM narrower than 90 nm. Comprehensive structural and spectroscopic analyses unravelled that Bi3+ emitters were site-selectively incorporated into the triangular prism (Ca2+-site) in CaBaGa4O8:Bi3+ since there exist two distinct crystallographic sites that can accommodate the Bi3+ ions. An excellent luminescence thermal stability of 73% of the ambient temperature photoluminescence intensity can be maintained at 423 K for CaBaGa4O8:0.007Bi3+. Impressively, the quantum efficiency (QE) of CaBaGa4O8:0.007Bi3+ was remarkably improved to 47.2% for CaBaGa4O8:0.007Bi3+,0.03Zn2+via incorporating the Zn2+ compensators without sacrificing the luminescence thermal stability. The high thermal stability and QE of CaBaGa4O8:0.007Bi3+,0.03Zn2+ are superior to most of the Bi3+-activated green-emitting oxide phosphors. The perspective applications in pc-WLEDs for CaBaGa4O8:0.007Bi3+,0.03Zn2+ were also studied by fabricating LED devices.

Bridging the gap from single molecule properties to organic semiconductor materials

This perspective discusses how single-molecule characterization techniques can help to establish structure–property relationships and further open up new paths for the rational design of organic semiconductor materials.

Spin–orbit charge transfer intersystem crossing and thermal activation delayed fluorescence (TADF) studies of compact orthogonal anthraquinone phenothiazine derivatives

Thermally activated delayed fluorescence (TADF) in compact electron donor–acceptor dyads has attracted great attention due to their potential application in organic light-emitting diodes.

Controllable construction of red thermally activated delayed fluorescence molecules based on a spiro-acridine donor.

Red and near-infrared (NIR) thermally activated delayed fluorescence (TADF) molecules show excellent potential applications in organic light-emitting diodes (OLEDs). Due to the lack of systematic studies on the relationship between molecular structures and luminescence properties, both the species and amounts of red and NIR TADF molecules are far from meeting the requirements for practical applications. Herein, four new efficient molecules (DQCN-2spAs, TPCN-2spAs, DPCN-2spAs and BPCN-2spAs) are proposed and their photophysical properties are theoretically predicted based on first-principles calculations and thermal vibration correlation function (TVCF) theory. The results show that all molecules exhibit red or NIR emissions and they have fast radiative decay rates and reverse intersystem crossing (RISC) rates, and the excellent TADF luminescence properties are predicted. Moreover, based on spiro-acridine (spAs) as the donor unit, the combination with different acceptors can change the dihedral angle between the ground state and the excited state, the bending degree of the donor is positively correlated with the reorganization energy, and this feature can have a great influence on the non-radiative process. Furthermore, based on these theoretical predictions, experimental verifications are performed and the synthesized BPCN-2spAs is confirmed to be an efficient NIR TADF molecule. Thus, the relationships between basic molecular structures and photophysical properties are revealed, a feasible design strategy is applied and four promising red and NIR TADF molecules are proposed. All these results could contribute to the development of red and NIR TADF emitters and OLEDs.

Protein profile analysis of tear fluid with hyphenated HPLC-UV LED-induced fluorescence detection for the diagnosis of dry eye syndrome.

Tear fluid contains organic and inorganic constituents, variations in their relative concentrations could provide valuable information and can be useful for the detection of several ophthalmological diseases. This report describes the application of the lab-assembled light-emitting diode (LED)-based high-performance liquid chromatography system for protein profiling of tear fluids to diagnose dry eye disease. Principal Component Analysis (PCA), match/no-match, and Artificial Neural Network (ANN) based binary classification of protein profile data were performed for disease diagnosis. Results from the match/no-match test of the protein profile data showed 94.4% sensitivity and 87.8% specificity. ANN with the leaving one out procedure has given 91.6% sensitivity and 93.9% specificity.

LiBa12(BO3)7F4 (LBBF) crystals doped with Eu3+, Tb3+, Ce3+: structure and luminescence properties.

The luminescent properties of single crystals and polycrystalline samples of LiBa12(BO3)7F4 (LBBF) doped and co-doped with Eu3+, Tb3+, and Ce3+ have been studied in order to disclose their potential for application in white light-emitting diodes. Deciphering of LBBF:Eu3+ crystal structure (P42/mbc) makes it possible to determine the scheme of heterovalent isomorphic substitution 3Ba2+ ← 2Eu3+ + □, □ - vacancy in barium sites. Luminescent properties of LBBF crystals co-doped with Eu3+, Tb3+, Ce3+ and Eu3+, Tb3+ are compared. Both crystals demonstrate the luminescence close to day light with CIE coordinates and correlated color temperature (0.280; 0.305), 9232 K for LBBF:Eu3+,Tb3+,Ce3+ and (0.353; 0.390), 4849 K for LBBF:Eu3+,Tb3+ at 300 K at 370 nm excitation. The study of polycrystalline samples LBBF:Ce3+, LBBF:Tb3+, and LBBF:Eu3+, using X-ray diffraction, shows that the homogeneity regions of solid solutions differ significantly. In solid solutions LBBF:Tb3+ and LBBF:Eu3+, a gradual change in symmetry in the "tetragonal → orthorhombic → tetragonal" series takes place as the concentration of the dopant increases. When excited at a wavelength 395 nm, LBBF:Eu3+ samples with the content of Eu3+ 0.5 wt% and 2 wt% demonstrate intense red light with a high quantum yield of 63 and 60%, respectively, which allows them to be used as red components of composite phosphors for white LEDs.

Pioneering research on blue "hot exciton" polymers and their application in solution-processed organic light-emitting diodes.

An innovative novel category of polymeric hybridized local and charge-transfer (HLCT) blue materials prepared via solution processing has yet to be reported. This study introduces three polymers, namely PZ1, PZ2, and PZ3, incorporating donor-acceptor-donor (D-A-D) structures with carbazole functioning as the donor and benzophenone as the acceptor. To regulate the luminescence mechanism and conjugation length, carbonyl and alkyl chains are strategically inserted into the backbone. Theoretical calculation and transient absorption spectroscopy illustrate that the robust spin-orbit coupling between high-lying singlet excited states (Sm: m ⩽ 4) and triplet excited states (Tn: n ⩽ 7) of the polymers hastens and significantly heightens the efficiency of reverse intersystem crossing processes from Tn states. Furthermore, the existence of multiple degenerated frontier molecular orbits and significant overlaps between Tn and Sm states give rise to added radiative pathways that boost the radiative rate. This study marks a fundamental and initial manifestation of HLCT materials within the polymer field and provides a new avenue for the design of highly efficient polymeric emitters.

Uniform nucleation and growth of Cs3Cu2I5 nanocrystals with high luminous efficiency and structural stability and their application in white light-emitting diodes.

Copper-based ternary halide composites have attracted great attention due to their superior chemical stability and optical properties. Herein, we developed an ultrafast high-power ultrasonic synthesis strategy to realize the uniform nucleation and growth of highly luminescent and stable Cs3Cu2I5 nanocrystals (NCs). The as-synthesized Cs3Cu2I5 NCs show uniform hexagonal morphology with an average mean size of 24.4 nm and emit blue light with a high photoluminescence quantum yield (PLQY) of ∼85%. Moreover, the Cs3Cu2I5 NCs exhibit a remarkable stability during continuous eight times heating/cooling cycling tests (303-423 K). We also demonstrated an efficient and stable white light-emitting diode (WLED) with a high luminous efficiency (LE) of 41.5 lm W-1 and a Commission Internationale de l'Eclairage (CIE) color coordinate of (0.33,0.33).

Excellent yellow emission of Si3N4:Eu nanorods derived from waster silicon with better thermal stability for white LEDs

The core issue of light emitting diodes (LEDs) for actual application is the thermal stability of phosphors. Silicon nitride (Si 3 N 4 ) is generally recognized as especially important structural material due to its excellent mechanical properties at extreme high temperature. In this work, Si 3 N 4 : Eu was demonstrated to be an excellent luminescence functional material for LEDs. The discarded corner-waster silicon raw material was utilized to act as the precursor. The Si 3 N 4 :Eu phosphor was synthesized by a facile nitriding process at elevated temperature. The pure α-Si 3 N 4 :Eu nanorods were successfully obtained by adjusting the doping concentration of Eu. It is coexistence with mixed-valence (divalent and trivalent) for Eu in α-Si 3 N 4 according to X-ray photoelectron spectroscopy. The synthesized α-Si 3 N 4 :Eu nanorods showed bright yellow under the excitation of 365 nm (UV) and white luminescence by 460 nm chip (Blue). The Si 3 N 4 :Eu nanorods possess excellent thermal stability, maintains nearly 70% of the origin intensity even at temperatures over 300 °C. The Si 3 N 4 :Eu nanorods demonstrated comparable performance to commercial YAG:Ce 3+ (YAG). Moreover, the long-term thermal stability of Si 3 N 4 :Eu nanorods is superior to commercial YAG, revealing the enhanced service performance. This work not only presents a facile Si 3 N 4 :Eu nanorods green synthesis route from waste utilization, but also offers an enhanced service performance for the high temperature LEDs application.

Impact of core-shell perovskite nanocrystals for LED applications: successes, challenges, and prospects.

Perovskite nanocrystals (PeNCs) synthesized by colloidal solution methods are an outstanding case of study due to their remarkable optical features, different from their bulk counterpart, such as a tuneable band gap and narrower photoluminescence emission, altered by the size and shape. However, the stability of these systems needs to be improved to consolidate their application in optoelectronic devices. Improved PeNC quality is associated with a less defective structure, as it affects negatively the photoluminescence quantum yield (PLQY), due to the essential, but at the same time labile interaction between the colloidal capping ligands and the perovskite core. In this sense, it would be extremely effective to obtain an alternative method to stabilize the PeNC phases and passivate the surface, in order to improve both stability and optical properties. This objective can be reached exploiting the structural benefits of the interaction between the perovskite and other organic or inorganic materials with a compatible structure and optical properties and limiting the optical drawbacks. This perspective contemplates different combinations of core/shell PeNCs and the critical steps during the synthesis, including drawbacks and challenges based on their optical properties. Additionally, it provides insights for future light emitting diode (LED) applications and advanced characterization. Finally, the existing challenges and opportunities for core/shell PeNCs are discussed.

Comparative Evaluation of LED Light Application and Heat Generation with Three Different Wavelengths of Frequency on Soft Tissues in Bringing Faster Orthodontic Tooth Movement: A Finite Element Model Study.

The duration of orthodontic treatment is often a significant deterrent for patients when considering conventional mechanics, which can be time-consuming. Photobiomodulation (PBM) utilizes visible red to near-infrared wavelengths of light frequencies to expedite orthodontic treatment time. To investigate the effect of three Light Emitting Diode (LED) frequencies and their heat generation on soft tissues in accelerating tooth movement through Finite Element Method (FEM) study. In this FEM study, a three-dimensional FEM model of the skull of a male patient with mild to moderate crowding in the maxilla, and mandible. The dentitions were scanned using a Computed Tomography (CT). A static force of 70 gm on the anterior region of the maxilla and mandible was applied from the labial sides, and a second static analysis was carried out by using both a 70 gm of force and thermal load with three different frequencies of 740, 850, and 940 nm on the 1st and 3rd quadrants. The effect of LED application and heat generation was assessed on soft tissues in bringing faster orthodontic tooth movement. Increased tooth movement with combined loading case in the 1st and 3rd quadrants when compared with the 2nd and 4th quadrants. The temperature distribution was higher at 940 nm followed by 740 & 850 nm of frequency. Faster movements were observed in the combined loading case in the 1st and 3rd quadrants compared to static loading in other quadrants. Heat generation was higher with 940 nm frequency followed by 740 and 850 nm.

Composition and structure regulation of Ruddlesden–Popper perovskite for light-emitting diodes applications

Ruddlesden–Popper (RP) perovskites have gained increased attention for LED applications due to their tunable band gap, enhanced stability, and excellent charge transfer. We summarize four methods to improve the properties of RP perovskites.

One-pot reaction derived multicolor nitrogen-doped graphene quantum dots for LED applications

Multicolor nitrogen-doped graphene quantum dots (NGQDs) were prepared via one-pot method and purified by column chromatography to obtain three NGQDs with different emission colors, i.e. blue emission (B-NGQDs), cyan emission (C-NGQDs), and yellow emission (Y-NGQDs). The multicolor NGQDs were combined with InGaN chip to fabricate light-emitting diode (LED) that emitted blue, cyan, and yellow light, respectively. Moreover, reducing the amount of Y-NGQDs used could construct a white LED (WLED) with color coordinate of (0.324, 0.334).

Layer-dependent structure-optoelectronic property relationships for two-dimensional ruddlesden-popper phase (BA)2Csn−1PbnBr3n+1 perovskites

Recently, hybrid two-dimensional (2D) Ruddlesden-Popper (RP) phase layered halide perovskite structures of (BA)2Csn-1PbnBr3n+1 (BA is the butylammonium organic chain and n is the number of inorganic perovskite-like layers) have been experimental synthesized and indicated superior optical properties. Here, we reported an investigation of the above series of layered halide perovskites (n = 1, 2, 3 and ∞). Their structural, electronic and optical properties were calculated using first-principle approaches, including the bond angles, band structures, formation energy, carrier effective masses, density of states, differential charge densities, Bader charge analysis, optical absorption spectra and transition dipole moment. As a consequence of these findings, with the increase in the number of inorganic layers, perovskite materials showed lower bandgaps, improved light absorption and poorer stability. Hence, tuning the inorganic layer thickness of layered 2D RP phase perovskites is a suitable method to enhance their optoelectronic properties. This work provides a theoretical basis for layered 2D perovskite materials with large-scale and low-cost applications in the photoluminescent device light-emitting diodes.