Blue-emitting Chip Research Articles

Realize short-wave infrared luminescence in NaScP2O7:Cr3+,Yb3+ phosphor: Spectral and energy transfer

Short-wave infrared emitting phosphors have extensive applications for spectroscopy technology. The near-infrared phosphor NaScP2O7:Cr3+ that we present in this work has a full width at half maximum (FWHM) of approximately 196nm, which ranges from 700 to 1200nm. To achieve efficient short-wave infrared, Yb3+ ions were co-doped. The NaScP2O7:Cr3+,Yb3+ material emitted infrared bands with peaks at 970 and 1003nm upon excitation at450nm. Benefitting from energy transfer (ET), the light in the 900-1200nm from Yb3+ is effectively enhanced. Photoluminescence spectra, thermal quenching, and decay curves of Cr3+/Yb3+ single and codoped NaScP2O7 were investigated. An internal quantum yield of 29.6% wasdemonstrated by the optimized phosphor NaScP2O7:Cr3+,Yb3+. Furthermore, The final fabrication of the short-wave infrared pc-LED was done through the combination of a blue-emitting chip and NaScP2O7:Cr3+,Yb3+ phosphor, thereby showing great promise for real implementations.

Early failure of high-power white LEDs for outdoor applications under extreme electrical stress: Role of silicone encapsulant

Early failure of high-power white LEDs for outdoor applications under extreme electrical stress: Role of silicone encapsulant

A fully π-conjugated triazine-based 2D covalent organic framework used as metal-free yellow phosphors in white light-emitting diodes

Luminescent covalent organic frameworks (COFs) can be used as metal-free phosphors to replace rare earth-based phosphors for LEDs. Here, a fully π-conjugated 2D COF containing triazine units is synthesized via Knoevenagel condensation by using terephthalaldehyde (TPA) and 2,2',2''-((1,3,5-triazine-2,4,6-triyl)tris([1'',1'''-biphenyl]-4',4''-diyl))triacetonitrile (TTTA) as monomers. This yellow-emitting COF consists of a periodic hexagonal pore structure and is in an eclipsed (AA) stacking mode. Its solid-state photoluminescence quantum yield (PLQY) is 26.0%, its thermal decomposition temperature (Td) is ca. 495 °C, and its relative emission intensity at 90 ℃ is 80.0% of that at 30 °C, at 150 ℃ is 58.9% of that at 30 °C. Together with GaN-based blue-emitting chips (λem,max ≈ 460 nm, around 25.0 lm·W-1), a series of cold/neutral/warm white LEDs are fabricated by using the COF as yellow phosphors at different concentrations in epoxy resin. At 2.0 wt.%, a cold white LED is obtained with the best performances, its correlated color temperature (CCT) is 5743 K, color rendering index (CRI) is 83.1, Commission Internationale de L’Eclairage (CIE) chromaticity coordinate is (0.33, 0.29), luminous efficacy (LE) is 18.18 lm·W-1.

Aggregation-Induced Emission Metallocuboctahedra for White Light Devices.

Materials for organic light-emitting devices which exhibit superior emission properties in both the solution and solid states with a high fluorescence quantum yield have been extensively sought after. Herein, two metallocages, S1 and S2, were constructed, and both showed typical aggregation-induced emission (AIE) features with intense yellow fluorescence. By adding blue-emissive 9,10-dimethylanthracene, pure white light emission can be produced in the solution of S1 and S2. Furthermore, due to the remarkable AIE feature and good fluorescence quantum yield in the solid state, metallocages are highly emissive in the solid state and can be utilized to coat blue LED bulbs or integrate with blue-emitting chips to obtain white light. This study advances the usage of metallocages as practical solid-state fluorescent materials and provides a fresh perspective on highly emissive AIE materials.

Multifunctional behavior of a carbazole derivative: Red phosphorescent emission, aggregation-induced long-life exciton and light-emitting diode application

A D-π-A typed cyanyl-carboxylic derivative (named as CECZA) merely produced prompt fluorescence with lifetime at nanosceond scale in dilute solutions, whose solid-state luminescence exhibited 3.36μs lifetime with 13.80% quantum yield (QY, captured at 522nm for powder at nanometer scale) at 298K and 43.36ms lifetime with 30.46% QY (650nm, 80K, tiny crystals). Femtosecond transient absorption, Raman spectroscopy and quantum chemical calculation provided valid clues to reveal its excitonic transition mechanism. The results indicated that the restricted vibration of benzene ring on carbazole group and alkyl chain weakened the vibrational modes of CECZA molecule and strengthened inter-molecular interactions between adjacent molecules at low temperatures, which promoted the persistent phosphorescent emission. Due to strong UV-vis absorption, high quantum efficiency and excellent thermal stability, CECZA can be used as a potential candidate in light-emitting diode (LED) application. Combined with a commercial InGaN blue-emitting chip, CECZA-InGaN emitted daylight white light.

Site-Selective Occupancy Control of Cr Ions toward Ultrabroad-Band Infrared Luminescence with a Spectral Width up to 419 nm.

Infrared-emitting phosphor-converted light-emitting diodes (LEDs) are desirable light sources for a very wide range of applications such as spectroscopy analysis, nondestructive monitoring, covert information identification, and night-vision surveillance. The most important aspect of infrared emitters for spectroscopy is to cover the widest possible wavelength range of emitted light. However, developing ultrabroad-band infrared emitters based on converter technology is still a challenging task due to the lack of suitable phosphor materials that emit in a wide wavelength range upon excitation from blue-emitting chips. Herein, this work demonstrates Cr3+-activated Mg2SiO4 infrared phosphors with a super wide infrared spectral range of 600 to 1400 nm and high internal quantum yield up to 80.4% upon 460 nm excitation. Site-selective occupancy of Cr3+ emitters in two different Mg sites in the Mg2SiO4 lattice results in two distinct broad emission bands peaking at 760 and 970 nm, both of which contribute to the ultrabroad-band infrared luminescence with a full width at half maximum (FWHM) of 419 nm. This is by far the broadest infrared emission to the best of our knowledge. On this basis, an ultrabroad-band infrared LED prototype has been fabricated by the combination of the Mg2SiO4:Cr3+ phosphor with a blue LED chip, which shows great potential for imaging and sensing applications. This work demonstrates that site-selective occupancy control of Cr ions is an effective strategy for developing ultrabroad-band Cr3+-doped phosphors.

High water resistance and luminescent thermal stability of organic-inorganic hybrid K2SiF6:Mn4+ red emitting phosphor induced by a multi-dentate ligand

Mn 4+ -activated fluoride is a kind of high-efficiency red-emitting phosphor widely used in WLEDs (white light-emitting diodes). However, the poor moisture resistance hampers their commercial application on a large scale. Here, a new type of organic-inorganic hybrid KSF:HMTA, Mn 4+ (KSF:K 2 SiF 6 , HMTA: hexamethylenetetramine) red-emitting phosphor has been prepared through the cation exchange method. Compared with KSF:0.04Mn 4+ , emission intensity, florescent thermal stability, and water resistance of KSF:HMTA,0.04Mn 4+ are improved significantly due to the formation of MOF (metal-organic framework) between HMTA and K 2 MnF 6 . MOF creates an antenna effect and forms an insoluble protective shell on the sample surface. The former induces the negative thermal quenching (NTQ) effect via phonon-excited electron interaction, significantly improving the florescent thermal stability. The latter prevents the contact of Mn 4+ ions on the sample surface with water molecules, resulting in enhancement of waterproofness. The formation mechanism of the MOF was discussed. A prototype WLED with warm white light ( CCT = 3815 K and Ra = 90.4) were assembled via coating a mixture of YAG:Ce 3+ , KSF:HMTA,0.04Mn 4+ and epoxy resin on a blue-emitting chip (450 nm). The results show that KSF:HMTA, 0.04Mn 4+ is a potential red-emitting phosphor that can be used on its part of WLEDs. • KSF:HMTA, Mn 4+ has been synthesized. • Sample has high water resistance, thermal stability and luminescent intensity. • Water resistance, thermal stability and emission intensity are enhanced by formation of MOF. • The negative thermal quenching is attributed to the increase of suitable electron traps.

A sp2-carbon-linked covalent organic framework containing tetraphenylethene units used as yellow phosphors in white light-emitting diodes

A sp 2 -carbon-linked covalent organic framework (COF) containing tetraphenylethene units was successfully synthesized by using 2,2'-(1,4-phenylene)diacetonitrile and 4′,4‴,4‴'',4‴''''-(Ethene-1,1,2,2-tetrayl)tetrakis(([1,1′-biphenyl]-4-carbaldehyde)) as monomers. After being investigated by powder X-Ray diffraction (PXRD), nitrogen adsorption-desorption and theoretical calculations, the dual-pore eclipsed Kagome structure (AA-K) of the COF was confirmed. The COF emitted bright yellow light with a solid-state photoluminesce quantum yield (PLQY) of 39.2%. It exhibited high thermal stability with a thermal decomposition temperature ( T d ) of ca. 610 °C, and its relative emission intensity at 90 °C was nearly 80.0% of that at 30 °C. The COF was blended in epoxy resin at different concentrations and used as phosphors, excited by GaN-based blue-emitting chips (λ em,max ≈ 455 nm), a series of white light-emitting diodes (WLEDs) with different correlated color temperature (CCT) can be obtained. At 1.5 wt%, a cold WLED was obtained, its CCT was 6125 K, color rendering index (CRI) was 83.4, Commission Internationale de L'Eclairage (CIE) chromaticity coordinate was (0.32, 0.29), luminous efficiency ( η L ) was 20.31 lm·W −1 . At 2.0 wt%, a neutral WLED was obtained, its CCT was 4293 K, CRI was 79.6, chromaticity coordinate was (0.36, 0.34) and η L was 19.71 lm·W −1 . At 2.5 wt%, a warm WLED was obtained, its CCT was 3348 K, CRI was 69.4, chromaticity coordinate was (0.42, 0.42) and η L was 18.81 lm·W −1 . The results suggested the COF can be used promising metal-free phosphors in WLEDs. • A sp 2 -carbon-linked covalent organic framework (COF) containing tetraphenylethene units was synthesized. • The COF emitted bright yellow light with a solid-state photoluminesce quantum yield (PLQY) of 39.2%. • The thermal decomposition temperature ( T d ) of the COF was as high as 610 °C. • Cold/neutral/warm white LEDs with high performances were prepared by using the COF and blue-emitting chips.

One-pot synthesis of metal-free, yellow-emitting phosphor with organic single crystal as a matrix

In recent years, there is a rapid growth on the research of metal-free phosphor. A typical example is blend of photoluminescent carbon nanomaterials with a matrix. Normally, the C dots were prepared first, which were then mixed with the matrix. A drawback of this strategy is that multiple steps have to be involved, which is time consuming. In this work, we show that by simply heating a readily-available small organic molecule (phthalic acid) in a high-boiling solvent with reactive group (formamide), ready-to-use and metal-free phosphor can be produced in high yields (over 70%). The phosphor contains single crystals of phthalic anhydride with photoluminescent species adsorbed on the surfaces, which shows yellow emission in solid state with a fluorescence quantum yield ( Φ ) of 28.53%. The phosphor can be directly used to prepare light-emitting diodes (LEDs), which results in a yellow LED on the UV chip and a white LED on the blue-emitting chip. Single crystals of small organic molecules with carbon dots adsorbed on the surface have been prepared. The hybrid material shows yellow emission, which can be used as metal-free phosphor for white-light-emitting diodes. • Metal-free phosphor can be readily prepared in one-step with high yield. • The phosphor can be directly used to prepare LEDs. On the blue-emitting LED chip, a white LED was obtained. • The as-prepared crystals exhibit strong emission in both solid and colloidal state.

Novel yellow solid-state fluorescent-emitting carbon dots with high quantum yield for white light-emitting diodes

Fluorescence quenching of carbon dots (CDs) occurs in their aggregated state ascribed to direct π-π interactions or excessive resonance energy transfer (RET). Thus, CDs have been severely restricted for applications requiring phosphors that emit in the solid state, such as the fabrication of white light-emitting diodes (WLEDs). In this report, novel CDs with bright solid-state fluorescence (SSF) were synthesized by simple microwave-assisted synthesis method, using 1,4,7,10-tetraazacyclododecane (cyclen) and citric acid as precursors. Under 365nm UV light, these CDs emit bright yellow SSF, indicating they successfully overcome the aggregation-induced fluorescence quenching (ACQ) effect. When the excitation wavelength (λex) is fixed at 450nm, the emission peak of the CDs is centered at 546nm with the Commission Internationale de l'Eclairage chromaticity (CIE) coordinates of (0.43, 0.55), which means that they can be combined with a blue-emitting chip in order to fabricate WLEDs. More importantly, the absolute quantum yield (QY) of these CDs powder reached 48% at λex of 450nm, which was much higher than many previously reported SSF-emitting CDs and indicating their high light conversion ability in solid-state. Thanks to the excellent optical property of these CDs powder, they were successfully used in the preparation of high-performance WLEDs. This study not only enriches SSF-emitting CD-based nanomaterials with good prospects for application, but also provides valuable reference for subsequent research on the synthesis of solid-state fluorescent CDs.

Greenish-yellow emitting Ca9MgLi(PO4)7:Dy3+ phosphors – Photoluminescence and thermal stability

Abstract In this work, the photoluminescence features, decay lifetime, internal quantum yield, and thermal stability of whitlockite structured phosphors of Ca9MgLi(PO4)7:Dy3+ were investigated. The phosphor exhibit the capability of being efficiently excited by near-UV (350, 364, 387 nm) and blue light (451 nm), exhibiting the characteristic greenish-yellow emission with two strong peaks at 487 and 577 nm, ascribing to the transitions of 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2, respectively. The phosphor synthesized using a conventional solid-state reaction method at 1350 °C also show high phase purity with good compositional homogeneity and crystallinity. The Ca9MgLi(PO4)7:0.1Dy3+ phosphor showed the optimal photoluminescence emission intensity and quantum yield. The electronic transition mechanism is direct exchange interaction between activators, contributing to the concentration quenching. The phosphor was able to retain 67% of its intensity without significant colour change at an elevated temperature up to 300 °C. This work illustrates the potential of Ca9MgLi(PO4)7:Dy3+ phosphors for the application in white LED devices pumped with an n-UV or blue-emitting chip.

Enabling Warm-White LEDs with Very High Luminous Efficacy By Use of Uranyl Sensitized Eu3+

Warm-white light emitting diodes require a red emitting phosphor to provide sufficient emission in the red spectral region. Currently, Eu2+ activated nitrides and Mn4+ activated fluorides are state-of-the-art compounds [1,2]. Both materials have significant disadvantages: Divalent europium in nitrides suffers from a broad emission band that reaches into the NIR which strongly decreases the luminous efficacy. The synthesis of fluoride hosts for Mn4+ involves toxic hydrofluoric acid and their chemical stability is limited due to the oxidative properties of Mn4+ towards F-. Thus, Eu3+ presents an interesting alternative. Very high luminous efficacy and excellent thermal and chemical stability can be achieved in easily accessible oxide hosts [3]. However, the low absorption cross section in the UV-B to visible spectral range hinders the application of Eu3+ in warm-white LEDs. Approaches to overcome this limitation include, among others, excitation via charge transfer bands [4], sensitization with Tb3+ [5], or the use of Ce/Tb comprising core/shell materials [6]. Nonetheless, there have been no reports of successful implementation of a Eu3+ activated phosphor on a blue emitting LED chip so far. As a novel approach we chose the uranyl cation to sensitize Eu3+. While the energy transfer from uranyl to Eu3+ is well known, it has not been utilized thus far to enable Eu3+ activated red emitting LED phosphors. One reason might be that uranium is usually perceived as a health hazard for its toxicity and radioactivity. However, the dose received from ingestion of 10 mg of depleted uranium (DU) amounts to merely 1 µSv (ICRP 72), which is lower than the dose received daily through natural radiation. Consequently, to date it has not been conclusively shown if DU is a carcinogen [7,8]. With an assumed LD50 of 5 g in humans, the chemical toxicity is comparable to that of cadmium which is used in quantum dots [9]. DU would be present on an LED in minute amounts of approximately 0.1 mg per chip. The number of suitable hosts, i.e. those exhibiting both a doping site for Eu3+ and comprising the uranyl cation, is comparatively low. We studied two different compounds, Eu(UO2)3(PO4)2O(OH)∙xH2O and K4Eu2(UO2)(Ge2O7)2. The phosphate suffers from quenching due to the presence of H2O and OH moieties. Exchange of H+ by D+ was successfully attempted to alleviate this problem [10]. The germanate possesses excellent properties, allowing us to manufacture a warm-white LED employing K4Eu2(UO2)(Ge2O7)2 as the red emitter. The LED shows an excellent luminous efficacy and color rendering index at a correlated color temperature of 2700 K. To the best of our knowledge this is the first LED comprising a blue-emitting chip and a red emitting Eu3+ phosphor [11].

Tunable WLED with UV chip based on all-inorganic perovskite quantum dots

Abstract Two major problems exist in tunable White Light-Emitting Diodes (WLEDs) that are typically composed of blue-emitting chip, yellow- and/or red-emitting phosphors: (1) the unstable hue of blue-emitting chip, and (2) the harsh conditions (such as high reaction temperature and reductive atmosphere) of traditional red-emitting phosphors. In this paper, we explore a sandwich layer WLEDs structure of ITO (Indium Tin Oxide) films + blue-, yellow- and/or red-emitting pervoskite QDs phosphors + UV-emitting chip to solve the issues. Through changing the number of layers of the three QDs, the correlated color temperature (CCT) was tuned from 8658 to 3961 K, indicating the WLED tuning from cool to warm light.

Nanostructured NdF3 glass ceramic: An efficient bandpass color filter for wide-color-gamut white LED

Abstract Up-to-date LED-lit LCD technology pursues a wide color gamut to ensure reproduction of all natural colors. Herein, a novel NdF3 glass ceramic was developed as bandpass color filter for pc-wLEDs. In-depth microstructural and optical analyses reveal the alteration of local environment of Nd3+ from the oxide-amorphous matrix to the fluoride-crystalline phase after crystallization. A prototype pc-wLED is constructed by coupling all-inorganic “YAGG:Ce3++CASN:Eu2+” phosphor-in-glass plate and NdF3 glass ceramic plate with blue-emitting chip in a stacked configuration. Thanking to the efficient absorption from hypersensitive Nd3+: 4I9/2 → 4G5/2, 2G7/2 transition, the electroluminescent spectral profile of phosphors can be well separated into two narrowed bands in the green and red regions, and so an improved color gamut of 78.8% is achieved. The present work demonstrates an efficient route for wide-color-gamut white LED in a facile and cost-effective way.

Synthesis and Luminescence Properties of CsPbX3@Uio-67 Composites toward Stable Photoluminescence Convertors.

All-inorganic halide perovskite (CsPbX3, X = Cl, Br, or I) nanocrystals (NCs) have been widely studied due to their outstanding optoelectronic properties. However, some inevitable factors like light, heat, and moisture affected the stability of CsPbX3 NCs and further limited their practical application. In this work, the stability of all-inorganic halide perovskite NCs can be improved by integrating them in the stable Zr-based metal-organic frameworks (Uio-67). Compared to pristine perovskite NCs, typical CsPbBr3@Uio-67 composites display a stable photoluminescence property that can be maintained for 30 days under ambient atmospheric conditions. Due to the proposed confinement effects of CsPbX3 NCs coordinated with the pore structures of Uio-67, the related structural model of CsPbX3@Uio-67 composites was elucidated. White LED device was further fabricated by combining CsPbBr3@Uio-67 composites and commercial K2SiF6:Mn4+ red phosphors with a blue-emitting chip, which demonstrated a wide color gamut (138% of National Television Standards Committee color space). The strategy on encapsulation of CsPbX3 NCs into Uio-67 will open up a stable platform for optoelectronic applications.

Preparation and luminescent performances of transparent screen-printed Ce3+: Y3Al5O12 phosphors-in-glass thick films for remote white LEDs

Ce3+: Y3Al5O12 (Ce-YAG) phosphors-in-glass (PiG), which serves as both luminescent convertor and encapsulating material in the remote white light-emitting diodes (LEDs), has become a promising research field. However, the challenges in processing and mechanical strength still remain due to its submillimeter thickness. Herein, a novel transparent Ce-YAG PiG thick film was coated on a common glass substrate through conventional screen printing process and subsequent heat treatment. The introduced commercial Ce-YAG phosphors almost kept intact in a lead-free glass matrix. The microstructures and luminescent properties of as-prepared samples were investigated systematically. White LED device was also fabricated via mounting the optimal sample on the InGaN blue-emitting chips, which yielded bright white light with considerable luminous efficiency and color quality. The resulting screen-printed Ce-YAG PiG thick film will be a promising candidate for applications in the high-power remote white LEDs.

ChemInform Abstract: A Review on Mn4+ Activators in Solids for Warm White Light‐Emitting Diodes

AbstractReview: 80 refs.

Effect of Lu<sub>3</sub>Al<sub>5</sub>O<sub>12</sub>:Ce<sup>3+</sup> and (Sr,Ca)AlSiN<sub>3</sub>:Eu<sup>2+</sup> Phosphor Content on Glass Conversion Lens for High-Power White LED

Currently, the majority of commercial white LEDs are phosphor converted LEDs made of a blue-emitting chip and YAG yellow phosphor dispersed in organic silicone. However, silicone in high-power devices results in long-term performance problems such as reacting with water, color transition, and shrinkage by heat. Additionally, yellow phosphor is not applicable to warm white LEDs that require a low CCT and high CRI. To solve these problems, mixing of green phosphor, red phosphor and glass, which are stable in high temperatures, is common a production method for high-power warm white LEDs. In this study, we fabricated conversion lenses with LUAG green phosphor, SCASN red phosphor and low-softening point glass for high-power warm white LEDs. Conversion lenses can be well controlled through the phosphor content and heat treatment temperature. Therefore, when the green phosphor content was increased, the CRI and luminance efficiency gradually intensified. Moreover, using high heat treatment temperatures, the fabricated conversion lenses had a high CRI and low luminance efficiency. Thus, the fabricated conversion lenses with green and red phosphor below 90 wt% and 10 wt% with a sintering temperature of 500℃ had the best optical properties. The measured values for the CCT, CRI and luminance efficiency were 3200 K, 80, and 85 ㏐/w.

Synthesis, composition optimization, and tunable red emission of CaAlSiN3:Eu2+ phosphors for white light-emitting diodes

Abstract

Advances in transparent glass–ceramic phosphors for white light-emitting diodes—A review

Abstract Currently, the major commercial white light-emitting diode is the phosphor converted LED made of blue-emitting chip and Y 3 Al 5 O 12 :Ce 3+ yellow phosphor dispersed in organic silicone. However, the organic binder in high-power device ages easily and turns yellow due to accumulated heat emitted from chip, which adversely affects the device properties such as luminous efficacy and color coordination, and therefore reduces its long-term reliability as well as lifetime. In this mini-review article, we provide an overview of recent progresses in developing transparent inorganic glass–ceramics phosphors excitable by blue chip, as an alternative to conventional polymer-based phosphor converter, for construction of high-power white light-emitting diodes. Two kinds of synthesis routes, glass crystallization and low-temperature co-sintering, are discussed in detail. Afterwards, the materials design, structure/property optimization as well as glass–ceramic-based WLED devices construction are summarized. Finally, challenges and future advances for the realization of transparent glass–ceramics in commercial applications will be presented.