LED Encapsulation Research Articles

Predicting Photocatalytic Properties of Metal Coupled Mn-TiO2 Particle Using Response Surface Methodology (RSM) as a Potential Filler in LED’s Encapsulant

This study addresses yellowing discoloration in LEDs caused by TiO2 particle degradation in encapsulants. The commonly added TiO2 particles will enhance light reflectance, and accelerate photodegradation but will decrease LED lifespan by lowering lumen quality and causing chromaticity change. To mitigate these effects, Mn particles were coupled with TiO2 particles using photo-reduction. This research examined three parameters Mn2+ ions concentration, UV irradiation duration, and annealing temperature, and the successful Mn-TiO2 coupling achieved. The resulting Mn-TiO2 particles, synthesized at 20 ppm Mn2+ ions and 200 °C annealing temperature, exhibited superior dispersibility and minimal agglomeration compared to TiO2 particles. Next, the photocatalytic performance of Mn-TiO2 particles was optimized using Response Surface Methodology (RSM). These particles exhibited the lowest photodegradation with a rate constant of 0.03092 min−1 and achieved a photodegradation efficiency of 79.92% at 60 min, amongst the others. Photodegradation of methylene blue followed a 1st-order kinetic model. Despite a slightly higher refractive index (RI), epoxy thin films with Mn-TiO2 particles displayed higher transmittance. Mn-TiO2 particles can thus serve as fillers in LED encapsulants to increase RI, reduce photodegradation, and enhance TiO2 particle dispersion. Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Visible to ultraviolet C (UVC) up-conversion of Er[formula omitted] doped yttrium aluminium garnet phosphor: Antimicrobial application

In the present work, a visible to ultraviolet C (UVC) up-conversion Er3+ doped yttrium aluminium garnet (YAG) ceramic phosphor was developed by a high temperature solid state reaction method. The structural characterization of the prepared phosphor was carried out using X-ray diffraction analysis and transmission electron microscopy techniques. The up-conversion behaviour of the phosphor was studied by recording the emission spectra of the phosphor under a 460 nm blue LED source. The emission spectrum was obtained in the UV region containing peaks centred at 217, 256, 275 and 312 nm. The emitted UV radiation belongs to the germicidal UV wavelength; therefore this behaviour of the phosphor was applied for the inactivation of surface born microbes through the emitted radiation. The emission behaviour of the phosphor was further investigated by LED encapsulation. The up-conversion emission increases with an increase in the crystal size.

A Hydrogen-Containing Di-Phenyl Siloxane Cross-Linker for Ultra-High Hardness and High Refractive Index Silicone Resin and its Application in LED Encapsulation

A Hydrogen-Containing Di-Phenyl Siloxane Cross-Linker for Ultra-High Hardness and High Refractive Index Silicone Resin and its Application in LED Encapsulation

Design and analysis of novel high-performance III-nitride MQW-based nanowire white-LED using HfO2/SiO2 encapsulation

A novel, white light-emitting diode structure with improved thermal characteristics is designed for providing efficient light which may be used especially in the underground mining environment. It describes a new nano hafnium oxide-silica doped silicone layer as LED encapsulation material that promises enhanced efficiency by 30.1% and reduced efficiency droop of 0.491%. The enhanced power and efficiency of the LED with HfO2/SiO2 doped bi-layer are attributed to the significant minimization of overflow of electrons which is fundamentally responsible for efficiency degradation through p-GaN region. In this article encapsulant material based on nano HfO2/SiO2 not only enhances light extraction but opens a broad new range of encapsulant engineering capabilities composites. Our designed LED is generated from a monolithic composition of blue and yellow spectrum which eventually creates the white light. This minimizes the problems related to multiple numbers of LEDs, green gap and phosphor color rendering.

Enhancing Optical Performance for White Light-Emitting Diodes Using Quantum- Dots/Boron Nitride Hybrid Reflective Structure

Quantum dots (QDs) are usually used with phosphor to obtain white light-emitting diodes (WLEDs) due to their excellent lighting characteristics. For lighting effect improvement, the QDs layer and the phosphor layer are supposed to be separated to reduce reabsorption loss and enhance QDs stability. Based on the separated structure, a QDs/boron nitride hybrid reflective (QBHR) structure is proposed to enhance the optical performance of WLEDs in this study. QDs were electrostatically bonded on the boron nitride (BN) pellets and their composite particles were subsequently mixed with silicone for LED encapsulation by a spinning-coated process. It could be easily managed the performance of QBHR structure by controlling the composite particles’ concentration or centrifugal speed. The diffuse reflectance and photoluminescence (PL) intensity of QBHR structure with various thicknesses were analyzed. While applying with remote phosphor layer for WLEDs, the luminous efficacy of devices with QBHR structure increases with phosphor concentration, which are larger than that of QD/polydimethylsiloxane (QP) structures. It may be caused by the light extraction ability of the scattering BN particles and high color conversion efficiency (CCE) of QBHR structure. Finally, under the same correlated color temperature (CCT) of 3640 K, the luminous efficacy and CCE enhance by 14.2% and 19.5% using the QBHR structure, respectively. In addition, the QBHR structure shows better stability than the QP structure after aging for 387.75 h. In brief, the QBHR structure shows an effective and practical packaging method to produce high-performance WLEDs.

Bioheat Model of Spinal Column Heating During High-Density Spinal Cord Stimulation

IntroductionHigh-density (HD) spinal cord stimulation (SCS) delivers higher charge per time by increasing frequency and/or pulse duration, thus increasing stimulation energy. Previously, through phantom studies and computational modeling, we demonstrated that stimulation energy drives spinal tissue heating during kHz SCS. In this study, we predicted temperature increases in the spinal cord by HD SCS, the first step in considering the potential impact of heating on clinical outcomes. Materials and MethodsWe adapted a high-resolution computer-aided design–derived spinal cord model, both with and without a lead encapsulation layer, and applied bioheat transfer finite element method multiphysics to predict temperature increases during SCS. We simulated HD SCS using a commercial SCS lead (eight contacts) with clinically relevant intensities (voltage-controlled: 0.5–7 Vrms) and electrode configuration (proximal bipolar, distal bipolar, guarded tripolar [+−+], and guarded quadripolar [+−−+]). Results were compared with the conventional and 10-kHz SCS (current-controlled). ResultsHD SCS waveform energy (reflecting charge per second) governs joule heating in the spinal tissues, increasing temperature supralinearly with stimulation root mean square. Electrode configuration and tissue properties (an encapsulation layer) influence peak tissue temperature increase—but in a manner distinct for voltage-controlled (HD SCS) compared with current-controlled (conventional/10-kHz SCS) stimulation. Therefore, depending on conditions, HD SCS could produce heating greater than that of 10-kHz SCS. For example, with an encapsulation layer, using guarded tripolar configuration (500-Hz, 250-μs pulse width, 5-Vpeak HD SCS), the peak temperature increases were 0.36 °C at the spinal cord and 1.78 °C in the epidural space. ConclusionsAs a direct consequence of the higher charge, HD SCS increases tissue heating; voltage-controlled stimulation introduces special dependencies on electrode configuration and lead encapsulation (reflected in impedance). If validated with an in vivo measurement as a possible mechanism of action of SCS, bioheat models of HD SCS serve as tools for programming optimization.

White emission from Dy3+ doped Gd2O3-B2O3 glass for WLEDs encapsulation

Novel bell-shaped glasses were fabricated to study the electro-luminescence properties of the glasses for LED applications. The physical and optical properties of Dysprosium (Dy3+) doped Gd2O3-B2O3 glasses were synthesised using the standard melt quenching procedure with compositions of 27.5Gd2O3-(72.5-x)B2O3-xDy2O3 (where x = 0.05, 0.1, 0.5, 1.0, and 1.5 mol%). The highest emission intensity of Dy3+ doped Gd2O3-B2O3 glasses was found to be at 0.5 mol% (by 275 nm excitaiton of Gd3+ ion) and 1.5 mol% (by 350 nm excitation of Dy3+ ion) of Dy2O3 concentration. A bright yellow emission corresponding to the transition F9/2→H13/2 (at 576 nm) was found in the emission spectra. This emission band was a mix of blue, yellow, and red. Furthermore, the CIE chromaticity diagram for glass 0.5 mol% Dy2O3 with color coordinates x = 0.368, y = 0.405, and shows white emission. The decay profiles were investigated for 575 emission and values show decreasing trend with increase in Dy2O3 content. Encapsulation of fabricated glasses were made to embed on top of the LED to investigate electro-luminescence spectra. From all results, this glasses could be used for LED encapsulation.

Synthesis of High Refractive Index Silicone LED Encapsulation with Ultra-High Hardness

Synthesis of High Refractive Index Silicone LED Encapsulation with Ultra-High Hardness

Facile thiol-epoxy click chemistry for transparent and aging-resistant silicone/epoxy composite as LED encapsulant

The thiol-epoxy click chemistry is promising for microelectronic packaging due to its outstanding properties, while there is little knowledge on silicone/epoxy composite fabricated via this approach. Herein, a thiol-functionalized silicone resin (MDT-SH) is synthesized and compounded with epoxy resin to form silicone/epoxy composite. The thermal-curing behaviors, mechanical properties and LED encapsulation of the developed composite are studied detailedly. The thermal-curing kinetics indicate that the thiol-epoxy polymerization in silicone/epoxy composite tends more to the first-order reaction and its active energy is about 60.3 kJ/mol. The mechanical properties of the composite are varied with the molecular structure of MDT-SH and thiol/epoxy ratio. Moreover, the composite has excellent transparency in visible region, and its transparency is little affected by thermal and UV ageing. More importantly, the transparency is only slightly decreased after the composite is serviced at normal temperature and pressure for 2 years. The light output power of LEDs encapsulated by this composite is comparable to the commercial counterparts like Dow Corning OE-6550, but its thermal-curing time and temperature are much lower than the latter, contributing to cost reduction. Therefore, this silicone/epoxy composite based on thiol–epoxy click chemistry would greatly improve the microelectronic packaging.

Synthesis of Epoxy-Modified Methyl Phenyl Silicone Resins for LED Encapsulation

The epoxy-modified silicones have the advantages of both epoxy and organic silicon. In this paper, a series of epoxy-modified methyl phenyl silicone resins were synthesized through the hydrosilylation reaction between 1, 2-epoxy-4-vinylcyclohexane and methyl phenyl silicone resins. The effects of catalyst dosage, reaction time and temperature on the products were further discussed to determine optimal reaction conditions. Then, the as-prepared epoxy-modified silicone resins were cured with methylhexahydrophthalic anhydride. The curing kinetics was investigated through differential scanning calorimetry (DSC). The curing conditions were determined as follows: 1-h curing at 80 °C for and subsequent 1-h curing at 110 °C. The as-prepared products exhibited high light transmittance (~ 90% at 450 nm), strong bonding, suitable hardness and sound waterproof performance. In addition, the introduction of methylphenylsiloxane chain significantly improved the heat resistance and UV resistance of cured products. The epoxy-modified silicone resins are ideal LED packaging materials.

Zirconia/phenylsiloxane nano-composite for LED encapsulation with high and stable light extraction efficiency.

To obtain a rapid processible LED encapsulant that leads to high and stable light extraction efficiency (LEE), UV curable ZrO2/phenyl-siloxane nano-composite (ZSC) double-layer encapsulants were prepared and optimized. The highly crystalline ZrO2 nanoparticles with a diameter of ∼14 nm were synthesized through a modified hydrothermal method at mild conditions, and a UV curable methacryl-diphenyl-polysiloxane (MDPS) with a refractive index (RI) of 1.54 (at 633 nm) was synthesized from self-condensation of diphenylsilanediol and an end-capping reaction. High refractive indexes (RIs) from 1.54–1.61 have been obtained for ZSC composites by adding 0–20 wt% ZrO2. Before and after sulfur vapor erosion, the double-layer encapsulated sample (M-10/M) showed 11.2% and 64.8% higher LEE respectively than that of Dow Corning OE-7662. Meanwhile, the variation of LED light color temperature (Tc) was less than 1%. The effect of the ZrO2 nanoparticle content on LEE of double-layer and single-layer encapsulation were compared and discussed based on Fresnel loss and Rayleigh scattering theories. The double-layered UV curing processing took only 1/6 of the time needed for common thermal curing.

A compact 2.0 T superconducting magnet.

A compact 2.0 T superconducting magnet has been developed for use in photoelectron microscopy. The magnet was required to be compact and magnetically well shielded with low stray fields. Because the magnet is for use with a microscope, the working volume can be small. A small volume implies that the stored magnetic energy is low, and with low stray fields, it makes the magnet safe while operating and during quench events. The magnet is a cryogen free design that uses a diamond loaded vacuum grease for current lead encapsulation and cooling. To make as small a coil as possible, a new coil winding method was developed that does not require solder joints between pancake windings. We show that a low temperature Sn/Bi/Ag eutectic solder can be used for connecting the input leads in this application.

Synthesis of siloxane oligomers containing boron and epoxy groups for promoting the adhesion of addition-curable silicone rubber to PPA and copper plate

The addition-curable silicone rubber (ASR) is a packaging material widely applied in the LED encapsulation. However, due to low surface energy, the silicone rubber has the poor adhesion to different substrates, such as copper and PPA. In this study, three silicone adhesion promoters, EBSiO, ESiO and BSiO were synthesized via non-hydrolytic dealcoholization reaction. The molecule structure of adhesion promoters was confirmed by infrared spectroscopy and gel permeation chromatography. The influences of three adhesion promoters on the adhesion performance of ASR were explored by shear strength tests. In addition, the transmittance of cured ASR with different additions of adhesion promoters was measured. The measurement results showed that the adhesion of cured ASR to metal copper and poly-phthalamide (PPA) was enormously enhanced by EBSiO in silicone rubber. After 1.0 phr EBSiO was added into silicone rubber, the adhesion strength between the obtained ASR and two materials (copper plate and PPA) respectively reached 3.163 MPa and 1.691 MPa, whereas the adhesion strength between the pristine ASR and two materials were respectively only 0.643 MPa and 0.474 MPa. The adhesion mechanism of cured ASR to PPA and copper was investigated. SEM images of the damaged interface between silicone rubber and substrates further proved that boron atoms and epoxy groups played an important role in enhancing the bonding performance of ASR to copper and PPA.

Preparation of Titanium-silphenylene-siloxane Hybrid Polymers with High Refractive Index, Transmittance, and Thermal Stability

Vinyl-containing titanium-silphenylene-siloxane oligomers (O1, O2, O3, and O4) with different molar ratios of titanium to silicon were successfully synthesized in high yields by nonhydrolytic sol-gel reaction, and the obtained four oligomers were further crosslinked with methylphenyl hydro-silicone oil (4) to form corresponding polymers (P1, P2, P3, and P4) by hydrosilylation reaction. Their structures were characterized with spectroscopic characterization techniques including FTIR, 1H-NMR, and Raman spectroscopy. The effect of titanium element on crosslinking behavior, thermal resistance, refractive index, transparency, thermal aging stability, glass transition temperature, and surface properties of the polymers were studied. Compared with titanium-free polymer P1, the thermal resistance, refractive index, and thermal aging stability of titanium-silphenylene-siloxane polymers (P2, P3, and P4) were significantly improved. The titanium-silphenylene-siloxane polymers achieved a high refractive index (n = 1.580–1.584) and thermostability (T5d > 500 °C). In thermal aging, the polymers exhibited superior performances with high optical transparency (~90% at 450 nm) and exhibited high thermal stability (~84% at 450 nm after thermal aging at 150 °C for 120 h). These data indicate that the polymers have potential application in optical materials such as LED encapsulants.

A New Dealcoholization Method in the Synthesis of Vinyl Methyl Phenyl Silicone Resins for LED Encapsulation

The oligosiloxane resins were synthesized through hydrolytic sol-gel reaction and remained many hydroxyl groups, which did great harm to the curing process and resulted in poor performance of the cured products. In previous works, epoxy-modified silicone resins were synthesized by dealcoholization, a reaction between 3-glycidoxypropylmethyldimethoxysilane and terminal hydroxyl groups in phenyl silicone resins. Although this method eliminated the hydroxyl groups, it caused a large loss of vinyl groups inevitably and a poor stability of cured products. In this study, methyltrimethoxysilane (MTMS) was used to eliminate hydroxyl groups containing in vinyl methyl phenyl silicone resins, which were synthesized through hydrolytic sol-gel reaction. Most of residual hydroxyl groups were deleted effectively and the great loss of vinyl groups were avoided in the dealcoholization reaction. Then, the methyl phenyl silicone materials were fabricated by hydrosilylation reaction between the synthesized vinyl methyl phenyl silicone resins and hydrogen-containing ones. The cured silicone materials showed excellent optical performance (~ 89.1% at 450 nm) and good adhesion performance. In addition, due to less vinyl loss in the vinyl methyl phenyl silicone resins, the cured methyl phenyl silicone materials exhibited higher cross-linking density, better thermal resistance (5% mass loss at 435 °C) and better mechanical properties (50 shore D) compared with the epoxy-modified phenyl silicone materials. The lumen depreciation (working 168 h at 50 mA) and reflow soldering tests further demonstrated the methyl phenyl silicone materials possessed good thermal stability. These results indicated that the methyl phenyl silicone materials could be used as a LED encapsulant with a good performance.

Perylene polyphenylmethylsiloxanes for optoelectronic applications

ABSTRACTThe incorporation of fluorescent organic dyes in an encapsulating matrix represents a route to generate stable and processable materials for optoelectronic devices. Here, we present a method to embed perylene dyes into a high refractive index (HRI) polysiloxane matrix applying an allyl functionalized perylene dye and hydrosilylation chemistry. In a first approach, the dye molecules were covalently integrated into the backbone of linear polyphenylmethylsiloxane chains. The fluorescent and liquid polymers were synthesized with molecular weights from 5660 up to 8400 g mol−1. In a second approach, the dye itself was used as a cross‐linking agent between linear polyphenylmethylsiloxane chains. These preformed fluorescent batch polymers are liquids with dye concentrations between 0.025 and 8 wt %. The applied synthetic methods incorporated the dye covalently into the polymer structure and avoided the crystallization of the dye molecules and thus the formation of excimers, which would reduce the optical emission. The resulting products can be easily incorporated into curable commercially available HRI polyphenylmethylsiloxane resins. The formed materials are ideal LED encapsulants with a solid and flexible consistency, a uniform dispersion of the dyes, and adjustable mechanical properties, realized by changing the amount of perylene polymers. Further properties of the obtained materials are thermal stabilities up to 478 °C, quantum yields larger than 0.97, and high photostabilities. Thus, the covalent integration of dyes into polyphenylsiloxane structures represents a possible route for the stabilization of the organic dyes against the extreme irradiance and thermal conditions in LED applications. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1062–1073

Crosslink network and phenyl content on the optical, hardness, and thermal aging of PDMS LED encapsulant

ABSTRACTThis work aims to synthesize new series of polysiloxane copolymer through hydrosilylation reaction based on different level of crosslink densities and phenyl content. The results revealed that polysiloxanes resins with phenyl rings increased viscosity up to 3800 cps while displaying a relatively high refractive index of 1.531. The asymmetric phenyl substitution onto chain backbone led to formation of densely packed structure resulting in reduced water absorption and gas permeability of PDMS resins. High level of crosslinking contributed to a high shore A hardness and adhesion strength. It displayed transparency of 97% whose percentage reduction was 1.6% under thermal and 0.6% UV aging. No obvious discoloration was observed during accelerated thermal aging up to 210 min at 80 °C. These results are key attributes that make the synthesized polysiloxane series as ideal candidate for high brightness LED encapsulant. © 2019 Wiley Periodicals, Inc. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47895.

Color-filtered phosphor-in-glass for LED-lit LCD with wide color gamut

Abstract In pursuit of wider color gamut to faithfully reproduce the fruitful natural colors has led the developing direction of LCD backlight technology. In this study, it is proposed a facile and cost-effective strategy based on a color-filtered phosphor-in-glass (PiG) which serves as LED encapsulant. It is demonstrated the green-/red-emitting YAGG:Ce3+/CASN:Eu2+ phosphors can be incorporated into Sn P F O glass matrix without altering their microstructural and luminescent properties significantly; while the introduced color-filter species, NdF3, experience a fluorine-rich environment due to interfacial F− diffusion from glass matrix. Utilizing the strong hypersensitive absorptions of Nd3+: 4I9∕2 → 4G5∕2; 2G7∕2 and 4I9∕2 → 4G7∕2 in the cyan and yellow regions, the electroluminescent green and red emission bands can be isolated from each other, which favors the widening of color gamut from 70.5% NTSC to 74.9% NTSC.

Platinum free thermally curable siloxanes for optoelectronic application - synthesis and properties.

Polysiloxanes for applications in the area of optical devices are usually based on two-component platinum catalysed cross-linked materials. Here we report the synthesis and properties of a novel one-component siloxane that can be thermally cured showing similar tailorable properties like commercially available encapsulation systems without using a noble metal catalyst. The pre-curing material is formed by an acid catalysed condensation reaction of trialkoxysilanes (TAS), dialkoxysilanes (DAS) and alkoxy-terminated polysiloxanes. NMR analysis of the formed polymeric compounds reveal that the materials are partially cross-linked gels. The obtained compounds can be thermally cured and consolidated at temperatures between 160 and 200 °C. Depending on the composition a tuneable hardness in between 50–90 Shore A, refractive indices of 1.494–1.505, as well as high temperature stabilities up to 443 °C were obtained. The high thermal- and photostability, the high transparency, as well as the tailorable refractive index makes these materials to ideal systems for optoelectronic applications. Investigations under increased temperatures and high-density illumination reveal that the material can withstand conditions, which are typical for high-performance light emitting diodes (LED).

An Efficient Process of Surface Modification and Patterning for LED Encapsulation

Encapsulation is a critical step in LED packaging to ensure good light extraction and protection. We present a novel mold-free process using a specific functionalization of the substrate to master the shape of the encapsulant dome. By controlling its aspect ratio, it is possible to increase light extraction. Experiments are correlated with Monte Carlo simulations to evidence the impact of surface tension on the dome shape as well as the effect of the refractive index on the light output. A moderate optical gain of 10% is obtained as the refractive index of the encapsulant material increases from 1.42 to 1.64, which is explained with the simulations as a strong effect of the die parameters (roughness and back mirror) on the light extraction.