Plasmon-enhanced Luminescence Research Articles

Soft scaffold aided plasmon-enhanced upconversion luminescence and its application in vascular endothelial growth factor (VEGF) detection

The dimensioning of glutathione-coated gold nanoparticles (GSH-Au NPs) greatly enhanced the luminescence intensity of upconversion nanoparticles (UCNPs) in close proximity and offered significant implications for biomedicine and materials science. According to systematic studies, the luminescence changes between UCNPs and AuNPs are enhanced by a well-tuned electric field-induced absorption, especially when the distance between the two is approximately 5 nm. At this distance, an upconversion enhancement factor of approximately 4.4 is achieved at a wavelength of 361 nm. This maximized plasmonic enhancement effect was subsequently employed for the quantification of Vascular Endothelial Growth Factor (VEGF) with the well-fabricated plasmon-enhanced luminescence complex (PELC) by replacing the ssDNA with the corresponding aptamer. This complex provides a basis for the rational design of a hybrid metal-upconversion complex to enhance luminescence for bioimaging and sensing applications.

Feasibility of Integrating Bimetallic Au-Ag Non-Alloys Nanoparticles Embedded in Reduced Graphene Oxide Photodetector

To coordinate the resonant wavelength of the plasmonic nanoparticles (NPs), the emission band of the reduced graphene oxide (rGO) photodetector at the NIR-region is crucial for the optimal plasmon-enhanced luminescence in the device. In contrast to monometallic NPs, where limits the dimensions and extended resonant wavelength, we integrated an Au-Ag bimetallic NPs (BMNPs) to enable resonance tuning at the longer wavelength at the excitation source of 785 nm. These features showed an increase in radiative recombination rates as well as the quantum yield efficiency of the device. The BMNPs were produced from the dewetting process of 600 °C and 500 °C, both at 1 min after the deposition thickness layer of Au (8 nm) and Ag (10 nm) on the Si substrate using the electron-beam evaporation process. Our BMNPs-rGO photodetector exhibited the responsivity of 2.25 · A W−1, Jones of specific detectivity of 2.45×1011Jones, and external quantum efficiency (EQE) of 356%. The rise time and fall time for the photodetector were 32 ns and 186 ns, respectively. This work provided an essential information to enable the versatile plasmon-enhanced application in 2-dimensional (2D) material optoelectronic devices.

Plasmon-enhanced luminescence of rare-earth ions by gold and silver nanoparticles in PMMA

In this work plasmon resonances in gold and silver nanoparticles to enhance luminescent properties of PMMA doped with different rare-earth ions densities are investigated. For this purpose, a rate equation model based on the Förster theory is used. This model describes the luminescent dynamics between donor and acceptor rare earth ions and considers the electric field changes due to metallic nanoparticles. The MNPBEM Matlab toolbox is used to calculate the electric field in our system, including the electric field of the excitation and the electric field induced by the nanoparticle. The results show that rare earth luminescence can be increased in the proximity of spherical gold and silver nanoparticles due to the change in the optical field and the transition rates. Accordingly, the rate equation model proposed here explains the increase in luminescent emission when the dopants interact with the metal nanoparticles. Additionally, the calculations allow to find the optimal conditions of nanoparticle size and excitation wavelength to achieve the maximum amplification of optical field and, therefore, the maximum amplification of the emission of rare earth ions.

Plasmonic Properties of Individual Gallium Nanoparticles.

Gallium is a plasmonic material offering ultraviolet to near-infrared tunability, facile and scalable preparation, and good stability of nanoparticles. In this work, we experimentally demonstrate the link between the shape and size of individual gallium nanoparticles and their optical properties. To this end, we utilize scanning transmission electron microscopy combined with electron energy loss spectroscopy. Lens-shaped gallium nanoparticles with a diameter between 10 and 200 nm were grown directly on a silicon nitride membrane using an effusion cell developed in house that was operated under ultra-high-vacuum conditions. We have experimentally proven that they support localized surface plasmon resonances and their dipole mode can be tuned through their size from the ultraviolet to near-infrared spectral region. The measurements are supported by numerical simulations using realistic particle shapes and sizes. Our results pave the way for future applications of gallium nanoparticles such as hyperspectral absorption of sunlight in energy harvesting or plasmon-enhanced luminescence of ultraviolet emitters.

Improving the UV-light stability of silicon heterojunction solar cells through plasmon-enhanced luminescence downshifting of YVO4:Eu3+,Bi3+ nanophosphors decorated with Ag nanoparticles

The ultraviolet (UV) light stability of silicon heterojunction (SHJ) solar cells should be addressed before large-scale production and applications. Introducing downshifting (DS) nanophosphors on top of solar cells that can convert UV light to visible light may reduce UV-induced degradation (UVID) without sacrificing the power conversion efficiency (PCE). Herein, a novel composite DS nanomaterial composed of YVO4:Eu3+,Bi3+ nanoparticles (NPs) and Ag NPs was synthesized and introduced onto the incident light side of industrial SHJ solar cells to achieve UV shielding. The YVO4:Eu3+,Bi3+ NPs and Ag NPs were synthesized via a sol–gel method and a wet chemical reduction method, respectively. Then, a composite structure of the YVO4:Eu3+,Bi3+ NPs decorated with Ag NPs was synthesized by an ultrasonic method. The emission intensities of the YVO4:Eu3+,Bi3+ nanophosphors were significantly enhanced upon decoration with an appropriate amount of ∼20 nm Ag NPs due to the localized surface plasmon resonance (LSPR) effect. Upon the introduction of LSPR-enhanced downshifting, the SHJ solar cells exhibited an ∼0.54% relative decrease in PCE degradation under UV irradiation with a cumulative dose of 45 kW h compared to their counterparts, suggesting excellent potential for application in UV-light stability enhancement of solar cells or modules.

Towards Electrochemiluminescence Microscopy Exploration of Plasmonic-Mediated Phenomena at the Single-Nanoparticle Level.

The rational design of functional plasmonic metasurfaces and metamaterials requires the development of high-throughput characterization techniques compatible with operando conditions and capable of addressing single-nanostructures. In their work, Wei et al. demonstrate the use of electrochemiluminescence microscopy to investigate the mechanism behind plasmon-enhanced luminescence induced by gold nanostructures. The use of gold plasmonic arrays was exploited to achieve the rapid spectroscopic evaluation of all the individual nanostructures, and the correlation of the results with high- resolution electron microscopy analysis, guaranteeing a strict one-to-one correspondence. The authors were able to identify two different mechanisms for the enhancement of [Ru(bpy)3 ]2+ -tri-n-propylamine electrochemiluminescence mediated by single gold nanoparticles and by small plasmonic clusters. In the future, the proposed characterization could be used for the rapid and in situ spectroscopic analysis of more complex plasmonic nanostructures and metasurfaces.

Plasmon-Enhanced Ultraviolet Luminescence in Colloid Solutions and Nanostructures Based on Aluminum and ZnO Nanoparticles.

Aluminum nanoparticles attract scientific interest as a promising low-cost material with strong plasmon resonance in the ultraviolet region, which can be used in various fields of photonics. In this paper, for the first time, ultraviolet luminescence of zinc oxide nanoparticles in colloid solutions and nanostructure films in the presence of plasmonic aluminum nanoparticles 60 nm in size with a metal core and an aluminum oxide shell were studied. Mixture colloids of ZnO and Al nanoparticles in isopropyl alcohol solution with concentrations from 0.022 to 0.44 g/L and 0.057 to 0.00285 g/L, correspondingly, were investigated. The enhancement of up to 300% of ZnO emission at 377 nm in colloids mixtures with metal nanoparticles due to formation of Al-ZnO complex agglomerates was achieved. Plasmon nanostructures with different configurations of layers, such as Al on the surface of ZnO, ZnO on Al, sandwich-like structure and samples prepared from a colloidal mixture of ZnO and Al nanoparticles, were fabricated by microplotter printing. We demonstrated that photoluminescence can be boosted 2.4-fold in nanostructures prepared from a colloidal mixture of ZnO and Al nanoparticles, whereas the sandwich-like structure gave only 1.1 times the amplification of luminescence. Calculated theoretical models of photoluminescence enhancement of ideal and weak emitters near aluminum nanoparticles of different sizes showed comparable results with the obtained experimental data.

Engineering Plasmon-Enhanced Fluorescent Gold Nanoclusters Using Bovine Serum Albumin as a Novel Separation Layer for Improved Selectivity.

The combination of gold nanoclusters (AuNCs) with surface plasmonic metal nanomaterials is an effective and direct method to improve the photoluminescence efficiency of AuNCs. However, the plasmon-enhanced AuNC luminescence strategies usually utilize silica as the separation layer, which requires further functionalization because the silica layer has no functional groups for in situ bonding of AuNCs. Therefore, it appears as a crucial need to develop an appropriate separation layer for the preparation of plasmon-enhanced AuNC luminescent nanomaterials. In this work, employing bovine serum albumin (BSA) as a novel separation layer, we prepared gold nanoparticles (AuNPs)@BSA@Au35NCs by a controllable and in situ synthesis method. BSA can form a BSA layer on the surface of AuNPs through Au-S bonds. Meanwhile, BSA can reduce AuCl4- ions to generate Au35NCs. In comparison with pure BSA-AuNCs, the quantum yield of the AuNPs@BSA@Au35NCs was increased by nearly 7 times as a result of plasmonic coupling, and the time of in situ synthesis of Au35NCs was shortened by 8 h. More importantly, the preparation of the BSA layer was simple and time-saving without functionalization, in contrast to the previously reported silica layer. Moreover, the simulation calculation of different dimensions determined the optimal binding sites between Au35NCs and BSA, confirming that BSA can be an effective spatial spacer. Finally, it was found that the BSA layer between AuNPs and AuNCs can improve the specificity of AuNCs toward H2S, which is extremely difficult for pure BSA@AuNCs.

Shell-Isolated Assembly of Atomically Precise Nanoclusters on Gold Nanorods for Integrated Plasmonic-Luminescent Nanocomposites.

In this work, we integrate atomically precise noble metal nanoclusters (NCs) on gold nanorods (AuNRs) to create hybrid plasmonic-luminescent nanomaterials. Initially, we assemble luminescent Ag29(LA)12 NC (LA = lipoic acid) to silica shell-encapsulated AuNRs. The resulting nanostructure shows plasmon-enhanced luminescence in aqueous medium as well as in the solid state. Atomic precision of the fluorophores used in this case allows detailed characterization of individual nanocomposites by diverse techniques, including transmission electron microscopy (TEM) and 3D electron tomographic reconstruction. We extend this strategy to prepare similar structures with gold NC protected with bovine serum albumin (Au30BSA). These two examples demonstrate the generic nature of the present strategy in preparing plasmonic-luminescent hybrid nanostructures using atomically precise NCs.

Plasmon-Enhanced Electrochemiluminescence of PTP-Decorated Eu MOF-Based Pt-Tipped Au Bimetallic Nanorods for the Lincomycin Assay.

Plasmonic bimetal nanostructures can be employed to amplify electrochemiluminescence (ECL) signals. In this work, a high-performance ECL platform was constructed using a europium metal-organic framework (MOF) as a luminophore and Au-Pt bimetallic nanorods (NRs) as a plasma source. Due to the SPR effect of Au-Pt NRs, the aptasensor exhibits 2.6-fold ECL intensity compared to that of pure polyaniline (PANI)-decorated perylene tetracarboxylic dianhydride (PTCA)/Eu MOF. Moreover, decoration with PTP greatly enhances the conductivity and stability of Eu MOF, resulting in sizeable plasmon-enhanced electrochemical luminescence. The as-designed plasmon-enhanced ECL aptasensor displayed highly sensitive detection for lincomycin (Lin). The as-proposed aptasensor could quantify Lin from 0.1 mg/mL to 0.1 ng/mL with a limit of detection (LOD) of 0.026 ng/mL.

The role of gold nanoparticles' aspect ratio in plasmon-enhanced luminescence and the singlet oxygen generation rate of Mo6 clusters.

Here we present a study on the effect of the aspect ratio (AR) of gold nanoparticles on the emission intensity and singlet oxygen production rate of hexamolybdenum cluster-doped silica particles. It was shown that these parameters can be enhanced gradually up to 6.7- and 13-fold with the AR.

Structures, plasmon-enhanced luminescence, and applications of heterostructure phosphors.

Heterostructure phosphor composites have been used widely in the fields of targeted bio-probes and bio-imaging, hyperthermia treatment, photocatalysis, solar cells, and fingerprint identification. The structures, plasmon-enhanced luminescence and mechanism of metal/fluorophore heterostructure composites, such as core-shell nanocrystals, multilayers, adhesion, islands, arrays, and composite optical glass, are reviewed in detail. Their extended applications were explored widely since the surface plasmon resonance effect increased the up-conversion efficiency of fluorophores significantly. We summarize their synthesis methods, size and shape control, absorption and excitation spectra, plasmon-enhanced up-conversion luminescence, and specific applications. The most important results acquired in each case are summarized, and the main challenges that need to be overcome are discussed.

Feasibility of using bimetallic Au-Ag nanoparticles for organic light-emitting devices.

Matching the resonant wavelength of plasmonic nanoparticles (NPs) and the emission band of organic materials is critical for achieving optimal plasmon-enhanced luminescence in organic light-emitting devices (OLEDs). However, the spectral matching is often unsatisfactory because the interior architecture of OLEDs limits the dimensions of the NPs to support the desired wavelength adjustment. In this article, we proposed a design strategy via AuxAg1-x alloy NPs to enable resonance tuning while preserving the size of the NP to suit the OLED design requirements. The bimetallic NPs, especially for x < 0.6, not only add one more degree of freedom to vary the plasmon wavelength but also provide the benefits of higher scattering and more intense and outspread electric fields over a broader spectrum compared to Au monometallic NPs. These features allow smaller NPs, which are more compatible with OLED interiors, to scatter electric fields more efficiently and increase the density of molecules interacting with the NP plasmons. In the presence of a nearby dipole emitter, the bimetallic NPs can simultaneously increase radiative enhancement and suppress non-radiative losses, which are advantageous for increasing the quantum yield and luminescence efficiency of the emitter. These improvements are associated with lower intraband and interband activities resulting from the higher molar fraction of Ag in the alloy NPs. We provided composition mappings to achieve enhanced luminescence for specified wavelengths at fixed NP sizes. Finally, we theoretically demonstrated that the bimetallic NPs could improve the light-extraction efficiency of OLEDs better than Au monometallic NPs. This work provides essential guidance to enable versatile plasmon-enhanced applications with predefined nanostructural geometries and wavelengths to match the device requirements.

Enhanced optical cross-section of radiation induced defect centers under plasmon resonance conditions: Shifting stimulation wavelength of optically stimulated luminescence dosimeters

Plasmon-enhanced luminescence is an important tool for development of advanced sensing technologies but the mechanisms originating these enhancements are still in debate. In this work, we investigate plasmon-enhanced luminescence mechanisms using the Optically Stimulated Luminescence (OSL) from defect centers in X-ray irradiated sodium chloride nanocrystals deposited on silver nanoparticle (AgNP) films with varying plasmon properties upon blue, green, and red OSL stimulation. Although the absolute OSL intensity for NaCl crystals is higher upon blue stimulation, under plasmon resonance conditions, higher absolute OSL intensity occurs upon green stimulation and the largest OSL enhancements are observed by employing red stimulation. These results suggest that, as long as the OSL stimulation wavelength is well tuned with the film plasmon band, plasmonic coupling does not depend on the trap depth and that the largest luminescence enhancements are achieved in spectral regions where the optical cross-sections of the defect centers are smaller. In terms of radiation dosimetry applications, this result allows to shift the stimulation wavelength farther from the OSL emission window, improving the signal to noise ratio and the dose assessment sensitivity and accuracy.

Gold nanorods modified Eu: Y2O3 dispersed PVA film as a highly sensitive plasmon-enhanced luminescence probe for excellent and fast non-enzymatic detection of H2O2 and glucose

This article addresses a high sensitivity, non-invasive, and use-throw in nature type biocompatible Eu: Y2O3 dispersed PVA film with gold nanorod (AEYCP film) fluorescent sensing probe for non-enzymatic detection of hydrogen peroxide (H2O2) and glucose (C6H12O6). The fluorescence spectra of the as-synthesized AEYCP fluorescent film consist of some sharp emission (most intense peak at ∼611 nm, owing to the 5D0-7F2 transition) which corresponds to electrical and magnetic dipole transitions. In the presence of H2O2 and glucose, the fluorescence intensity of the AEYCP film gets quenched due to the reduction of electron-hole pair, at the Eu center. The AEYCP film shows excellent fluorescence quenching in the presence of H2O2 at ∼500 nM (with a low detection limit of 1.80 × 10−9 M) and glucose (with a low detection limit 1.60 × 10-6 M).Herein, we envision that our result provides an insight for the synthesis of rare earth metal-doped oxide flexible,non-enzyme mimicking fluorescent probe for different biomedical applications.

Microwave-Assisted Growth of Silver Nanoparticle Films with Tunable Plasmon Properties and Asymmetrical Particle Geometry for Applications as Radiation Sensors

We report a simple and fast microwave-assisted method to grow silver nanoparticle films with tunable plasmon resonance band. Microwaving time controls nucleation and growth as well as particle agglomeration, cluster formation, particle morphology, and the plasmonic properties. Films produced with times shorter than 30 s presented a single well-defined plasmon resonance band (~ 400 nm), whereas films produced with times longer than 40 s presented higher wavelength resonances modes (> 500 nm). Plasmon band position and intensity can be easily tuned by controlling microwaving time and power. SEM and AFM images suggested the growth of asymmetrical silver nanoparticles. Simulated extinction spectra considering particles as spheres, hemispheres, and spherical caps were performed. The films were employed to enhance the sensitivity of ionizing radiation detectors assessed by optically stimulated luminescence (OSL) via plasmon-enhanced luminescence. By tuning the plasmon resonance band to overlap with the OSL stimulation (530 nm), luminescence enhancements of greater than 100-fold were obtained, demonstrating the importance of tuning the plasmon resonance band to maximize the OSL intensity and detector sensitivity. This versatile method to produce silver nanoparticle films with tunable plasmonic properties is a promising platform for developing small-sized radiation detectors and advanced sensing technologies.

Facile synthesis and enhanced luminescence properties of MoO3−x/YF3:Eu3+ composites

At present, the main bottleneck that restricts the application of rare earth luminescent materials is the lower luminescence intensity of materials. Based on the unique local surface plasmon resonance (LSPR) of MoO3 − x, we developed new MoO3 − x / YF3 : Eu3 + composites with strong luminescence. The composites possessed stronger luminescent intensity than individually dispersed YF3 : Eu3 + , exhibiting the MoO3 − x / YF3 : Eu3 + composites, which could be used as highly efficient imaging materials. It is proposed that the ultraviolet-excited LSPR of MoO3 − x is the primary reason for the enhanced luminescence of YF3 : Eu3 + . Meanwhile, the plasmon-enhanced luminescence can be partly absorbed by the MoO3 − x particles to re-excite its higher energy electrons, thus leading to the selective boost luminescence intensity of MoO3 − x / YF3 : Eu3 + composites. We give insight on the development of plasmon-sensitized luminescence materials.

Building vertical gold nanorod arrays to enhance upconversion luminescence of &lt;i&gt;β&lt;/i&gt;-NaYF&lt;sub&gt;4&lt;/sub&gt;: Yb&lt;sup&gt;3+&lt;/sup&gt;/Er&lt;sup&gt;3+&lt;/sup&gt; nanocrystals

The plasmon resonance effect is one of the effective ways to enhance the upconversion (UC) luminescence, which is realized by enhancing the electromagnetic field from incident light interacting with free electrons of AuNRs surface. In this work, a series of GVA@SiO&lt;sub&gt;2&lt;/sub&gt;@NaYF&lt;sub&gt;4&lt;/sub&gt;:Yb&lt;sup&gt;3+&lt;/sup&gt;/Er&lt;sup&gt;3+&lt;/sup&gt; composite structures with different thickness values of SiO&lt;sub&gt;2&lt;/sub&gt; isolation layer is successfully built from self-assembled gold nanorods, steamed SiO&lt;sub&gt;2&lt;/sub&gt;, and spin-coating rare-earth nanocrystals. The results of the SEM indicate that the size of gold-nanorods is approximately 22 nm in diameter and 65 nm in length. The X-ray diffraction and transmission electron microscope results demonstrate that the NaYF&lt;sub&gt;4&lt;/sub&gt;:Yb&lt;sup&gt;3+&lt;/sup&gt;/Er&lt;sup&gt;3+&lt;/sup&gt; nanocrystals possess hexagonal-phase structure with a size of about 20 nm. Under 980 nm near-infrared (NIR) excitation, the UC emission characteristics of GVA@SiO&lt;sub&gt;2&lt;/sub&gt;@NaYF&lt;sub&gt;4&lt;/sub&gt;:Yb&lt;sup&gt;3+&lt;/sup&gt;/Er&lt;sup&gt;3+&lt;/sup&gt; composite structure are studied by using a confocal microscope spectroscopic test system, and regulated by changing the thickness of SiO&lt;sub&gt;2&lt;/sub&gt; isolation layer. The results indicate that the UC emission intensity of NaYF&lt;sub&gt;4&lt;/sub&gt;:20%Yb&lt;sup&gt;3+&lt;/sup&gt;/2%Er&lt;sup&gt;3+&lt;/sup&gt; nanocrystals is enhanced by about 8.8 times, and the enhancement factor of red UC emission intensity is about 16.2. In order to further prove the enhancement effect of the red UC emission, the GVA@SiO&lt;sub&gt;2&lt;/sub&gt;@NaYF&lt;sub&gt;4&lt;/sub&gt;:40%Yb&lt;sup&gt;3+&lt;/sup&gt;/20%Er&lt;sup&gt;3+ &lt;/sup&gt;composite structure with red UC emission is constructed in the same way. It can be found that the UC emission intensity of NaYF&lt;sub&gt;4&lt;/sub&gt;:40%Yb&lt;sup&gt;3+&lt;/sup&gt;/20%Er&lt;sup&gt;3+&lt;/sup&gt; nanocrystals is enhanced by 8.7 times and the red UC emission intensity is raised by about 9.7 times under the 980 nm NIR excitation. The corresponding excitation enhancement mechanism is simulated according to the power excitation dependence. And it is found that the rate of UC emission decreases and the R/G ratio also decreases with the excitation pump power increasing. The analysis of the above results shows that the excitation enhancement plays a leading role and is accompanied by emission enhancement. Meanwhile, the study of Er&lt;sup&gt;3+&lt;/sup&gt; ion dynamic process indicates that the Er&lt;sup&gt;3+&lt;/sup&gt; ion transition rate is accelerated due to the coupling from UC emission peaks and gold nanorod absorption peaks in GVA@SiO&lt;sub&gt;2&lt;/sub&gt;@NaYF&lt;sub&gt;4&lt;/sub&gt;:40%Yb&lt;sup&gt;3+&lt;/sup&gt;/20%Er&lt;sup&gt;3+ &lt;/sup&gt;composite structure. The enhancement mechanism of UC emission is also simulated, which further proves that the excitation enhancement is dominant. This kind of composite structure can not only help us to further understand the physics mechanism of the plasmon-enhanced UC luminescence but also promote the applications of rare-earth materials in medical imaging and fingerprint recognition.

Enhanced luminescence properties of Eu3+-doped high silica glass by Ag nanoparticles

Eu3+ and Ag nanoparticles (Ag-NPs) doped high silica glass (HSG) was synthesized by absorbing and sintering porous glass. The effect of localized surface plasmon resonance (LSPR) of Ag-NPs on absorbance, luminescence properties and decay curves was investigated. The results indicate that Ag-NPs are effectively doped into HSG. The surface plasmon coupling can be formed between the Eu3+ ions and the Ag-NPs surface because the broad absorption band of Ag-NPs overlaps with the excitation peaks of Eu3+. The profiles of the excitation and emission spectra were not affected by Ag-NPs. By optimizing the Ag concentration, the emission intensity and quantum yield (QY) of HSG-Eu3+-0.1%Ag are significantly higher than those of HSG-Eu3+. Plasmon-enhanced luminescence can occur through enhancement of local electromagnetic field and radiative decay rate.

Surface plasmon-enhanced luminescence of NaYFPO4:Dy3+ phosphor by Ag nanoparticles

Ag nanoparticles (Ag-NPs) were adsorbed onto the surface of phosphor NaYFPO4:Dy3+ through an in situ reduction. The structure, morphology, composition, and optical properties were confirmed by X-ray diffraction, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, and photoluminescence spectroscopy, respectively. The excitation peaks slightly shifted to long waves in the presence of Ag-NPs. Emission intensity increased by 115% owing to the enhancement of the local electromagnetic field near Ag-NPs because of the localized surface plasmon resonance. All these results indicated that the sample was a promising candidate for white LED devices.