External Quantum Yield Research Articles

Ni2+ in Distorted Octahedral Geometry toward High-Efficiency NIR-II/III emitter.

Ni2+ activated phosphor has attracted wide attention because it can be radiated in near-infrared (NIR) II-III region; however, the low external quantum yield (EQY) hinders its further application (most are below 8%). In this work, distortion of crystallographic site strategy is proposed to enhance EQY. LaTiTaO6: 0.004Ni2+ exhibits an NIR emitting spectrum centered at 1450 nm with an EQY of ~ 9.00%, which has been the highest EQY of reported Ni2+ single-doped phosphor. Distortion degrees of the octahedral geometry in LaTiTaO6 and LaTiTaO6: 0.004Ni2+ changing from 0.038 to 0.047 result in the absorption efficiency of 38.6% due to the breaking of parity forbidden of the d-d transition, further improving the EQY. Besides, LaTiTaO6: 0.004Ni2+ mixed with LaTiTaO6: 0.04Cr3+ phosphors have demonstrated their application for spectral analysis. This work provides a new idea for constructing efficient NIR-II to NIR-III phosphors.

Metal Single Atom-Hydroxyl Incorporation in Poly(heptazine imide) to Create Active Sites for Photocatalytic Water Oxidation.

Poly(heptazine imide) (PHI) salts are extensively researched crystalline carbon nitride photocatalysts, but their photocatalytic water oxidation (PWO) performance is scarcely researched because of the difficulty in creating efficient active sites. Interference of metal ion (e.g., Na+ and K+) loss from the PHI salts in their PWO research has hardly been considered. Herein, metal single atom─OH (e.g., Co─OH) groups are incorporated into PHI to create efficient PWO active sites, via simple ion metathesis, hydrolysis, and deprotonation. The Co─OH modified PHI exhibits 9.3-fold higher PWO (oxygen evolution) activity than PHI, with an external quantum yield reaching 0.44% even at 600 nm. Excluding interference of the metal ion loss, the function of the Co─OH incorporation is evidenced mainly to facilitate the oxygen evolution reaction, as well as to promote photogenerated charge separation and raise visible light absorption, with the role of the OH especially revealed. Moreover, it is discovered that Na+ loss from sodium PHI will decrease its PWO activity, protonation of PHI has a detrimental effect on its PWO performance, and some other metal single atom─OH incorporation in PHI can also enhance its PWO activity. Overall, this work provides a general way to create PWO active sites in PHI.

(Invited) Silicon Nanocrystals and Electrum Nanoclusters with High Quantum Yield for Light Converting Applications

While QDs are typically made of semiconductors, metals at low dimensions also turn to discrete electronic structure. The characteristic transition size from bulk to nanodot is lower, because Fermi level position is at the band middle, while discretization of levels starts from the band edge. Therefore, only for sizes of a metal entity ~ 1 nm a QD-like behavior manifests.Here we show that metal nanoclusters Au16Ag7 of an electrum alloy (gold-silver) with adamantanethiolate ligands possess PL quantum yield of ~ 70% in a thiol-ene polymer matrix [1]. PL is in NIR range with a large Stokes shift. Due to parity-forbidden transition the PL lifetime is in microseconds. These characteristics are similar to silicon QDs, where optical transition is also partly forbidden. Luminescence from Si QDs (5-10 nm size) may also feature high quantum efficiency when a defect-free core with good surface passivation is prepared. We have demonstrated a new synthesis method, which can reduce precursor cost by an order of magnitude from the established HSQ-based technique [2]. Si QDs prepared in this way have near-unity internal and > 50% external (quantum yield) efficiency with a large Stokes shift. In both nanomaterials the re-absorption is suppressed, which is of value for several applications.One such application is a semi-transparent photovoltaics for glazing in building-integration. It is based on a luminescent solar concentrator concept, where high efficiency and a large Stokes shift are necessary requirements for nanophosphors. In this configuration absorbed solar light is re-emitted and a large fraction of it is guided by total internal reflection to the edges for collection by standard solar cells. As a proof-of-concept we fabricated 20x20 cm2 prototypes, where Si QD-doped polymer layer is sandwiched between glass plates in a triplex geometry. Such “solar windows” feature high transparency (>80%), low haze (<3%), high color rendering index (~ 88) and, at the same time, deliver up to 0.6 W of electrical peak power under one sun [3]. Original measurement techniques were developed to characterize large-area devices [4,5].

Tailoring emission characteristics of Na+-Sc3+ co-substituted CaMgGe2O6:Cr3+ phosphors for iris acquisition

The growing interest in Cr3+-doped broadband infrared phosphors stems from their promising applications in various fields. However, achieving highly efficient broadband emission based on these materials remains a significant challenge. To address this issue, we proposed a cation co-substitution method to enhance the near-infrared (NIR) emission of Cr3+-doped phosphors while simultaneously broadening the full width at half maximum (FWHM) of their emission peaks, as demonstrated in the case of CaMgGe2O6:Cr3+. Through controlled co-substitution of Ca2+ and Mg2+ cations by Na+ and Sc3+ cations, we prepared (Ca, Mg)1-x(Na, Sc)xGe2O6:Cr3+ (CMSxG:Cr3+) using a solid reaction method. This approach aims to deliberately adjust the strength of the crystal field experienced by Cr3+ to regulate the luminescence performance of the corresponding phosphors. Indeed, we observed a red shift of the emission peak from 850 to 902 nm, with the FWHM extending from 163 to 198 nm, as the concentration of ‘Na+-Sc3+’ pair increased, which would benefit iris acquisition. Importantly, the external quantum yield did not deteriorate; instead, it was enhanced from 13.6 to 26.2 %. Finally, we fabricated a broadband near infrared phosphor converted light-emitting diodes (pc-LED) by integrating CMSxG:Cr3+ phosphors with commercial 460 nm LEDs. An infrared output power of 118.01 mW at 300.00 mA was achieved with pc-LED based on Ca0.9Mg0.88(NaSc)0.1Ge2O6:0.02Cr3+ phosphor. Clear iris images acquired using these pc-LED as lighting sources demonstrate their potential applications in iris acquisition for biometrics.

Electrodeposition of Photosensitive Layers Based on Conducting Polymers and Zinc Phthalocyaninate, Their Structure and Photoelectrical Properties

Photosensitive hybrid layers were obtained by electrochemical polymerization of pyrrole and 3,4-ethylenedioxythiophene (EDOT) in the presence of water-soluble sodium salt of zinc octa(3ʹ,5ʹ-dicarboxyphenoxy)phthalocyaninate (ZnPc) containing 16 ionogenic carboxylate groups. It was found that the process of electrodeposition of hybrid layers most effectively occurs in galvanostatic and potentiostatic modes on the sublayer of the PEDOT-polyacid complex. The electronic and chemical structure and morphology of hybrid layers of polypyrrole (PPy) obtained in the presence of ZnPc were studied. Possible reasons are considered that the measured values of photosensitivity and external quantum yield of charge carrier generation in PPy-ZnPc are several times higher than in PEDOT-ZnPc.

Metal single atom-oxygen modification induced transformation of carbon nitride-based heterojunctions from type-II to S-scheme for efficient photocatalytic overall water splitting

Constructing semiconductor S-scheme hetero-(homo-)junctions (SSHs) is one of the most effective ways to enhance the photocatalytic overall water splitting (POWS) performance, but encumbered by deficiency of efficient water-oxidizing semiconductors. Herein, tungsten single atom-oxygen group (W-O) modified polymeric carbon nitride (WPCN, an example of metal single atom-oxygen group modified PCN) was used as a water-oxidizing semiconductor to construct a CdS/WPCN SSH, for which the W-O modification plays a key role that causes transformation from a PCN/CdS type-II heterojunction to the CdS/WPCN SSH which exhibits remarkably enhanced photoexcited charge separation than single CdS and WPCN. Pt-CdS/WPCN exhibits 2.6 and 7.2 times higher POWS activity than Pt-WPCN and Pt-CdS, respectively, further demonstrating the key role of the SSH, and lower activity than Pt@Cr2O3-CdS/WPCN that exhibits 5.4-fold higher activity than Pt@Cr2O3-PCN/CdS, and especially, higher photochemical stability by suppressing rapid photocorrosion of CdS. The solar-to-hydrogen conversion efficiency of Pt@Cr2O3-CdS/ WPCN reaches 0.014 %, with an external quantum yield of 0.093 % at 420 nm. This work reveals the role of metal single atom-oxygen modification of PCN in SSHs and provides a way to suppress rapid photocorrosion of CdS.

Moisture‐Resistant Orange Emitters with Near‐Unity Quantum Yield from Mn2+ Alloyed Vacancy‐Ordered Quadruple Perovskites

AbstractMn2+‐doped metal halide perovskites present remarkable optical properties in optoelectronic applications, although the realization of high efficiency and stability is still a challenge. In this work, a series of highly efficient and stable orange‐emitting Mn2+ alloyed Cs4Cd1‐xMnxBi2Cl12 single crystals are successfully synthesized via a hydrothermal reaction. Combined with the crystal structure and spectral characterization at 7 K, the site occupation of Mn2+ and defect emission are systematically discussed. Benefiting from the effective [BiCl6]3−→[MnCl6]4− energy transfer and lattice distortion, these single crystals exhibit a maximum internal and external quantum yield of ≈97% and ≈65% at 35% heavy doping level. Interestingly, these Mn2+‐alloyed single crystals exhibit remarkably waterproof stability, no decrease in emission intensity is observed after immersion in deionized water for 4 h. After soaking in deionized water for 100 days, the internal quantum yield can still maintain 44%, implying good chemical stability and moisture resistance due to the formation of protective BiOCl layer. This work provides new insights into the optimization mechanism for Mn2+ luminescence and overcoming the downside of their waterproofing in humid conditions.

Why do Si quantum dots with stronger fast emission have lower external photoluminescence quantum yield?

We explain the observed correlation of increased fast emission of quantum dots with lower photoluminescence quantum yield as selective lifetime-based quenching, or in other words, preferential switching off of quantum dots with slow emission.

Investigating Solid-State Luminescent Properties of New Cadmium(II) and Lead(II) Oxamato-Based Coordination Polymers

Two novel coordination polymers were synthesized through the reaction of the Hpcpa2− ligand (H3pcpa = N-(4-carboxyphenyl)oxamic acid) with cadmium(II) and lead(II) metal ions, yielding [Cd2(Hpcpa)2(H2O)6]n⋅H2O (1) and [Pb(Hpcpa)(H2O)]n (2). Structural analysis by single-crystal X-ray diffraction revealed that 1 consists of one-dimensional zigzag polymeric chains, while 2 is a three-dimensional polymer network. Additionally, investigations of their optical properties were carried out in a comparative study involving the previously reported pcpa-based coordination polymers {[Zn(Hpcpa)(H2O)3]·0.5H2O}n and {[Gd2(Hpcpa)3(H2O)5]·H2O}n], called here as 3 and 4, respectively. Under 330 nm excitation wavelength, all compounds exhibited broad emission bands spanning from 350 to 650 nm. Particularly, 1 and 3 displayed notable external quantum yields of 15.4 and 12.8%, respectively, highlighting their potential in luminescent applications.

High external quantum yield in near-infrared phosphor Bi2Ga4O9:Cr3+ excited by near-ultraviolet or blue light

The proliferation of portable and intelligent devices featuring Near-Infrared (NIR) light sources as a central component has resulted in a significant need for compact NIR light sources. The technique of NIR phosphor-converted light-emitting diodes (NIR-pc-LEDs) could offer a fresh viewpoint on NIR light sources. The performance of NIR-pc-LEDs is directly influenced by NIR phosphors. However, the development of NIR phosphors with high external quantum yield (EQY) NIR phosphors has been hampered. In this work, we report a mullite-structure NIR phosphor, Bi2Ga4O9: Cr3+ (BGO), which exhibits excellent NIR luminescence properties. The emission spectrum of the optimal doped sample BGO:0.06Cr3+ has two emission peaks at 711 and 763 nm. All samples can be efficiently excited by commercial 365 nm near-ultraviolet LED chips and 450 nm blue LED chips. The internal quantum yield (IQY) reaches an astonishing value of 89.13 % and an EQY of about 65.36 % at 365 nm excitation. Furthermore, BGO:0.06Cr3+ shows a high IQY (∼87.78 %) and EQY (∼41.64 %) upon 450 nm excitation. Moreover, concerning thermal stability, the integrated photoluminescence intensity remains at 82 % and 42 % of that at room temperature when measured at 373 K and 423 K, respectively. The capsuled NIR-pc-LED device can be utilized for blood veins imaging, food safety analysis, and information encryption. These results highlight the promising commercial prospects of BGO:0.06Cr3+ in the fields of bio-imaging and non-destructive testing, among others.

From Ancient Blue Pigment to Unconventional NIR Phosphor: A Thermal-Stable Near-Infrared I/II Broadband Emission from Ca1-xSrxCuSi4O10 Solid Solution.

Phosphors used in NIR spectroscopy require broadband emission, high external quantum yield, good ability, as well as a tunable spectral range to meet the detection criteria. Two-dimensional copper silicates MCuSi4O10 (M = Ca, Sr, Ba) play an important part in ancient art and technology as synthetic blue pigments. In the recent years, these compounds were reported to show a broad near-infrared emission when excited in the visible region. Inspired by the tunable structure of MCuSi4O10, a series of broadband phosphors Ca1-xSrxCuSi4O10 were designed for realizing continuously tunable NIR emission by a modulated Cu2+ crystal field environment. The emission maximum exhibits a red shift from 915 to 950 nm and the integral intensity enhances as the Sr2+ content varies in the range of 0-0.50, which is led by the lattice expansion and the following weakened crystal field splitting on tetrahedral-coordinated Cu2+. Compared to CaCuSi4O10, the optimized sample Ca0.5Sr0.5CuSi4O10 shows enhanced NIR emission by about 2.0-fold. It exhibits quite a high external quantum efficiency covering the NIR-I and -II regions (λmax = 950 nm, fwhm = 135 nm, EQE = 26.3%) with a strong absorption efficiency (74.7%) and a long excited-state lifetime (134 μs). These solid-solution phosphors (x = 0.0-0.5) show excellent thermal stability and maintain over 50% of the RT intensity at 200 °C. The optimized phosphor was encapsulated with red-light chips to fabricate NIR pc-LED and put into night-vision application. These good properties make these Cu2+-activated NIR phosphors appealing for multiple applications such as nondestructive testing, night version, lasers, and luminescent solar concentrators.

Achieving Nearly Quantitative (∼100%) IQE and 42.3% EQE Across NIR‐I and NIR‐II Regions with Cr3+‐doped Cs2NaScCl6 under 300 nm Excitation

AbstractLead‐free rare‐earth‐based perovskites have received widespread attention for their unique optical properties, although achieving efficient broadband near‐infrared (NIR) emission with these materials remains a challenge. Here the synthesis of a rare earth‐based double perovskite (Cs2NaScCl6) by an improved solid phase method is reported. The doping of Cr3+ led to the formation of [CrCl6]3− octahedron, which exhibited a broadband NIR emission peaked at 950 nm and a half‐peak width of 162 nm. It is worth noting that with the same actual Cr3+ content, the luminous intensity of Cs2NaScCl6 synthesized by the improved solid‐phase synthesis is four times higher than the product synthesized by the hydrothermal method. an efficient Cl−‐Cr3+ charge transfer sensitization facilitated by localized electrons in [CrCl6]3− octahedron is the mechanism for the strong NIR emission of Cr3+ is proposed. Calculations based on density functional theory and Bader charge analysis support the notion that electrons in [CrCl6]3− octahedrons are strongly localized in Cs2NaScCl6:Cr3+, which is conducive to the Cl−–Cr3+ charge transfer process, resulting the internal quantum efficiency of 100% and external quantum yield as 42.3%. The highly efficient ultra‐broadband NIR emission with excellent stability offers many opportunities for applications in the field of NIR night vision and bio‐imaging.

Solution-Obtained (NH4)3In0.95Sb0.05Cl6 with High External Photoluminescence Quantum Yield and Excellent Antiquenching Properties.

The efficient broad-band emission from low-dimensional metal halides has garnered significant interest. However, most of these materials exhibit poor stability at the operating temperature of light-emitting diodes. In this study, using the solution method (temperature lower than 90 °C), a new compound (NH4)3In0.95Sb0.05Cl6 was obtained with the structure in the Pnma space group featuring unit-cell parameters of a = 12.3871(4) Å, b = 24.9895(9) Å, and c = 7.7844(3) Å. (NH4)3In0.95Sb0.05Cl6 can be prepared by doping (NH4)2InCl5·H2O when the Sb3+ feeding ratio is in the range of 30-80%. Thermal analysis reveals that (NH4)3In0.95Sb0.05Cl6 is stable up to 320 °C. (NH4)3In0.95Sb0.05Cl6 exhibits broad-band yellow-white emission with extremely high internal and external photoluminescence quantum yields of 93 and 77%, respectively. Interestingly, (NH4)3In0.95Sb0.05Cl6 displays remarkable resistance to thermal quenching, retaining 83% of its initial photoluminescence intensity at 80 °C. A white light-emitting diode is fabricated by combining (NH4)3In0.95Sb0.05Cl6 with a commercial phosphor, and a high color rendering of 92.8 was obtained. This work presents an environmentally friendly, efficient, stable UV-excited broad-band emission material for potential solid-state lighting applications.

Enhancing Up-Conversion Luminescence Using Dielectric Metasurfaces: Role of the Quality Factor of Resonance at a Pumping Wavelength.

Photonic applications of up-conversion luminescence (UCL) suffer from poor external quantum yield owing to a low absorption cross-section of UCL nanoparticles (UCNPs) doped with lanthanide ions. In this regard, plasmonic nanostructures have been proposed for enhancing UCL intensity through strong electromagnetic local-field enhancement; however, their intrinsic ohmic loss opens additional nonradiative decay channels. Herein, we demonstrate that dielectric metasurfaces can overcome this disadvantage. A periodic array of amorphous-silicon nanodisks serves as a metasurface on which a layer of UCNPs is self-assembled. Sharp resonances supported by the metasurface overlap the absorption wavelength (λ = 980 nm) of UCNPs to excite them, resulting in the enhancement of UCL intensity. We further sharpen the resonances through rapid thermal annealing (RTA) of the metasurface, crystallizing silicon to reduce intrinsic optical losses. By optimizing the RTA condition (at 1000 °C for 20 min in N2/H2 (3 vol %) atmosphere), the resonance quality factor improves from 17.2 to 32.9, accompanied by an increase in the enhancement factor of the UCL intensity from 86- to over 600-fold. Moreover, a reduction in the intrinsic optical losses mitigates the UCL thermal quenching under a high excitation density. These findings provide a strategy for increasing light-matter interactions in nanophotonic composite systems and promote UCNP applications.

The development of a new efficient red phosphor based on Eu2+ doped traditional inorganic oxygenate-perovskite compounds

The halide-perovskite type phosphors have been aroused extensive attention in recent years for their high quantum efficiency, but traditional oxygenate-perovskite type phosphors with Eu2+ activator have not been studied extensively so far. To fill this void, we dope Eu2+ into a typical perovskite host lattice SrZrO3 to produce an efficient phosphor SrZrO3:xEu2+. Theoretical calculation reveals that SrZrO3 has an indirect band gap of 3.776 eV. Phosphors SrZrO3:xEu2+ show bright red emission peaking at 605 nm under 450 nm blue light excitation with the full width at half maximum (FWHM) of 60 nm. The optimized concentration of Eu2+ is x = 0.10, and the quenching mechanism originates from the dipole-dipole interactions. The external quantum yield of optimal sample, SrZrO3:0.10Eu2+ can reach up to a high value of 50%. Temperature dependent luminescent properties studies show that the fluorescence integrated intensity of the sample at 425 K remains at 80% of that at 300 K. Finally, a white light-emitting diode (LED) is fabricated with color rendering index of 73 and color temperature of 3576 K. Thus, phosphor SrZrO3:0.10Eu2+ has great potential in fields of WLED lamp.

Cationic substitution engineering achieves higher efficiency and thermal stability of Cr3+-activated phosphor for pepper (Capsicum annuum L.) development

Nowadays, near-infrared phosphor-converted light emitting diodes (NIR pc-LEDs) attract wide attention since the NIR spectroscopy technique can exert itself in many fields. However, most of the developed NIR phosphors are still not commercially viable, because of low internal/external quantum yield and poor thermal resistance. Therefore, it is urgent to develop an efficient irradiance and thermal stable NIR phosphor. In this work, the new GdAl3-x-yGay(BO3)4: xCr3+ phosphors, compared with the original phosphor (x = 0.03, y = 0), when x = 0.03, y = 0.2, the luminescence intensity increased by 2.1 times, and the thermal resistance jumped from 92.0% to 96.7%. At the same time, with the increase of Ga3+, the spectra were gradually red shifted and FWHM widened, attributing to the nephelauxetic effect and the electron-phonon coupling effect enhanced, respectively. Particularly, under 420 nm excitation, the internal and external quantum yield of GdAl2.77Ga0.2(BO3)4: 0.03Cr3+ were 93.4% and 35.5%, respectively, which is higher than the previous research. The electric-optical conversion efficiency of the pc-LED was 10.76%. Finally, the phosphor application experiments revealed that the prepared phosphor has a very high commercial application potential.

Spectroscopic studies on a natural biomarker for the identification of origin and quality of tea extracts for the development of a portable and field deployable prototype

Even in the era of smart technologies and IoT enabled devices, tea testing technique continues to be a person specific subjective task. In this study, we have employed optical spectroscopy-based detection technique for the quantitative validation of tea quality. In this regard, we have employed the external quantum yield of quercetin at 450 nm (λex = 360 nm), which is an enzymatic product generated by the activity of β-glucosidase on rutin, a naturally occurring metabolite responsible for tea-flavour (quality). We have found that a specific point in a graph representing Optical Density and external Quantum Yield as independent and dependent variables respectively of an aqueous tea extract objectively indicates a specific variety of the tea. A variety of tea samples from various geographical origin have been analysed with the developed technique and found to be useful for the tea quality assessment. The principal component analysis distinctly showed the tea samples originated from Nepal and Darjeeling having similar external quantum yield, while the tea samples from Assam region had a lower external quantum yield. Furthermore, we have employed experimental and computational biology techniques for the detection of adulteration and health benefit of the tea extracts. In order to assure the portability/field use, we have also developed a prototype which confirms the results obtained in the laboratory. We are of the opinion that the simple user interface and almost zero maintenance cost of the device will make it useful and attractive with minimally trained manpower at low resource setting.

Single-Particle Measurements Reveal the Origin of Low Solar-to-Hydrogen Efficiency of Rh-Doped SrTiO3 Photocatalysts.

Solar-powered photochemical water splitting using suspensions of photocatalyst nanoparticles is an attractive route for economical production of green hydrogen. SrTiO3-based photocatalysts have been intensely investigated due to their stability and recently demonstrated near-100% external quantum yield (EQY) for water splitting using wavelengths below 360 nm. To extend the optical absorption into the visible, SrTiO3 nanoparticles have been doped with various transition metals. Here we demonstrate that doping SrTiO3 nanoparticles with 1% Rh introduces midgap acceptor states which reduce the free electron concentration by 5 orders of magnitude, dramatically reducing built-in potentials which could otherwise separate electron-hole (e-h) pairs. Rhodium states also function as recombination centers, reducing the photocarrier lifetime by nearly 2 orders of magnitude and the maximum achievable EQY to 10%. Furthermore, the absence of built-in electric fields within Rh-doped SrTiO3 nanoparticles suggests that modest e-h separation can be achieved by exploiting a difference in mobility between electrons and holes.

Synthesis and optical properties of highly efficient Na3KMg7(PO4)6:Eu2+ blue phosphor for full-spectrum white-light-emitting diodes: The role of Li2CO3 flux

Full-spectrum phosphor-converted white-light-emitting diodes (pc-WLED) are emerging as a mainstream technology in semiconductor lighting. Nevertheless, high-performance blue phosphor which can be excited efficiently by a 400 nm NUV diode chip is still lacking. Herein, we present a blue-emitting Na3KMg7(PO4)6:Eu2+ phosphor synthesized by the solid-reaction method. Particularly, we find that the using of Li2CO3 as flux can significantly improve the crystal quality and thus the emission efficiency of the phosphor. Meanwhile, the excitation peak of the phosphor shifts from 365 to 400 nm, which is pivotal for efficient NUV (400 nm) diode chip excitation. The practical Eu2+ concentration is also enhanced by using Li2CO3 as flux, and the absorption efficiency is greatly increased. This phosphor exhibits superior PL thermal stability, namely retains 94% integrated photoluminescence intensity at 150 °C of that at 25 °C. As a result, the optimized phosphor shows an emission band peaked at 437 nm with a bandwidth of 40 nm and a high external photoluminescence quantum yield of 51.7%. Finally, a pc-WLED was fabricated by using NKMPO:Eu2+ blue, Sr2SiO4:Eu2+ green, CaAlSiN3:Eu2+ red phosphors, and a 400 nm NUV diode chip. It shows a high color rendering index of Ra = 96.4 and a correlated color temperature of 4358 K. These results prove that NKMPO:Eu2+ is a promising blue phosphor for full-spectrum WLED based on NUV diode chips.

On the Quantum Yield Determination of UV Emitting Up-Converters.

This work deals with the determination of the external quantum yield of some selected inorganic up-conversion materials, which are able to convert blue light, as typically emitted using blue (In,Ga)N LEDs, into UV radiation. Recently, these materials have drawn tremendous attention due to their potential application in antimicrobial coatings of surfaces. To judge the viability of this approach to reduce the density of germs onto arbitrary surfaces upon indoor or outdoor illumination, the quantum efficiency for the conversion of blue light into UV is of large interest. We found that the quantum efficiency is between about 0.1% and 1%, which might be good enough if the illumination of the respective surface is performed for several hours. Then, a relevant reduction of the number of active microorganisms per area can be achieved.