Solid-state Lighting Technology Research Articles

Near-unity emission in zero-dimensional Sb(III)-based halides intervened by hydrogen bonds towards efficient solid-state lighting technology

Zero-dimensional (0D) metal halides have garnered considerable interest owing to their superb optical characteristics, and adaptable architectures. Two 0D organic-inorganic metal halides (OIMHs) (C20H20P)2SbCl5·(EA) ([C20H20P]+ = ethyltriphenylphosphine) and (C20H20P)2SbCl5·(IPA) were successfully synthesized and investigated using a simple solvent-evaporation approach. These OIMHs possess a similar structure, except for the solvent molecules in the lattice, however, their photoluminescence quantum yields (PLQYs) exhibit a considerable difference, with 99.82% in (C20H20P)2SbCl5·(EA) and 73.7% in (C20H20P)2SbCl5·(IPA). Bond-order and crystal orbital Hamilton population (COHP) calculations reveal that (C20H20P)2SbCl5·EA system exhibits stronger hydrogen bonds, leading to stronger supramolecular interactions, which suppress non-radiative transition. The experimental results and density functional theory (DFT) calculations suggest an increase in PLQY, which could be attributed to the stronger hydrogen bonding in (C20H20P)2SbCl5·(EA) resulting in strong interactions between the organic and inorganic components, good mobility, and improved exciton utilization. This study introduces a rational strategy for microstructure optimization, which builds upon solvent modulation to achieve stronger hydrogen bonding and thus improve the PLQY of 0D OIMHs.

On the performance of delta sigma modulators for DCO-OFDM based NOMA visible light communication systems

The revolution of the solid-state lighting technology and the looming radio frequency (RF) spectrum crisis enabled the rapid evolution of visible light communication (VLC) in the recent times. To furnish contemporaneous illumination and communication, VLC relies on white light emitting diodes (WLEDs). However, the limited modulation bandwidth of WLEDs poses a threat to VLC as the achievable data rates are drastically minimized. Eventually, to enhance the achievable throughput, the pre-eminent way is to apply orthogonal frequency division multiplexing (OFDM) to a VLC system. Furthermore, a VLC system can also exploit non-orthogonal multiple access (NOMA) scheme to bestow with seamless services to the multiple users. However, much similar to the RF-based OFDM system, the OFDM-VLC system also inherits one of the serious disadvantages like the high peak to average power ratio (PAPR). In addition, the rapid fluctuations of the continuous time-domain signal amplitude in DC-biased optical OFDM (DCO-OFDM) results in much complicated design of the LED driver circuitry for driving the LED. Thus, to overcome such drawbacks, we incorporate delta-sigma modulators (DSM) to the NOMA-VLC system which is making use of DCO-OFDM, and we analyze its performance over VLC channel environment. The stunning advantage imparted by the proposed DSM-based DCO-OFDM-NOMA-VLC system is that the continuous amplitude of the time-domain transmitted signal is converted into two levels for driving the LED. Additionally, with the major goal to maximize the sum throughput of the proposed multiuser VLC system by taking into consideration both the user fairness as well as the intensity constraints, we derived the optimal values for the power allocation coefficients corresponding to the fair power allocation algorithm. Furthermore, the dynamically varying fair power allocation algorithm is compared with the fixed/static power allocation algorithm. The major contribution of this work is of two-fold: firstly, the proposed DCO-OFDM-NOMA-VLC system which is making use of DSM exhibits a remarkable reduction in PAPR when compared with the conventional system without the application of DSM, where the proposed system demonstrates a significant gain of 4.78 dB in terms of PAPR reduction. Secondly, from the simulated results it can affirmed that the proposed system not only achieves enhanced sum rates and better outage performance but also imparts a better bit error ratio (BER) performance corresponding to the far user.

Cubane Dimerization: Cu4 vs Cu8 Copper Iodide Clusters.

Copper(I) halides are well-known for their structural diversity and rich photoluminescence properties, showing great potential for the development of solid-state lighting technology. A series of four molecular copper iodide clusters based on the [Cu4I4] cubane geometry is reported. Among them, [Cu8I8] octanuclear clusters of rare geometry resulting from dimerization of the tetranuclear counterparts were also synthesized. Two different phosphine ligands were studied, bearing either a styrene or an ethyl group. Therefore, the effect of the dimerization and of the ligand nature on the photophysical properties of the resulting clusters is investigated. The structural differences were analyzed by single-crystal X-ray diffraction (SCXRD), solid-state nuclear magnetic resonance (NMR), infrared, and Raman analyses. Compared to the ethyl group, the styrene function appears to greatly impact the photophysical properties of the clusters. The luminescence thermochromic properties of the ethyl derivatives and the intriguing photophysical properties of the clusters with styrene function were rationalized by density functional theory (DFT) calculations. Thus, the styrene group significantly lowers in energy the vacant orbitals and consequently affects the global energetic layout of the clusters. From this study, it was found that the nuclearity of copper iodide clusters eventually has less influence on the photophysical properties than the nature of the ligand. The design of proper ligands should therefore be considered when developing materials for specific lighting applications.

Structure, photoluminescence, Judd-Ofelt analysis, and thermal stability studies of Eu3+-doped Ba2Tb8(SiO4)6O2 red phosphor with high color purity

In this study, a series of Eu3+-doped Ba2Tb8(SiO4)6O2 red-emitting phosphors were developed by using a conventional solid-state reaction technique. The crystalline structure, surface morphology, photoluminescence properties, energy transfer processes, and thermal behavior of the Eu3+-doped Ba2Tb8(SiO4)6O2 phosphors were studied. The X-ray diffraction patterns confirmed the formation of the phase, and the Rietveld refinement study revealed that the Eu3+-doped Ba2Tb8(SiO4)6O2 phosphors have a hexagonal crystal structure with the space group P63/m. Energy-dispersive X-ray analysis confirmed the homogenous distribution of Eu3+ ions over the Tb3+ sites. Photoluminescence (PL) spectroscopy was used to test the luminescent properties of the synthesized phosphors. The PL spectra showed that upon UV and blue light exposure, the Eu3+-doped Ba2Tb8(SiO4)6O2 phosphors exhibited red emission associated with the 5D0→7FJ transitions. The mechanisms of concentration quenching and energy transfer were analyzed using Blasse and Dexter's formula. Judd-Ofelt parameters (Ω2, Ω4) and other radiative parameters were analyzed using PL emission spectra to investigate the luminescence behavior of Eu3+-doped Ba2Tb8(SiO4)6O2 phosphors. The results of the thermal stability studies show that Eu3+-doped Ba2Tb8(SiO4)6O2 has good thermal properties with a high activation energy of approximately 0.23 eV. The calculated Commission International del'Eclairage coordinates (x = 0.62 and y = 0.36) of the prepared phosphors confirm that the emitted light is in the red portion with a high color purity of about 99.9%. These findings show that Eu3+-doped Ba2Tb8(SiO4)6O2 phosphors are a viable option for solid-state lighting technology.

Optimizing LERP systems: opto-thermal steady-state simulation analysis and experimental validation.

Laser-excited remote phosphor (LERP) systems are the next step in solid-state lighting technology. However, the thermal stability of phosphors has long been a major concern in the reliable operation of these systems. As a result, a simulation strategy is presented here that couples the optical and thermal effects, while the phosphor properties are modeled to temperature. A simulation framework is developed in which the optical and thermal models are defined in Python using appropriate interfaces to commercial software: the ray tracing software Zemax OpticStudio for the optical analysis and the finite element method (FEM) software ANSYS Mechanical for the thermal analysis. Specifically, the steady-state opto-thermal analysis model is introduced and experimentally validated in this study based on Ce:YAG single-crystals with polished and ground surfaces. The reported experimental and simulated peak temperatures are in good agreement for both the polished/ground phosphors in the transmissive and reflective setups. A simulation study is included to demonstrate the simulation's capabilities for optimizing LERP systems.

Performance optimization of Ce:YAG sapphire films for high power density white laser-driven lighting applications

To withstand higher power density (PD), exhibit higher luminous efficiency (LE), use in smaller size and lower cost has become the direction of solid-state lighting technology. In the face of high-density laser irradiation and strong thermal shock, improving the performance of color conversion materials related to laser illumination has become a research hotspot. In this study, The Y3Al5O12:Ce3+ phosphor-in-glass film (Ce:YAG-PiF) was obtained by scraping method. The optimized Ce: YAG-PiF external quantum efficiency (EQE) reaches 74.7%, closing to the phosphor (EQE = 78.47%). Excitingly, at 573 K, the thermal conductivity of sample remains at 9.47 W m−1 K−1. Besides, the sample has an ultra-high LE of 256 lm/W @ 32.47 W/mm2. After recombining with the red phosphor CaAlSiN3:Eu2+ (CASN), the color rendering index (CRI) is 84.6, the correlation color temperature (CCT) is 5594 K, and the LE is 192.91 lm/W @ 39.87 W/mm2. More importantly, the relative intensity of laser module packaged by Ce:YAG & CASN-PiF decreased by 15% when tested at 4 W for 24 h. Besides, the packaged laser flashlight has good collimation within a visible illuminance. All the results show that the prepared sample can maintain high emission intensity at high laser PD and have a good heat resistance, which is a promising color conversion material in the field of solid-state laser illumination.

Interstitial Zinc Boosted Light Tunability, Afterglow, and Ultrabright White Emission in Zinc Germanate (Zn2GeO4)

To reduce the burden of solid-state lighting and phosphor-converted light-emitting diode technologies on rare earth (RE) and avoid their potential supply risks, we have developed a RE-free Zn2GeO4 (ZGeO) microcrystalline phosphor. It was synthesized by a simple and scalable solid-state reaction of ZnO and GeO2 at 1200 °C. High-temperature synthesized ZGeO demonstrated color tunable emission from bluish-white to green on changing the excitation wavelength from 265 to 335 nm with a photoluminescence quantum yield of 42 and 9%, respectively. They could also convert highly energetic X-ray to bluish-green light emission. First-principles calculations showed that bluish-white and green light emissions are linked to zinc interstitials present, respectively, in zinc (Zni2) and zinc–germanium rings (Zni1). These defects generated in large numbers via high-temperature annealing along with antisites boosted the generation of trapping centers leading to dual persistent luminescence (PerL) of white and green light for more than 60 min as well as exhibited radioluminescence. Luminescent ink based on ZGeO was fabricated and successfully tested for anticounterfeiting applications. An extra effort has been vested on making this solid-state processed ZGeO dispersible in water-soluble deep eutectic solvent which could be a game changer for its marketability. This material has great potential to become an efficient RE and dopant-free phosphor synthesized by a simple, scalable, and cost-efficient route for applications in solid-state lighting, display, and anticounterfeiting, having multifunctionalities such as PerL, tunability, and RL.

Investigating defects in InGaN based optoelectronics: from material and device perspective

III-nitride optoelectronics have revolutionized solid-state lighting technology. However, non-radiative defects play a major bottleneck in determining the performance of InGaN-based optoelectronics devices. It becomes especially challenging when high indium is required to be incorporated to obtain emission at higher wavelength (>500 nm). In this research article, we are going to discuss our investigation on the origin of defects in InGaN-based optoelectronics devices from the material and device perspective and characterize them through various techniques. This article broadly consists of two parts. In the first part, we investigate defects in InGaN based optoelectronics from a material point of view. Here, we discuss the challenges in the growth of InGaN planar (2-dimensional) and nanowires (1-dimensional) with high indium (≥20%) incorporation using the plasma-assisted molecular beam epitaxy (PA-MBE) technique. Photoluminescence spectroscopy (PL) has been performed to characterize these grown samples to assess their optical quality. Atomic force microscopy (AFM) has been employed to characterize the surface morphology of grown InGaN layers. High-resolution transmission electron microscopy (HRTEM) and scanning electron microcopy (SEM) are also used to characterize InGaN planar and nanowire samples grown under various process conditions. In the second part, we investigate the role of defects on InGaN optoelectronics from a device point of view. Here, we discuss the fabrication of InGaN multi-quantum well-based light emitting diodes (LEDs). Temperature-dependent current versus voltage measurements are carried out to investigate the role of defects on carrier dynamics under forward and reverse bias conditions. Frequency-dependent capacitance versus voltage (CV) and conductance versus voltage (GV) techniques are employed extensively to characterize defects in fabricated InGaN LEDs.

Judd-Ofelt Analysis and Emission Properties of Dy3+ Ions in Borogermanate Glasses.

Borogermanate glasses singly doped with Dy3+ ions were synthesized and then studied using the absorption and luminescence spectra. Spectroscopic changes of Dy3+ ions have been examined for compositional-dependent glasses with various molar ratios GeO2:B2O3. In this work, several spectroscopic parameters of Dy3+ ions were obtained experimentally and compared to the calculated values from the Judd-Ofelt theory. Luminescence spectra measured for borogermanate glasses consist of blue, yellow and red bands, which correspond to 4F9/2 → 6H15/2, 4F9/2 → 6H13/2 and 4F9/2 → 6H11/2 transitions of Dy3+, respectively. Luminescence lifetimes for the 4F9/2 excited state are reduced, whereas the stimulated emission cross-sections for the most intense 4F9/2 → 6H13/2 yellow transition of Dy3+ increase with increasing GeO2 and decreasing B2O3 concentrations in glass-hosts. Quantum efficiency of the 4F9/2 (Dy3+) excited state is nearly independent on molar ratios GeO2:B2O3. Attractive spectroscopic properties related to the 4F9/2 → 6H13/2 transition of Dy3+ ions are found for borogermanate glasses implying their potential utility for yellow laser action and solid-state lighting technology.

A warm-white light-emitting diode based on single-component emitter aromatic carbon nitride

Artificial lighting consumes almost one-fifth of global electricity. As an efficient solid-state lighting technology, white light-emitting diodes (WLEDs) have received increasing attention. However, the white luminescence of the traditional WLEDs comes from multi-component emitters, which leads to complex device structure and unstable emitting color. Therefore, developing single-component materials with white-light electroluminescence is of significance for artificial lighting applications. Here, we fabricate single-component white-light electroluminescence devices based on an aromatic carbon nitride material and improve the performance of WLEDs by adjusting the carrier transport. The carbon nitride LEDs emit warm-white light, of which color coordinates and color temperature are (0.44, 0.52) and 3700 K. The optimized LEDs display a very low turn-on voltage of 3.2 V and achieve a milestone in the maximum luminance and external quantum efficiency of 1885 cd m−2 and 1.20%. Our findings demonstrate the low-cost carbon nitride materials have promising potential for single-component WLEDs application.

(Digital Presentation) Red and Near-Infrared Emission of Eu2+ Doped Solid-State Phosphors for LED Applications

Owing to the unique 4f-5d transition, Eu2+ is one of the most commonly used activators in luminescent materials for phosphor-converted light-emitting diodes (pc-LEDs), and Eu2+-doped phosphors exhibit outstanding luminescence properties, including multi-color emission, adjustable bandwidth, excellent thermal stability as well as high luminescence efficiency. These attributes motivate scientists to find Eu2+ doped phosphors that can practically meet the various LED application requirements. In this talk, I will summrize our recent progresses to manipulate Eu2+ emission exhibiting red and near-infrared emissions under blue light excitation. One can expect and further adopt proper structural engineering strategies to tune the Eu2+ luminescence. Moreover, the state-of-the-art LED application including solid-state lighting and near infrared night-vision technologies will be also introduced based on these Eu2+ doped phosphors. We hope this talk will be helpful for controlling the photoluminescence by theory-structure-property relationships and guide scientists discover the next generation of Eu2+ doped phosphors for emerging applications.

Approach for Designing Human-Centered and Energy Saving Lighting Luminaires

Electric light has been widely adopted in numerous applications, including signage, display, and illumination. Enhancing its efficiency and quality has been the focal point until now. Long exposure to intensive blue-light-enriched white light is, however, likely to cause health concerns, such as retina damage and melatonin suppression. A good light should hence be redefined as, at least, human-friendly, besides energy-saving and high-quality. Here, we demonstrate a novel design approach toward a good light based on the state-of-the-art solid-state lighting technologies. Taking the typical phosphor converted white-light-emitting diode (LED) for lighting, for example, a 2000 K orange-white emission with a black-body-radiation chromaticity can be 5 times safer than the 5000 K pure-white counterpart from a retina-protection perspective and 3.9 times safer from an MLT-secretion perspective. Further tuning its chromaticity from black-body-radiation- to sunlight-style, the 2000 K LED can be made 303% safer in terms of maximum retina permissible exposure limit or 100% better in terms of melatonin suppression sensitivity. Moreover, its corresponding efficacy limit can be increased from 270 to 285 lm/W, while keeping light quality constant at 91, in terms of natural light spectrum resemblance index. The same approach can be extended to organic LED as well as the design of a good light for display, wherein pure-white emission with a color temperature around 6000 K is suggested to replace the bluish-white backlight to safeguard human health.

A Red-Emitting Cu(I)–Halide Cluster Phosphor with Near-Unity Photoluminescence Efficiency for High-Power wLED Applications

Solid-state lighting technology, where light-emitting diodes (LEDs) are used for energy conversion from electricity to light, is considered a next-generation lighting technology. One of the significant challenges in the field is the synthesis of high-efficiency phosphors for designing phosphor-converted white LEDs under high flux operating currents. Here, we reported the synthesis, structure, and photophysical properties of a tetranuclear Cu(I)–halide cluster phosphor, [bppmCu2I2]2 (bppm = bisdiphenylphosphinemethane), for the fabrication of high-performance white LEDs. The PL investigations demonstrated that the red emission exhibits a near-unity photoluminescence quantum yield at room temperature and unusual spectral broadening with increasing temperature in the crystalline state. Considering the excellent photophysical properties, the crystalline sample of [bppmCu2I2]2 was successfully applied for the fabrication of phosphor-converted white LEDs. The prototype white LED device exhibited a continuous rise in brightness in the range of a high bias current (100–1000 mA) with CRI as high as 84 and CCT of 5828 K, implying great potential for high-quality white LEDs.

All-carbon stretchable and cavity-free white lasers.

Flexible, stretchable, and bendable electronics and optoelectronics have a great potential for wide applications in smart life. An environmentally friendly, cost effective and wide-angle emission laser is indispensable for the emerging technology. In this work, circumvent the challenge issue, cavity-free and stretchable white light lasers based on all carbon materials have been demonstrated by integration of fluorescent carbon quantum dots (CQDs) and crumpled graphene. The typical emission spectrum of the cavity-free laser based on all-carbon materials has a CIE chromaticity coordinate of (0.30, 0.38) exhibiting an intriguing broadband white-light emission. The unprecedented and non-toxic stretchable and white light cavity-free lasers based on all-carbon materials can serve as next-generation optoelectronic devices for a wide range application covering solid-state lighting and future wearable technologies.

Regulating the Singlet and Triplet Emission of Sb3+ Ions to Achieve Single-Component White-Light Emitter with Record High Color-Rendering Index and Stability.

The rapid development of solid-state lighting technology has attracted much attention for searching efficient and stable luminescent materials, especially the single-component white-light emitter. Here, we adopt a facile ion-doping technology to synthesize vacancy-ordered double perovskite Cs2ZrCl6:Sb. The introduction of Sb3+ ions with a 5s2 active lone pair into Cs2ZrCl6 host stimulates the singlet (blue) and triplet (orange) states emission of Sb3+ ions, and their relative emission intensity can be tuned through the energy transfer from singlet to triplet states. Benefiting from the dual-band emission as a pair of perfect complementary colors, the optimum Cs2ZrCl6:1.5%Sb exhibits a high-quality white emission with a color-rendering index of 96. By employing Cs2ZrCl6:1.5%Sb as the down-conversion phosphor, stable single-component white light-emitting diodes with a record half-lifetime of 2003 h were further fabricated. This study puts forward an effective ion-doping strategy to design single-component white-light emitter, making practical applications of them in lighting technologies a real possibility.

Structural Interpretation and Photoluminescence Properties of Sr0:90􀀀xCa0:10Al12O19:Dyx 3+Nanophosphors Synthesis by Combustion system

Objectives: To synthesize a phosphor of more intense, high color purity, and to last longer. Methods: We have synthesized Sr0:90􀀀xCa0:10Al12O19:Dy3+ x (x=0.00, 0.01, 0.03, 0.05, 0.07) phosphors using a low temperature (560  10 )◦C combustion system. X-ray diffraction, Field Emission Scanning Electron Microscopy (FE-SEM), and EDS spectra were used to perform phase identification, morphological examination, and elemental analysis. Spectroscopic photoluminescence techniques of the described phosphor were used to investigate its optical properties. Findings: According to scherrer’s formula, the crystal size of strontium calcium aluminates phosphor is between 12.58 and 84.67 nm. The Dy3+ emission peaks at 475 nm (blue), 573 nm (yellowgreen), and 666 nm (red) in the phosphor. PL emission spectra can be attributed to the 4f-4f transition of Dy3+ ions. The phosphor color purity is 15%, and the average life time is 0.96 ms, indicating that it will survive a long last. The intensity at the wavelengths of 475nm and 575 nm is 40000 counts and 35000 counts, respectively. Novelty: With a 0.10 molar calcium concentration, we have synthesized strontium aluminates phosphor with improved properties. The described phosphor has long-lasting applications as a refractory structural material, great and useful material for pale-orange colorants, and may be employed in many solid-state lighting technologies. Keywords: Strontium Aluminates Phosphor; Paleorange Phosphor; Photoluminescence; Correlated Color Temperature; Combustion System

High efficiency green-emitting phosphor-in-glass films for high-power solid-state laser lighting

The next generation of solid-state lighting technology driven by laser diodes (LDs) is in full development, and the way green fluorescent materials with narrow-band emission (such as β-Sialon) exert their inherent potential in laser displays and projectors has attracted public interest. In this paper, stable borosilicate glass was utilized as an inorganic binder to prepare phosphor-in-glass films (PiFs) by cosintering sapphire and β-Sialon phosphor. There was no interface reaction between the glass and the phosphor, and the phosphor was uniformly and nondestructively distributed in the composite film closely attached to the sapphire. The optimized PiFs achieved an internal quantum efficiency of 76% and a thermal conductivity of 8.6 W m−1K−1, and a thermal diffusivity of 2.6 mm2 s−1 demonstrated their excellent thermal stability. A beam of high-purity light with a brightness of 887 lm and a luminous efficiency of 183 lm/W was achieved under 450 nm blue LD radiation, which is the relatively superior performance by β-Sialon series luminescent materials in an LD application reported thus far. We believe that in the near future, strategies such as adjusting glass composition, improving quantum efficiency, and sample postprocessing will further improve the performance of β-Sialon phosphors with narrow-band emission to make new contributions in the field of high-quality lasers.

Anti-Defect engineering toward high luminescent efficiency in whitlockite phosphors

Lacking an effective strategy to simultaneously address the challenges of quantum efficiency, luminescence intensity and thermal stability has become the key bottleneck for further development and large-scale application of solid-state lighting technology. Herein, inspired by the defect-engineering used in photoelectrocatalytic and photovoltaic materials, we acted in a diametrically opposite way and unprecedentedly proposed an anti-defect engineering strategy to develop high-efficiency phosphors. By constructing a rigid structure and introducing alkali metals M to remove cation vacancy defects, similar to building blocks and jigsaw puzzle, we developed three groups of whitlockite phosphors, namely Ca3-xSrx(PO4)2:Ce3+, Ca3(PO4)2:Ce3+,M and (Ca0.5Sr0.5)3(PO4)2:Ce3+,Na+,Mn2+, and synchronously realized the significant enhancement of photoluminescence intensity (2.46 times), thermal stability (87.92% at 150 °C), cathodoluminescence intensity (3.34 times), quantum yield (from 38.90% to 99.07%). We characterized the defect concentration by positron annihilation technique (PAT), and calculated Debye temperature (ΘD) and simulated the occupation of M according to DFT theory to reveal the improvement mechanism. Some advanced applications were also explored in this work, including warm-white LEDs, plant growth lighting and information security. The anti-defect engineering proposed in this work may contribute to the further development of high-efficiency phosphors for the next-generation smart solid-state lighting technologies.

Ni2+-Doped Garnet Solid-Solution Phosphor-Converted Broadband Shortwave Infrared Light-Emitting Diodes toward Spectroscopy Application.

Broadband shortwave infrared (SWIR) light-emitting diodes (LEDs), capable of advancing the next-generation solid-state smart invisible lighting technology, have sparked tremendous interest and will launch ground-breaking spectroscopy and instrumental applications. Nevertheless, the device performance is still suppressed by the low quantum efficiency and limited emission bandwidth of the critical phosphor layer. Herein, we report a high-performance Ni2+-doped garnet solid-solution broadband SWIR emitter centered at ∼1450 nm with a large full-width at half-maximum of ∼300 nm, thereby fabricating, for the first time, a directly excited Ni2+-doped garnet solid-solution phosphor-converted broadband SWIR LED device. A synergetic enhancement strategy, adding a fluxing agent and a charge compensator simultaneously, is proposed to deliver a more than 20-fold increase of the SWIR emission intensity and nearly 2-fold improvement of the thermal quenching behavior. The site occupation and mechanism behind the synergetic enhancement strategy are elucidated by a combination of experimental study and theoretical calculation. A prototype of the SWIR LED with a radiation flux of 1.25 mW is fabricated and utilized as an invisible SWIR light source to demonstrate the SWIR spectroscopy applications. This work not only opens a window to explore novel broadband SWIR phosphors but also provides a synergetic strategy to remarkably improve the performance of artificial SWIR LED light sources.

Enhanced light extraction from organic light emitting diodes using a flexible polymer-nanoparticle scattering layer

Efficient optical outcoupling from organic light emitting diodes (OLEDs) is an important challenge in solid state lighting technology. In this work, the effect of an external light extraction layer, prepared using polydimethylsiloxane (PDMS) and zinc oxide (ZnO) nanoparticles, was studied on the performance of red, green, blue and white OLEDs. The self-standing flexible film can effectively address the loss modes at the substrate-air interface. With the application of the layer, a maximum enhancement of about 80% in light outcoupling was observed in white OLEDs. Monochrome OLEDs also showed appreciable enhancement in emission with green having the highest improvement (102%), followed by red (56%) and blue (35%). Finite-difference time-domain (FDTD) simulations were performed for elucidating the mechanism behind the improvement in light extraction due to nanoparticle scattering layer. Total-Field Scattered-Field (TFSF) source was used to simulate the scattering cross-section for different wavelengths. Reduced Fresnel reflections at the air-glass interface and advantageous Mie scattering by ZnO nanoparticles seem to increase the optical outcoupling. This film could be a potential candidate for light extraction in OLEDs because of its facile fabrication, economical precursors, and adaptability to flexible substrates and absence of any possible optical artefacts to the emission.