High Efficiency Solid State Lighting Research Articles

Microwave-assisted fabrication of Sr2ZnMoO6:Sm2O3 phosphors in TeO2: ZnO: B2O3 glass matrix for high-efficiency solid-state lighting applications

The present work focuses on synthesizing Sr2ZnMoO6:Sm2O3 phosphor-mixed TeO2: ZnO: B2O3 glass by microwave synthesis technique at different times (16, 18, 20, 22, 24 min). These samples, after synthesizing they were characterized through XRD, FTIR, density, molar volume, refractive index, absorption spectra, luminescence properties, and lifetime analysis.The study of crystalline nature was studied using XRD spectra of Sr2ZnMoO6. Absorption spectra were evaluated in the wavelength region between 400 and 1800 nm and found seven peaks, which corresponded with the energy transitions of Sm3+ion from the ground level of 6H5/2 → 6F11/2, 9/2, 7/2, 5/2, 3/2, 6H15/2, and 6F1/2 at 944, 1083, 1238, 1383, 1485 and 1543 nm respectively. The photoluminescence in the wavelength region of 500–750 nm using the excitation wavelength at 403 nm. The emission intensity of the samples increased with sintering time until 20 min after which it decreased. The highest peak was observed at 597 nm, corresponding to 4G5/2 → 6H7/2 (orange) transitions of Sm3+ ion. The luminescence lifetime from the 4G5/2 to 6H7/2 level increased with increasing sintering time until 20 min, which had a lifetime of 0.431–0.711 ms when monitored at λex = 403 nm. The results obtained in photoluminescence properties showed that the samples could be potential candidates for orange light-emitting diodes for solid-state lighting applications.

All-inorganic liquid phase quantum dots and blue laser diode-based white-light source for simultaneous high-speed visible light communication and high-efficiency solid-state lighting: publisher’s note

All-inorganic liquid phase quantum dots and blue laser diode-based white-light source for simultaneous high-speed visible light communication and high-efficiency solid-state lighting: publisher’s note

All-inorganic liquid phase quantum dots and blue laser diode-based white-light source for simultaneous high-speed visible light communication and high-efficiency solid-state lighting.

In recent years, cesium lead bromide (CsPbBr3) and cadmium selenide/zinc sulfide (CdSe/ZnS) quantum dots have been widely investigated to enhance the capacity of visible light communication (VLC) and solid-state lighting (SSL). Herein, liquid-phase color converter (LCC) glass cavities and solid-phase color converter (SCC) films with green-emitting CsPbBr3 and red-emitting CdSe/ZnS are fabricated to investigate and compare their performance. A facile high-quality LCC-based white laser diode (WLD) is fabricated by combining blue LD with LCC CsPbBr3 and CdSe/ZnS glass cavities as color conversion layers. The LCC-based WLD achieves bright white light with a color rendering index of 85, a correlated color temperature of 5520 K, and a Commission Internationale de L'Eclairage (CIE) coordinates at (0.32, 0.34). Moreover, the VLC system exhibits a modulation bandwidth of 855 MHz and the capability to transmit a real-time data rate of up to 2.1 Gbps over a transmission distance of 1.2 meters. These results indicate that the fabricated WLD is a promising lighting device for simultaneous high-speed VLC and high-efficiency SSL.

Highly-efficient all-inorganic lead-free 1D CsCu2I3 single crystal for white-light emitting diodes and UV photodetection

Abstract Lead-based halide perovskites have received great research interest in producing exceptional optoelectronic devices owing to their superior photophysical properties. However, inclusion of toxic Pb in these perovskites brings great risk to public health and hinders their use. Here we report the use of copper(I) to fully substitute Pb to produce Pb-free one-dimensional (1D) CsCu2I3 single crystals (SCs). High-quality, air stable, and yellow-emitting 1D CsCu2I3 SC with length as long as 13 mm is synthesized via inverse temperature crystallization method. A record photoluminescence quantum yield (PLQY) first exceeding 50% (50.4%) is obtained with oleic acid as additive during growth. White light-emitting diodes produced by using the 1D CsCu2I3 SC as yellow phosphors are strikingly capable of working continuously for more than 580 h with a half-lifetime of ~150 h in air. Photodetectors fabricated by the 1D CsCu2I3 SC show distinct UV response with fast response time as low as 50.4 ms (at 340 nm). Our findings pave a way by using the copper(I)-based 1D CsCu2I3 SCs for future high-efficiency solid-state lighting and fast UV photodetection applications.

High-Bandwidth White-Light System Combining a Micro-LED with Perovskite Quantum Dots for Visible Light Communication.

This work proposes a high-bandwidth white-light system consisting of a blue gallium nitride (GaN) micro-LED (μLED) exciting yellow-emitting CsPbBr1.8I1.2 perovskite quantum dots (YQDs) for high-speed real-time visible light communication (VLC). The packaged 80 μm × 80 μm blue-emitting μLED has a modulation bandwidth of ∼160 MHz and a peak emission wavelength of ∼445 nm. The achievable bandwidth of the white-light system is up to 85 MHz in the absence of filters and equalization technology. Meanwhile, the bandwidth of the YQDs as a color converter is as high as 73 MHz with the blue GaN μLED as the pump source. A maximum data rate of 300 Mbps can be achieved by taking advantage of the high bandwidth of the white-light system using the non-return-to-zero on-off keying (NRZ-OOK) modulation scheme. The resultant bit-error rate is 2.0 × 10-3, well beneath the forward error correction criterion of 3.8 × 10-3 required for error-free data transmission. In addition, the YQDs which we proposed as a color converter possess high stability for VLC. After half a year, the achievable bandwidths of the white-light system and the YQDs are still up to 83 and 70 MHz, respectively. This study provides the direction of developing high-bandwidth white-light system for both high-efficiency solid-state lighting and high-speed VLC.

Reliable, All-Phosphorescent Stacked White Organic Light Emitting Devices with a High Color Rendering Index

High efficiency solid state lighting devices have the potential to significantly reduce lighting energy usage while also offering good color rendering and longer lifetimes than conventional lighting sources. While organic light emitting diodes are promising candidates for this application, their operational lifetime is limited by the blue phosphorescent chromophore. We demonstrate stacked white phosphorescent light emitting devices (SWOLEDs) with lifetimes (as determined from the time it takes to lose 30% of the initial luminance of 1000 cd/m2) of up to 80000 h. The correlated color temperature of the devices ranges between 2780 and 3300 K, with color rendering index as high as 89. The three emitter (red, green, and blue) devices contain up to five stacked elements and employ red emitting blocking layers, stable charge generation layers, graded doping, and hot excited state management to achieve long lifetime. The materials and layer structures used and design principles for SWOLEDs are discussed.

Defect-induced infrared electroluminescence from radial GaInP/AlGaInP quantum well nanowire array light- emitting diodes

Radial GaInP/AlGaInP nanowire array light-emitting diodes (LEDs) are promising candidates for novel high-efficiency solid state lighting due to their potentially large strain-free active emission volumes compared to planar LEDs. Moreover, by proper tuning of the diameter of the nanowires, the fraction of emitted light extracted can be significantly enhanced compared to that of planar LEDs. Reports so far on radial growth of nanowire LED structures, however, still point to significant challenges related to obtaining defect-free radial heterostructures. In this work, we present evidence of optically active growth-induced defects in a fairly broad energy range in vertically processed radial GaInP/AlGaInP quantum well nanowire array LEDs using a variety of complementary experimental techniques. In particular, we demonstrate strong infrared electroluminescence in a spectral range centred around 1 eV (1.2 μm) in addition to the expected red light emission from the quantum well. Spatially resolved cathodoluminescence studies reveal a patchy red light emission with clear spectral features along the NWs, most likely induced by variations in QW thickness, composition and barriers. Dark areas are attributed to infrared emission generated by competing defect-assisted radiative transitions, or to trapping mechanisms involving non-radiative recombination processes. Possible origins of the defects are discussed.

Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs.

High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This “compliant” buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 105 cm−2. In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6” wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors.

Photoluminescence Imaging of Semiconductors

The development of energy-related devices requires new materials and fabrication processes that enable both an enhancement in performance and a decrease in manufacturing cost. Polycrystalline semiconductors are promising for photovoltaic applications because they can be grown at low temperatures on inexpensive substrates. Metamorphic epitaxy of semiconductor alloys on latticemismatched substrates is also increasingly used to access new semiconductor alloys for visible light emitting diodes used in high efficiency solid-state lighting. With these advancements, defects play a progressively more prominent role in device performance, and it is important to be able to probe their behavior in order to understand and ultimately control their effects. Information about the spatial distribution of extended defects and compositional fluctuations as well as their influence on carrier transport is particularly crucial for materials engineering efforts. Characterization techniques must therefore be able to provide real time feedback with micron-scale spatial resolution. We present a novel photoluminescence (PL) imaging technique with both of these capabilities and discuss the information that can be obtained in a number of semiconductor systems.

Guest Editorial Recent Advances in Solid State Lighting

This Special Issue on Solid State Lighting, comprising the April/May/June 2013 issues of the IEEE/OSA Journal of Display Technology, focuses on the material physics and innovations, device physics and simulations, new device concepts and engineering, and system implementation of high efficiency solid state lighting technologies. The 45 papers of this Special Issue on Solid State Lighting covers both the innovations in inorganic and organic LEDs technologies, as well as the new concepts required for system implementation of the technology. We are very fortunate to have several excellent manuscripts in the key topics areas related to the progress for achieving high internal quantum efficiency and novel approaches for improving light extraction in III-Nitride LEDs, new concept for achieving phosphor-converted white LEDs, and key advances in the important field of organic LEDs. The progress in both organic and inorganic LEDs is very important, and the advances are complementary of one another attributed to the different key applications enabled by these two technologies. This Special Issue on Solid State Lighting covers three separate categories: 1) innovations for addressing the internal quantum efficiency and efficiency-droop in III-Nitride LEDs; 2) novel approaches for addressing light extraction efficiency in III-Nitride LEDs, and enabling circuits and systems for LEDs; and 3) novel approaches for white LEDs, and key advances and review on the material and device concepts in organic LEDs.

Complete composition tunability of InGaN nanowires using a combinatorial approach

The III nitrides have been intensely studied in recent years because of their huge potential for everything from high-efficiency solid-state lighting and photovoltaics to high-power and temperature electronics. In particular, the InGaN ternary alloy is of interest for solid-state lighting and photovoltaics because of the ability to tune the direct bandgap of this material from the near-ultraviolet to the near-infrared region. In an effort to synthesize InGaN nitride, researchers have tried many growth techniques. Nonetheless, there remains considerable difficulty in making high-quality InGaN films and/or freestanding nanowires with tunability across the entire range of compositions. Here we report for the first time the growth of single-crystalline In(x)Ga(1-x)N nanowires across the entire compositional range from x=0 to 1; the nanowires were synthesized by low-temperature halide chemical vapour deposition and were shown to have tunable emission from the near-ultraviolet to the near-infrared region. We propose that the exceptional composition tunability is due to the low process temperature and the ability of the nanowire morphology to accommodate strain-relaxed growth, which suppresses the tendency toward phase separation that plagues the thin-film community.

25.1: Invited Paper: Achieving Efficient Solid State Lighting Using Organic Light Emitting Devices

AbstractA significant challenge facing human kind in the 21st Century is how to address the ever decreasing supply of depletable and renewable energy. One approach to this problem is to decrease our usage. for this reason, considerable attention has been focused on more efficient means for room lighting which currently consumes approximately 20% of the total energy used. Organic light emitting devices (OLEDs) provide a unique opportunity to provide this high efficiency solid state lighting at very low cost. In this talk, I will discuss several strategies for achieving very high efficiency white light emission at high brightnesses for the next generation of efficient solid state lighting sources based on small molecular weight, vapor deposited OLED structures. Key to our approach is the use of electrophosphorescence as a means for converting all electrical into optical energy. We show that the highest luminance efficiencies can be obtained by a combination of fluorescence and phosphorescence in a unique OLED structure. Furthermore, the highest brightnesses are achieved (without a significant loss in power efficiency) by stacking several fluorescent/phosphorescent elements in a single OLED structure (called a SOLED), with each emitting element in the stack separated by a transparent charge generation layer. Prospects for OLEDs as the next practical generation of interior illumination sources will be reviewed.