As solid-state lighting adoption moves from bulb socket replacement to lighting system engineering, luminaire manufacturers are beginning to actualize far greater cost savings through luminaire optimization rather than the simplistic process of component cost pareto management. Indeed, there are an increasing number of applications in which we see major shifts in the value chain in terms of increasing the L1 (LED) and L2 (LED array on PCB) value. The L1 value increase stems from a number of factors ranging from simply higher performing LEDs reducing the LED count, to L1 innovation such as high voltage LEDs, optimizing driver efficiency or to the use of high luminance LEDs enabling compact optics, allowing not only more design freedom but also cost reduction through space and weight savings. The L2 value increase is realized predominantly through increasing L2 performance with the use of algorithms that optimize L1 selection and placement and/or through L2 integration of drivers, control electronics, sensors, secondary lens and/or environmental protection, which is also initiating level collapse in the value chain. In this paper we will present the L1 and L2 innovations that are enabling this disruption as well as provide examples of fixture/luminaire level benefits.
Fully phosphor-converted LEDs (FpcLeds) with saturated emission have been realized in the green and amber spectral
region. With the Lumiramic phosphor technology it is possible to achieve high package efficiency with minimum
transmission of blue light from the primary LED source. This is done by keeping the scattering properties of the
phosphor layer low while the phosphor thickness is chosen to fully convert all blue LED emission. It is shown that this
can be done not only for optically isotropic Lumiramic materials like garnets, but also for oxonitridosilicate materials
like the green emitting Europium doped SrSi2O2N2, crystallizing in a triclinic lattice with three optical axes. The
scattering power of the Lumiramic can be decreased to acceptable levels by increasing the size of the crystallites in the
densely sintered ceramics. Light propagation is found to be described well with Mie scattering of mono-sized SrSi2O2N2
spheres with refraction index differing by 0.07 to the refractive index of a SrSi2O2N2 matrix material. Using this
technology, the green-yellow gap of visible light emitting LEDs can be bridged and color tunable lamps with the
efficiency and flux of today's white phosphor-converted LEDs become feasible.
This paper presents electrical characteristics for high-performance pentacene-based organic field-effect transistors (OFETs) manufactured on polymer substrates. The mobilities as high as 2.13 cm2/V-s are reported for devices with a bottom-contact configuration and solution cast dielectric layers. The influence of the dielectric choice on pentacene structure and carrier mobility as well as a method for the improvement of current injection is discussed.
We have investigated the miniaturization of photonic devices for ultimate photon localization, and have demonstrated two-dimensional photonic crystal nanolasers with two important quantum nanostructures-quantum wells (QWs) and quantum dots (QDs). Photonic crystal cavities with QW active material, are simple, but powerful nanolasers to produce intense laser output for signal processing. On the other hand, when located in a high-quality factor (Q) nanocavity, because QD(s) strongly couple with the intense optical field, QD photonic crystal cavities are expected to be good experimental setups to study cavity quantum electrodynamics, in addition to high speed and compact laser sources. Our photonic crystal nanolasers have shown as small thresholds as 0.12mW and 0.22mW for QD-photonic crystal lasers and QW-photonic crystal lasers, respectively, by proper cavity designs and nanofabrication. For QD-photonic crystal lasers, whispering gallery modes in square lattice were used together with coupled cavity designs and, for QW-photonic crystal lasers, quadrapole modes in triangular lattice with fractional edge dislocations were used to produce high-Q modes with small mode volume.
Carrier and spin dynamics are measured in meutral, positively and negatively charged quantum dots using polarization-sensitive time-resolved photoluminescence. Carrier capture rates are observed to be strongly enhanced in charged quantum dots, suggesting that electron-hole scattering dominates this process. For positive quantum dots, the enhanced spin-polarized electron capture rate eliminates loss of electron spin information in the GaAs barriers prior to capture, resulting in strong circularly-polarized emission. Comparison of spin relaxation times in positively charged and neutral quantum dots reveals a negligible influence of the large built-in hole population, in contrast to measurements in higher-dimensional p-type semiconductors. The long spin life-time, short capture time, and high radiative efficiency of the positively charged quantum dots indicates that these structures are superior to both quantum wells and neutral quantum dots for spin detection using a spin light-emitting diode.
Quantum dot photonic crystal lasers are demonstrated at room temperature by optical pulse pumping. Coupled cavities were designed based on square lattice PC slabs. Optimized two-dimensional photonic crystal cavities were defined in 200nm slabs with five-stacked InAS QDs layers. The two- and four-coupled cavities showed as incident pump power threshold as 120μW and 370μW, respectively, both from QD ground state emission range. Both clear threshold in pump power-output resonance power and resonance line width narrowing were observed from our membrane samples. The measured wavelengths matched very well with wavelengths predicted by 3D-Finite Difference Time Domain modelling.
Carrier dynamics in self-assembled quantum dots, grown by molecular beam epitaxy, have been studied. The temperature dependence of the relaxation times, measured by room temperature high frequency impedance response of quantum dot lasers and by low temperature (T=4K) differential transmission spectroscopy, strongly suggests that electron- hole scattering is the dominant scattering mechanism in quantum dots. The favorable relaxation times can be exploited to realize far infrared emission and detection based on intersubband transitions in the dots.
In this paper we discuss crystal growth, spontaneous emission characteristics and low threshold performance of 1.3 micrometers InGaAs/GaAs quantum dot heterostructure lasers grown using sub-monolayer depositions of In, Ga, and As. Oxide-confinement is effective in obtaining a low threshold current of 1.2 mA and threshold current density of 19 A/cm2 under continuous-wave room-temperature operation. At 4 K a remarkably low threshold current density of 6 A/cm2 is obtained. We also discuss ground state lasing at (lambda) equals 1.07 micrometers of a vertical cavity surface emitting laser in which a stacked and high dot density active region has been incorporated. The high QD density active region is achieved using alternating monolayers of InAs and GaAs. Lasing threshold conditions and gain parameters for a ground state quantum dot vertical cavity laser are also analyzed.