Philips

About: Philips is a company organization based out in Vantaa, Finland. It is known for research contribution in the topics: Signal & Layer (electronics). The organization has 68260 authors who have published 99663 publications receiving 1882329 citations. The organization is also known as: Koninklijke Philips Electronics N.V. & Royal Philips Electronics.

Strong Geometrical Dependence of the Absorption of Light in Arrays of Semiconductor Nanowires

Abstract: We demonstrate experimentally that arrays of base-tapered InP nanowires on top of an InP substrate form a broad band and omnidirectional absorbing medium. These characteristics are due to the specific geometry of the nanowires. Almost perfect absorption of light (higher than 97%) occurs in the system. We describe the strong optical absorption by finite-difference time-domain simulations and present the first study of the influence of the geometry of the nanowires on the enhancement of the optical absorption by arrays. Cylindrical nanowires present the highest absorption normalized to the volume fraction of the semiconductor. The absolute absorption in layers of conical nanowires is higher than that in cylindrical nanowires but requires a larger volume fraction of semiconducting material. Base-tapered nanowires, with a cylindrical top and a conical base, represent an intermediate geometry. These results set the basis for an optimized optical design of nanowire solar cells.

Blue emitting iridium complexes: synthesis, photophysics and phosphorescent devices

Abstract: Homoleptic Ir(Fnppy)3 and heteroleptic (Fnppy)2Ir(acac) complexes (n = 3: F3ppy = 2-(3′,4′,6′-trifluorophenyl)pyridine; n = 4: F4ppy = 2-(3′,4′,5′,6′-tetrafluorophenyl)pyridine; acac = acetylacetonate) have been synthesized and their spectroscopic properties investigated. The homoleptic complexes exist as two stereoisomers, facial (fac) and meridional (mer), that have been isolated and fully characterized. Their electrochemical and photophysical properties have been studied both in solution and in the solid state and electroluminescent devices have been fabricated. The emissive layers in devices have been obtained mixing the iridium complexes with a PVK [poly(9-vinylcarbazole)] host matrix, in the presence of the electron carrier Bu-PBD [2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole]. The application of a voltage (5.0–6.5 V) between the electrodes of devices leads to electro-generated blue luminescence which has similar energy to the solution emissions. Interestingly, the stability of the devices made with the homoleptic fluorinated iridium complexes strongly depends on the stereochemistry of these phosphors and high (up to 5.5%) external quantum efficiencies for the fac complexes are measured.

Integrated LED driving device with current sharing for multiple LED strings

Abstract: An integrated LED driving device for multiple LED strings which employs a single linear regulator or other controller and a multiple-output current mirror which is almost independent of the DC input voltage source, almost independent of the transistor's or MOSFET's variations from the semiconductor integration process, and almost independent of temperature variation The multiple-output current mirror includes a plurality of transistors or MOSFETs each of which are integrated on the same substrate, with identical width-to-length channel ratios and with identical source and gate connections The integrated LED driving device provides for automatic current sharing in a DC mode and, alternately, with minimized phase delays in a PWM mode The mirror-output current mirror may include mirror-cascode transistor pairs

Grids or air gaps for scatter reduction in digital radiography: a model calculation.

Abstract: The relative advantages of grids and air gaps for scatter reduction in a digital radiography system were investigated using a theoretical model. In this model the properties of the scatter reduction device are described by primary transmission and selectivity. The signal-to-noise (SNR) improvement factor for fixed exposure to the patient was used as a performance indicator. The results show that the SNR improvement depends strongly on the local scatter fraction; for all practical configurations, however, it stays below a factor of 2. For high scatter fractions, an air gap of 20 cm has about the same effect on SNR improvement as a highly selective grid; for low and medium scatter conditions the air gap performs better than any grid. Additive system noise reduces the SNR improvement factor compared to the case with quantum noise only, the reduction being more pronounced for the grids than for the air gap. The results suggest that the use of an air gap instead of a grid is advantageous in digital radiography systems.

Electric Field Strengths at Totally Reflecting Interfaces

Abstract: Incoming and reflected light waves superimpose to form a standing-wave pattern normal to a reflecting surface. For total internal reflection, a cosine distribution of the electric field amplitude in the denser medium joins onto the exponential distribution of the penetrating field in the rarer medium. The electric field amplitude at the reflecting interface is a maximum at the critical angle and decreases to zero at grazing incidence. In this paper, theoretical expressions are given for the electric field amplitudes, near the surface, which depend both on polarization and on angle of incidence. These expressions enable us to calculate from simple formulas, and without the aid of computers, the reflectivity losses resulting from the interaction of these standing waves with absorbing species, near the surface either in the rarer or denser medium. They also give us physical insight into the nature of the absorption mechanism at the reflecting interface when the reflection is frustrated. This is helpful in the fields of internal reflection optical spectroscopy and fiber optics. Experimental results, which agree with theoretical expectations, are presented. Strongest coupling is obtained by working near the critical angle for either polarization, and the absorption in the rarer medium is greater for parallel polarization than for perpendicular polarization.