A solid solution strategy helps increase the efficiency of Ce3+ oxyfluoride phosphors for solid‐state white lighting. The use of a phosphor‐capping architecture provides additional light extraction. The accompanying image displays electroluminescence spectra from a 434‐nm InGaN LED phosphor that has been capped with the oxyfluoride phosphor.

A new, highly efficient green oxyfluoride phosphor family Sr2.975−x Ba x Ce0.025AlO4F (SBAF:Ce3+) has been developed as a component of solid state white light emitting diodes (LED). The phosphor emits with a maximum at 502 nm when excited by 405 nm excitation, with a quantum efficiency approaching 100%. When SBAF:Ce3+ (x = 1.0) is incorporated with encapsulant on an ultraviolet (405 nm) LED, greenish-white light with a color rendering index of 62 under a forward bias current of 20 mA is obtained. The results suggest that phosphors deriving from SBAF:Ce3+ have potential for incorporation in formulations for white LEDs and related applications. The preparation and structural and optical characterization of the phosphor family is described. Attempts to understand the origins of the high efficiency on the basis of the thermal quenching characteristics of SBAF:Ce3+ in comparison with related compounds are presented.

Light-emitting diodes are becoming the alternative for future general lighting applications, with huge energy savings compared to conventional light sources owing to their high efficiency and reliability. Polarized light sources would largely enhance the efficiency in a number of applications, such as in liquid-crystal displays, and also greatly improve contrast in general illumination due to the reduction in indirect glare. Here, we demonstrate light-emitting diodes presenting high-brightness polarized light emission by combining the polarization-preserving and directional extraction properties of embedded photonic-crystals applied to non-polar gallium nitride. A directional enhancement of up to 1.8-fold was observed in the total polarized light emission together with a high polarization degree of 88.7% at 465 nm. We discuss the mechanisms of polarized light emission in non-polar gallium nitride and the photonic-crystal design rules to further increase the light-emitting diode brightness. This work could open the way to polarized white-light emitters through their association with polarization-preserving down-converting phosphors. INTRODUCTIONDue to a continuously improved performance, light-emitting diodes (LEDs) are not only the major contender for future general lighting sources, 1 but also play an important role in a growing number of other applications-from backlight for high-efficiency televisions and mobile phone displays, to car lights and headlights-replacing the classical white sources owing to their high efficiency, brightness, reliability and low operation cost. Polarized light sources would largely improve the efficiency of most of these applications: from general illumination, with an improved contrast due to reduced glare, 2 which also minimizes eye discomfort and ultimately eye strain, 3 to highefficiency displays which operate through the spatial modulation of polarized light 4 (for completeness, we also note that polarized light and other forms of artificial light could be harmful for the life of animals and other species relying on natural light cycles to live 5 ). However, common light sources are usually unpolarized, since the electric field of the light emitted has no preferred orientation. This is also the case for most of the nitride-based LEDs commercialized nowadays. A strongly linearly polarized source, however, is obtained in m-plane GaN LEDs where the asymmetric in-plane biaxial stress on the quantum wells (QWs) orients the light emitting dipoles preferentially along the in-plane a direction. Non-polar m-plane GaN LEDs were first developed and more intensively investigated due to the possible reduction of polarization-induced electric fields in the QWs, which for c-plane GaN LEDs degrade their radiative recombination rate as a result of quantum confined stark effects. 6,7 Today, the

An important component to the advent of solid state lighting technology is the development of inorganic crystalline phosphors for efficient conversion of photons from blue light emitting diodes (LEDs) to other visible wavelengths for greater color rendering and “warmer” white lighting. We present the results of a recently developed rare earth doped nitride-based red emitting phosphor, Sr2Si5N8:Eu2+, combined with GaN-based blue emitting LEDs and YAG:Ce phosphor for improved white lighting applications. A unique remote phosphor packaging approach was used in all testing to isolate LED performance from phosphor performance. Luminous efficacies were achieved at 94 lm/W with an improved color rendering index (CRI) of 72, mixing red phosphor with YAG:Ce. The Sr2Si5N8:Eu2+ red emitting phosphor was found to have a low temperature sensitivity (only 28% power reduction at 150 °C) and greater luminous performance at low concentrations in the encapsulant by weight relative to other typical red emitting phosphors.

A near-UV excited, oxyfluoride phosphor solid solution Sr 1.975 Ce 0.025 Ba(AlO 4 F) 1Àx (SiO 5 ) x has been developed for solid state white lighting applications. An examination of the host lattice, and the local structure around the Ce 3+ activator ions through a combination of density functional theory, synchrotron X-ray and neutron powder diffraction and total scattering, and electron paramagnetic resonance, points to how chemical substitutions play a crucial role in tuning the optical properties of the phosphor. The maximum emission wavelength can be tuned from green (l em ¼ 523 nm) to yellow (l em ¼ 552 nm) by tuning the composition, x. Photoluminescent quantum yield is determined to be 70 AE 5% for some of the examples in the series. Excellent thermal properties were found for the x ¼ 0.5 sample, with the photoluminescence intensity at 160 C only decreased to 82% of its room temperature value. Phosphor-converted LED devices fabricated using an InGaN LED (l max ¼ 400 nm) exhibit high color rendering white light with R a ¼ 70 and a correlated color temperature near 7000 K. The value of R a could be raised to 90 by the addition of a red component, and the correlated color temperature lowered to near 4000 K.