We demonstrate the first commercial production–ready white light-emitting diodes (LEDs) for the general illumination market with red colloidal quantum dots (QDs) applied in an on–chip configuration. We show the red QDs with tunable peak emission and narrow full width at half-maximum in combination with a conventional phosphor material can lead to LED conversion efficiency improvements of 5% to 15% over commercial phosphor based LEDs at correlated color temperatures (CCTs) ranging from 5000 to 2700 K. Furthermore, the challenges associated with reliability under high temperature, high blue flux intensity, and high humidity operation have been overcome to meet consumer market requirements. Finally, a demonstrator lamp at 3000 K color temperature and 90 color rendering index (CRI) with QD based LEDs show a larger efficiency gain up to 17%, attributed to the reduced blue LED droop from the lower drive current and the lower heat sink temperature when compared to a standard phosphor based LED lamp output.

Droop, the decrease of efficiency with increased power density, became a major topic with InGaN LEDs, after its introduction in 2007. This paper provides insight into droop in localized center luminescence phosphors, exemplified here by Eu2+ doped materials. This topic is of increasing importance, as high brightness blue LEDs have reached outputs >1 W/mm(2). The nonlinearities in phosphor quantum efficiency result in drive-dependent color point shift and reduc-tion of overall efficiency of phosphor converted white LEDs which utilize Eu2+ activated phosphors. The efficiency quenching can be traced back to two processes, well-known in laser physics, excited state absorption or/and cross relaxation by Foerster/Dexter transfer. Both processes lead to reduction in phosphor efficiency, but they can be differentiated. Understanding the root cause of efficiency quenching opens ways to minimize the practical consequences. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Fully phosphor-converted LEDs (FpcLeds) with saturated emission have been realized in the green and amber spectral region. With the Lumiramic(TM) 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.

Phosphor conversion of light‐emitting diode (LED) radiation has been used in many configurations and combinations to generate white light. The concept of down conversion of, e.g., blue LED emission, offers also the possibility to provide efficient generation of monochromatic, high‐color‐purity light, especially in wavelength ranges in which direct radiation from non‐converted LEDs is relatively inefficient, i.e., in the “yellow gap”. In the case described here, a blue‐emitting LED is ‘fully’ converted to amber emission with a peak wavelength of 595 nm and a color purity of >96%, while demonstrating an external quantum efficiency exceeding that of direct AlGaInP LEDs of the same wavelength by a factor of almost two at room temperature, and the lumen output under equal drive conditions at 85 °C by more than a factor of four. An essential component in this high performance is, besides the choice of the right – nitride – phosphor, the use of this phosphor in a densely sintered ceramic form which has considerable optical advantages over powders. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In our contribution we discuss structure-luminescence property relations of MSi2O2N2:Eu (M = Ba, Sr, Ca) phosphors to explain the differences in excitability, emission band position and width. The differences in Eu2+ site coordination, number and size of sites lead to a shift of emission from M = Ba over M = Sr to M = Ca from cyan to yellow accompanied by an increased Stokes shift. Because of its favourable emission properties with a peak at ~ 538 nm SrSi2O2N2:Eu was selected and optimized as down-conversion material for green pcLEDs. pcLEDs built with LUXEONR thin-film flip chip (TFFC) LEDs show stable color points under a wide range of drive conditions (I ≤ 1A, T ≤ 150°C) as a consequence of the very high conversion efficiency of optimized SrSi2O2N2:Eu color converters. Although cutbacks in color purity have to be made because of the broad band phosphor emission spectrum, efficacies of the discussed green pcLEDs are significantly higher compared to direct green emitting InGaN LEDs.

A new phosphor technology for phosphor converted light-emitting diodes (pcLEDs) is presented. A polycrystalline ceramic plate (Lumiramic (TM)) of Ce (III) doped yttrium gadolinium aluminum garnet (Y,GdAG:Ce) is combined with a blue LED to produce white light in the range of 5000 K correlated color temperature. Scattering and light extraction means of the Lumiramic ceramic color converter plates enable production of reliable and efficient white pcLEDs. Measurement of the optical properties of the Lumiramic plates before the final LED assembly allows pick and place packaging with exact targeting of the desired white color point of the LED. Combination with a red phosphor powder layer, coated onto the Lumiramic plate, results in high quality white pcLEDs with any color temperature required for the general lighting market.