Phosphors in LED packages can experience much higher temperatures (>100°C) and light fluxes (>10 W/cm2) versus
traditional phosphors in fluorescent lighting. These conditions place stringent restrictions on LED phosphor selections
and requires, to some extent, an understanding of the potential quenching mechanisms that occur within LED packages.
In this report, we discuss flux-based and temperature-based quenching of LED phosphors, the measurements used to
analyze these quenching processes, and some of the basic mechanisms behind this. It is shown that flux-based
quenching in LEDs can be reasonably anticipated through simple design parameters. However, while it is more difficult
to a priori predict the thermal quenching of new phosphors and their modifications, it is possible to make initial
conclusions about phosphor design through a combination of spectroscopic measurements and chemical inference. This
is specifically demonstrated within the Ce3+-doped garnet family of phosphors, where there is significant flexibility to
modify compositions, leading to initial relationships between composition, emission color, and high temperature
quenching.
Currently, the highest color rendering index (CRI) value obtained in commercially available LED devices is around 90. This falls short of the CRI values typical for incandescent lamps (defined at 100). Similarly, the commercially available LEDs for higher color temperature have CRI values of 65-85, well below the theoretical maximum of 100. New phosphor blends are proposed for use with LED chips emitting in the 350-450 nm range. The application of such blends can afford CRI values greater than 95, over the entire range of color temperatures of interest for general illumination (2500K -
8000K). In some cases, the CRI values approach the theoretical maximum of 100. LED based lamps with a steady state performance of 23 LPW and 25 lumens per chip at 3000K, with a general CRI (Ra) of 97 and a mean CRI (R1-R14) of 96 are demonstrated.
KEYWORDS: Near ultraviolet, Light emitting diodes, Statistical analysis, Ultraviolet radiation, Ultraviolet light emitting diodes, Monte Carlo methods, Europium, Standards development, Spectral models, RGB color model
The advantages of near UV LED chips with phosphors for white light generation are discussed. Recently developed UV LED excitable phosphor blends are presented. Monte Carlo simulations suggest low color point variation (entirely within the first MacAdam oval) for the standard LED chip bin (400-410 nm), compared to high color point variation (outside the fourth MacAdam oval) for the standard bin (460-470 nm) and typical phosphors, modeled as Gaussians of realistic spectral width and targeting the 3000K ANSI color point (x=0.440, y=0.403). A discussion of the full LED package performance is also offered.
The luminescence of Ce3+ in host lattices based on Y3Al5O12 garnets that can be used in blue LED based solid state lighting sources is discussed. Specifically, the effect of Ga3+ and Tb3+ substitution for Al3+ and Y3+, respectively, on the emission color and thermal quenching of these phosphors is described with the initial implications for white light devices.
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