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Abstract
Abstract We report on the methodology and implementation of a robust and accurate double integrating sphere system for measuring the absolute photoluminescence quantum yield and its temperature dependence of commercially available phosphors (garnets, silicates and nitrides). The potential of our instrument for the examination of light interaction with samples of different absorption and diffusion coefficients is also presented, as optical properties of luminescent materials have a major impact on the efficiency of LED’s packaging. Our work gives special attention to the control and the optimization of light losses in the optical system in order to ensure reliable measurements. The YAG:Ce phosphor shows the highest luminescence quantum yield at 97% efficiency, the green silicate the lowest with 79% efficiency. Silicate phosphors show up to 15% loss of luminescence intensity when temperature is raised to 140°C.
Highlights
Phosphor down conversion is the most common strategy to achieve white light using blue Light Emitting Diodes (LED) and phosphors
Our choice for a double integrating sphere system, instead of a single sphere system, was driven by the fact that with our set-up, reflected and transmitted light from the sample can be simultaneously measured within the same experimental conditions and configuration
We have presented the development of a robust instrument for the metrological evaluation of optical properties of solid samples or turbid media
Summary
Phosphor down conversion is the most common strategy to achieve white light using blue Light Emitting Diodes (LED) and phosphors. Among the simplest and most commonly used methods, there is the use of the well-known yellow YAG:Ce phosphor (with a reputed high quantum efficiency) pumped by a blue (450–460 nm) wavelength source. This easy and efficient method produces a white LED with a color rendering index (CRI) of 70–80. A limited number of phosphors are known to be suitable as conversion materials due to the multiple requirements needed to fulfill this conversion task Their excitation and emission spectra have to be of adequate broadness and energies in order to yield the required color rendering index and luminous efficiency. They should present a small particle size distribution and show a homogeneous spherical morphology in order to reduce scattering, to improve quantum yield and to be mixed in silicones, epoxy or other resin matrixes [1,2]
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