The reduction of the thermal quenching effect in laser-excited phosphor converters using highly thermally conductive hBN particles.

Phosphor converters for solid state lighting applications experience a strong thermal stress under high-excitation power densities. The recent interest in laser diode based lighting has made this issue even more severe. This research presents an effective approach to reduce the thermal quenching effect and damage of laser-excited phosphor-silicone converters using thermally conductive hexagonal boron nitride (hBN) particles. Herein, the samples are analyzed by employing phosphor thermometry based on the photoluminescence decay time, and thermo-imaging techniques. The study shows that hBN particle incorporation increases the thermal conductivity of a phosphor-silicone mixture up to 5 times. It turns out, that the addition of hBN to the Eu[Formula: see text] doped chalcogenide-silicone converters can increase the top-limit excitation power density from 60 to 180 W cm[Formula: see text], thus reaching a 2.5 times higher output. Moreover, it is shown that the presence of hBN in Ce[Formula: see text] activated garnet phosphor converters, may increase the output power by up to 1.8 times and that such converters can withstand 218 W cm[Formula: see text] excitation. Besides, hBN particles are also found to enhance the stability of the converters chromaticity and luminous efficacy of radiation. This means that the addition of hBN particles into silicone-based phosphor converter media is applicable in a wide range of different areas, in particular, the ones requiring a high optical power output density.

Study of YAG : Ce and Polymer Composite Properties for Application in LED Devices.

The cost of the rare-earth metal cerium means that preparation of YAG : Ce is expensive. To overcome this, the garnet could partially be replaced by cheaper alternatives, while retaining the original properties of YAG : Ce. Composites with different polymers such as polyethylene glycol diacrylate (M280) and dipentaerythrityl hexaacrylate (M600) were therefore studied. YAG : Ce and boron nitride were added into the polymer matrix in order to obtain composites with enhanced thermal conductivity, necessary for high-optical-density applications. The physical properties of the composites were measured by using XRD, DSC, SEM, and NMR, and the most important characteristics for LED materials such as emission, excitation, decay time and quantum efficiency were analyzed. An LED prototype was developed to test and demonstrate the composites for practical applications. That developed device exhibited optical properties very close to those comprising a commercial garnet prototype, which was also developed for comparison. The main advantage of the proposed technology is that by using 2 time less the amount of YAG : Ce, almost the same light output was obtained compared to commercial phosphors.