| Abstract [eng] |
Investigation of Optical and Thermal Properties of Composite Phosphor Matrices Solid state lighting recently has become one of the main light sources for various applications. Laser diodes based white lighting is being used in specific cases where lighting of high directionality and power density is desired. Blue laser diode is coupled with yellow phosphor to gain white light in this type of luminaries. Phosphor powder is dispersed in matrix, which is heating due to high laser diode power density. For this reason, phosphor matrix must have good thermal properties. While phosphor in glass, phosphor ceramics and even phosphor crystals are being introduced to solve heating of phosphors problem, in this work ordinary organic matrices used in commercial luminaries were investigated with additionally added boron nitride powder. The main aim of this work was to investigate photoluminescence (PL) and thermal properties of phosphors with boron nitride particles in their holding matrices. Firstly, three different fillers (aluminium, silver and boron nitride (BN) powders) were used to increase thermal conductivity of silicone resin. Three different polymer matrices were also investigated - silicone resin, silicone gasket and acrylic sealant. Samples with YAG:Ce3+ phosphor, BN and silicone resin or silicon gasket were made and their PL and thermal properties were investigated. Silicone gasket and BN was selected as the most suitable holding matrix and samples with sulphoselenide phosphor were prepared. Relative thermal conductivities and PL properties dependencies on phosphor and BN concentrations were measured. In addition, temperature and PL intensity dependency on incident excitation power density of samples were investigated. It was found out, that the commercial silicone gasket with boron nitride powder is suitable composite for holding matrices of phosphors. This filler increases thermal conductivity of samples up to 5 times. The composite does not significantly absorb PL excitation or emission radiation and does not diminish quantum yield. Higher phosphor concentration leads to higher PL intensities due to lower reflection of excitation radiation. The inclusion of boron nitride results in higher reflection of excitation radiation but on the other hand helps to decrease losses based on PL thermal quenching. Therefore, optimal composition of holding matrices must be chosen depending on excitation power density. Temperature of the samples with boron nitride was measured to be lower under the same excitation power densities than for the samples without BN. That means that BN particles contribute to heat dissipation from phosphor particles. In conclusion, holding matrices with BN and silicone gasket are suitable for high power lighting applications where excitation densities do not exceed 300 Wcm-2. |
