Thermal management is of critical importance for high power white light-emitting diodes lamps in which blue chip array is combined with yellow phosphors. In this study, the thermal performance of a 100W white LED package on a heat sink with a CCT of 4500K under different phosphor configuration was investigated by a combination of the ray-tracing simulation and computational fluid dynamics simulation. Key simulation results were verified by experiment at first. The simulation results show that the maximum temperature of the model always exists in the phosphor layer. As phosphors are moved away from the LED chips, the maximum temperature of phosphors increases from 120.4°C (200-μm thick conformal phosphor coating) to 160.6°C (in-cup phosphor), and even to 203°C (200-μm thick remote phosphor). It coincides with an analysis of the thermal resistance network of the model, which shows that the major dissipation path for heat generated in the phosphor layer is through the (encapsulant) chips, substrate, heat sink into the air. Among all studied phosphor configurations, the highest junction temperature is 98.3°C, and exists in the model with conformal phosphor coating. It is due to severe absorption of back scattered light by LED chips with phosphor coating.

A special liquid encapsulant and the liquid encapsulation process are developed for enhancing passive cooling for the packaging of monochromatic LED emitters. It was observed that the liquid encapsulation process is superior than the conventional solid silicone encapsulation process in terms of the junction temperature for all the packaged emitters of various wavelengths using the liquid encapsulant. An enhanced reliability in terms of lifetime is thus expected for the emitters encapsulated with the liquid encapsulant. Moreover, an enhanced light output is also demonstrated for the emitters packaged with the liquid encapsulant, which can be attributed to be a result of the improved heat dissipation by convection and conduction in the upward direction through the liquid as well as in the downward direction through the contact area between the liquid and the reflective cup.

Thermal performance of phosphor-based white light-emitting diodes (LEDs) under an input current of 350mA is investigated by finite-element simulation in which the thermal and optical interactions are considered. It is demonstrated that the temperature of the phosphor particles, regardless of phosphor placement, is always higher than the junction temperature. It is concluded that the junction temperature, which characterizes the thermal behavior of monotonic color LED emitters, cannot be used alone for characterizing the thermal behavior of white LED emitters. In fact, the phosphor temperature is critical in determining the lumen performance and reliability of white LED emitters. In addition, the phosphor temperature is effectively reduced by coating the phosphors directly on the chip and maintaining a relatively higher phosphor concentration (above 60 wt.%) in the phosphor-silicone mixture layer.

In this paper, the influence of the die attach adhesive (DAA) layer on the thermal performance of high power light emitting diodes was first investigated by using finite element analysis, and some key results were verified by the experimental data. Effective thermal management of the studied light emitting diode package can be achieved by selecting a DAA material with a proper thermal conductivity and by manipulating the geometry parameters of the DAA layer, such as the DAA area, and the bond-line thickness. The significance of DAA thermal conductivity to heat dissipation was further demonstrated by an analysis of the bottleneck to heat transfer.

A class of red-emitting phosphors Na(5)Ln(MoO4)(4) : Eu3+(Ln = La, Gd and Y) have been synthesized by the sol-gel technique and their luminescent properties have also been investigated under the near-ultraviolet (n-UV) light. The excitation spectra of these phosphors show the strongest absorption at about 395 nm which matches well with the commercially available n-UV-emitting GaN-based LED chip. Their emission spectra show intense red emission at 618 nm due to the D-5(0)-F-7(2) transition of Eu3+. The phosphor Na5Y1-xEux(MoO4)(4) shows the brightest red light among phosphors Na(5)Ln(1-x)Eu(x)(MoO4)(4) as the content of Eu3+ is fixed. In addition, the conditions for synthesis of these phosphors are also optimized, including annealing temperature and concentration of Eu3+ ions. While the Li+ or K+ ions are incorporated into Na5Eu(MoO4)(4) to substitute for Na+ partially, effects on the luminescent properties and structures of phosphors have also been discussed in detail.