Investigation of photoluminescence and thermal effect of phosphor films used in phosphor-converted white LEDs

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By using a blue light source converted by phosphors to obtain white light emission, phosphor-converted white light emitting diodes (pc-white LEDs) are becoming as one of substitutes of traditional general lighting sources due to their advantages in energy saving, environment-friendliness, color controllability and long lifetime. Within pc-white LEDs, the phosphor films consisting of inorganic phosphor powders and silicone have a great effect on the luminous efficacy, color stability and color rendering properties of the LEDs. Additionally, as being close to LED chips, the phosphor film always suffers a high temperature when the LED operates. Thus, the photoluminescence and thermal effect of phosphor films become the essential research topics to identify the resulting failure mechanisms in LEDs. This study selected five widely used inorganic phosphor powers with Garnets, Silicates, Aluminates and Nitrides bases mixed with silicone to prepare the phosphor films. Then, with a 450nm InGaN blue chip as an excitation source, a thermal-controllable platform was installed in an integrating sphere to measure the thermal transient photoluminescence properties of these above prepared phosphor films. Finally, optical simulations using the LightTools software were conducted to predict the spectral power distributions (SPDs) of the pc-white LEDs with selected phosphors films. The simulated SPDs are in reasonable agreement with those measured from experiments. This implies the proposed simulation method can be a useful tool instead of physical experiments in the phosphor design for pc-white LEDs.