Physical Limitations of Phosphor layer thickness and concentration for White LEDs

Abstract

Increasing phosphor layer thickness and concentration can enhance the lumen flux of white LED (W-LED). In this work, we found that increasing the phosphor layer thickness and concentration can increase its temperature, and there is also a maximum thickness and concentration beyond which their increase will not lead to lumen increase, but only temperature increase. Higher thickness and higher concentration also results in warm light instead of White light. The maximum thickness and concentration are found to be limited by the scattering of light rays with higher % decrease of blue light rays than the yellow light rays. The results obtained in this work can also be used to compute the temperature and thermo-mechanical stress distribution of an encapsulated LED, demonstrating its usefulness to the design of encapsulated LED packages. Simulation software like ANSYS and TracePro are used extensively to verify the root cause mechanisms.

Experimental investigation and empirical modelling of thermal and drive current effect on optical performance of commercial LEDs

“…The work also helps to understand the physics of degradation involved as a factor of humidity, temperature and current of LEDs. An extension of this work is found in Tan et al 12 which deals with variations in the phosphor layer thickness and analysing the changes in junction temperature and thus its effect on lumen output. The study shows that there exists a maximum thickness of the phosphor layer after which the lumen output ceases to increase and only temperature increases which further results in less lumen output.…”

Remote phosphor-based extended white light source pumped by single blue LED for efficient lighting

“…In this method, a slight improvement in the luminance was observed but quenching effect was not removed completely or signi cantly [20][21][22]. The back re ection of blue component was reduced due to high blue irradiance absorption but backward uorescence is still an issue for high non-radiative inside the LED junction which affects the life time of high brightness LED [13,[22][23][24]. Therefore, multiple small blue LEDs (MSB-LED) are being used to replace high brightness LED and it is currently a successful approach for higher e cacy illumination [25][26].…”

“…YAG: Ce +3 is an inorganic rare earth material with high quantum e ciency, long life-time and good color parameters [8,[11][12]. It has been reported that YAG: Ce +3 shows drop in emission intensity with the different temperatures generated from non-radiative transition of LED [13][14][15][16]. Both, the backward uorescence and the blue photon back-re ection from phosphor layer are responsible for high nonradiative relaxation rates inside the LED junction which leads high temperature generation at LED-phosphor interface [16][17][18][19].…”

Luminous Performances Characterization of YAG: Ce3+ Phosphor/Silicone Composites Using Both Reflective and Transmissive Laser Excitations

“…The results showed that with the increase in the YAG concentration, the transmittance of phosphor/silicone decreased and the luminous efficiency increased, while the peak wavelength and full width at half maximum (FWHM) of blue and yellow lights were basically unchanged. Through TracePro simulation, Tan et al [7] revealed that with the increase of phosphor particles in the phosphor/silicone composite, the luminous flux increased first, and then decrease. Moreover, through ASAP simulation, Sommer et al [8] found that the phosphor concentration in the phosphor/silicone composite will affect its spatial color distribution.…”