Dear Ishant

In order to fabricating white LED using red green and blue phosphors, you require UV (365-385 nm) or n-UV LED (400-410 nm) coated with three phosphors emitting in the blue, green and red region. All the three materials should have excitation in the region where the LED is emitting and emission in the blue, green and red region. It is very important to optimize each phosphor so as to achieve highest efficiency when mixed with the other two phosphor. Also to optimize all three colors simultaneously so as to achieve good color-coordinates and color rendering index (CRI) is not easy.

The main drawback or bottleneck with UV or n-UV LEDs are the cost.

At present the cost the UV is around some 2-3 $ and also for 410 nm it is 1-2 $ each. Whereas the cost of InGaN blue LED chip (~ 460 nm) is around 0.1-0.25 $ in the market, which is commercially used for White LED application when coated with YAG:Ce phosphor.

The best and easiest way to fabricate white LED with good CRI and color coordinate is to use blue LED InGaN chip with Y3Al5O12:Ce3+ phosphor. To further improve the CRI and color coordinate you may add Eu2+ doped Nitrides, Oxynitrides, etc as red emitting luminescent materials.

Thanks a lot for your kind explanation Mr Rupesh Talewar .

Can you please explain a little bit more how the three color phosphor coating is done ? Is there is homogeneous mixing done first and then by some deposition method like electron beam or CVD etc method coating is done or layer by layer coating is done for different phosphors i.e first red phosphor then blue and last green phosphor ?

Dear Ishant

As per my knowledge and what I have seen in one of the LED fabrication unit in India, where they use Blue LED chip coated with YAG:Ce3+ and some Eu2+ doped nitride. They use mixture (in optimize ratio) of YAG:Ce3+ and Eu2+ phosphor dispersed in some resin or epoxy then they simply coat this on the chip. Same procedure may be applied for UV or n-UV LED chips with three different phosphors emitting in red, green and blue. You have to do this on trial and error basis to optimize the ration between the phosphors.

If you have any white LED try to open it, try to see the how phosphors are coated on the chip.

Thanks a lot for Mr Talewar your explanations.

I believe that in our school days when ever we mix all colors we used to get a white light. However, of all the colors if we can mix Blue, Green and Red of equal proportion then you will get white light. As per research terminology equal proportion does not mean amount it means intensity which will allow the spectra to start somewhere near blue (390 nm) and falls down in red (700 nm). Thus the spectra is said to emit complete white light. It can be achieved by doping, codoping or mixing different materials which emit in Blue, Green and Red region

Thanks for your explanation Mr Rajesh

The different phosphors are made in form of triad dots such that after absorbing the UV radiation will release either red, or green or blue. The eye will integrate the three colors and perceive it in white color.

The white light can also built by blue light complemented by yellow light to form white light. So, if the light is originally blue then part of it will be passed and the other part will be converted to yellow by a yellow phosphor.

Another solution for forming white light is not using phosphor at all but using triad LEDS where the LEDS emits blue green and red light.

The most feasible solution is to use the complementary colors blue+ yellow to form white.

Best wishes