White LED question

[Landrew]

I understand from the literature that the white LED was made possible only by the advent of the bright blue LED in 1993, which could be mixed with other colors to make a white light.  Apparently the blue LED had existed for years, but it was so dim that the only significant application for it was as a headlight indicator on a VW Rabbit.


But then, I was reading that many LEDs in the earlier days (since the seventies) were made using phosphors, energized from a layer below.  (Nowadays of course they are mostly powered from a white LED die, which emits white light directly from the substrate).


My puzzlement is that if white phosphors already existed decades ago (as in B&W TVs) then why couldn't white LEDs have been available decades ago?

[Heinz Doofenshmirtz]

Probably limitations in the manufacturing technology.  My understanding is that as LED's have improved in terms of output and efficiency, it's because of improvements in the thinning of the superstrate and substrate materials (less current conducted) and density in the reaction sites between them (more light generated).  That's just my educated guess, though... I don't know a whole lot about the actual physics of LED's themselves.

[Steinar]

Err... Bombarding a layer of phosphorus with an electron beam is not quite the same as applying a small current through a p-n junction. Personally, I suspect it has very much to do with practicality, power consumption and price, though I have absolutely no facts to back it up.

[Landrew]

Err... Bombarding a layer of phosphorus with an electron beam is not quite the same as applying a small current through a p-n junction. Personally, I suspect it has very much to do with practicality, power consumption and price, though I have absolutely no facts to back it up.

My understanding is that phosphors can be energized several different ways, of which an electron beam is only one.  I believe LEDs do this by bombarding the phosphor with ultraviolet light.

[Heinz Doofenshmirtz]

For all our edification:

http://en.wikipedia.org/wiki/Light_emitting_diode

Haven't read the whole thing myself, but I plan to soon.

[Landrew]

For all our edification:

http://en.wikipedia.org/wiki/Light_emitting_diode

Haven't read the whole thing myself, but I plan to soon.

It was my reading of that WP article that partly inspired my question.