I am looking for the structure of the host and the dopants. As we usually use Ce3+ and Eu2+ for both the colours, can we have a host with necessary added other dopants that can generate both. This is for warm light LED approach.
Dear Mairaba,
Over the years, Oxynitrides and Nitrides doped with Ce3+ or Eu2+ are emerged as a broad blue, green and red emitting phosphor for White light emitting diodes. These materials have broad excitation suitable for InGaN chip. Commercially, YAG:Ce3+ is used as phosphor for WLED. However today, there is some red component (phosphor) is added to YAG:Ce3+ for INGaN LED.
I have attached one review paper on Oxynitride. Hope this will help you.
Dear Meiraba, The stillwellite family are very well known compounds to accept all the rare earth dopants, out of which Eu2+, Eu3+, and Tb3+ that are proven to emit blue, red and green in these compounds. The stillwellite family is described by the general formula (Ln+3,M+2)B(Si,Ge,Al,P)(O,OH,F)5.0. However, preparing these compounds is usually done at relatively elevating temperatures and one might need to control the pressure and the atmosphere as well. Hope this will help ...
Dear Hassan,
Eu3+ and Tb3+ have forbidden transitions and therefore they have weak absorption in the blue region where InGaN chip emits. Also they have sharp emission one in red region (Eu3+) and other one in Green region (Tb3+) which is of no use for WLED (i.e sharp emission of Eu3+ and Tb3+). Also Eu3+ has sharp excitation peak at 394 nm while Tb3+ has peaks in shorter UV region. How can you say these two rare earth can be used for WLED?????
Now a days there are number of reports publishing claiming Eu3+, Dy3+ and Tb3+ for WLED. This is impossible to do. I want to tell the researchers working with Eu3+, Tb3+ and Dy3+, that these three rare earth with 3+ state is of no use to WLED. Frankly speaking all these papers should be thrown to dustbin because they are misleading to students.
To get broad emission and excitation you should try Ce3+ and Eu2+ and other rare earths or transition metals which have allowed transition.
best wishes
Dear Rupesh, In order to overcome the weak absorption of some of the rare earth ions or any dopant in general, you have to co-dope your host with another dopant that can absorb well in the desired region and transfer all or part of its energy to the other luminescent center to improve its emission within the region of interest. Also as I mentioned before, the borosilicate family can accomodate the Eu2+ which happen to emit in the blue when introduced into this family. Finaly, when you try to design a new material with a specific property, you have to think out of the box ... Best of luck
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