Ce 3+ -Sensitized Tm 3+ /Mn 2+ -Doped NaYF 4 Colloidal Nanocrystals: Intense Cool White Light from a Phosphor-Coated UV LED

Colloidal NaYF :Ce /Tm /Mn nanocrystals found to be an efficient single component phosphor to produce intense white light. The use of Mn ions instead of green- and red-emitting Ln ions is interesting as the later are expensive and less abundant. The single band blue emission of Tm ions was combined with the broadband green-yellow emission of Mn ions to produce strong white light emission using Ce ions as excitation source. Interestingly, there is hardly any re-absorption of the blue emission by Mn ions and the spectrum matches the commercial Ce -doped yttrium aluminium garnet (YAG) phosphor coated over a blue LED. In addition, we have successfully incorporated the colloidal nanocrystals into a polymer matrix to make a nanocomposite as well as transparent films without altering the optical properties of the nanocrystals. The colloidal nanocomposite was coated over a UV LED to fabricate white LEDs. Finally, when the concentration of the dopant (Mn ) ions was tuned the correlated color temperature (CCT) values varied between cool white light and daylight region.