Ce3+-Sensitized Tm3+/Mn2+-Doped NaYF4 Colloidal Nanocrystals: Intense Cool White Light from a Phosphor-Coated UV LED

Colloidal NaYF4: Ce3+/Tm3+/Mn2+ nanocrystals found to be an efficient single component phosphor to produce intense white light. The use of Mn2+ ions instead of green-and red-emitting Ln(3+) ions is interesting as the later are expensive and less abundant. The single band blue emission of Tm3+ ions was combined with the broadband green-yellow emission of Mn2+ ions to produce strong white light emission using Ce3+ ions as excitation source. Interestingly, there is hardly any re-absorption of the blue emission by Mn2+ ions and the spectrum matches the commercial Ce3+-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 (Mn2+) ions was tuned the correlated color temperature (CCT) values varied between cool white light and daylight region.