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

Abstract

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.

Design of Lanthanide-Doped Colloidal Nanocrystals: Applications as Phosphors, Sensors, and Photocatalysts

“…The low toxicity and significant signal-to-noise ratio of this material make it a potential candidate for in vitro imaging . As has been discussed earlier, our group has prepared a polymer nanocomposite with poly­(vinyl alcohol), and the resulting transparent film had an excellent phosphor property under UV excitation, the digital images of which are shown in Figure …”

“…43 In another study, we have replaced Tb 3+ and Sm 3+ with Mn 2+ ions to produce white-light emission in NaYF 4 nanocrystals. 44 Replacing Ln 3+ ions with transition-metal ions is cheaper because of their abundance. As is clear from the above discussion, most of the studies report the sensitization of visible emission peaks of Ln 3+ ions.…”

“…This results in white-light emission originating from the combination of blue, green, and red emission from Tm 3+ , Tb 3+ , and Sm 3+ ions, respectively (as shown in Figure ). In another study, we have replaced Tb 3+ and Sm 3+ with Mn 2+ ions to produce white-light emission in NaYF 4 nanocrystals . Replacing Ln 3+ ions with transition-metal ions is cheaper because of their abundance.…”

“…Digital image of the Ce 3+ /Tm 3+ /Mn 2+ -doped NaYF 4 /PVA nanocomposite film (A), after bending (B, C and D), and the film under UV light before (E) and after bending (F). Reproduced with permission from ref . Copyright 2017 Wiley.…”

Future prospects of fluoride based upconversion nanoparticles for emerging applications in biomedical and energy harvesting

“…119 The UC properties can also be enhanced with codoping with transition metals. 120 Adusumalli et al 121 used NaYF 4 :Ce 3+ /Tm 3+ /Mn 2+ nanocrystals as an efficient single component phosphor in order to produce intense white light. The Ce 3+ ions were used as the excitation source, and the single blue band emission of Tm 3+ ions was combined with the broadband green-yellow emission of Mn 2+ ions to produce strong white-light emission.…”