Luminescent composite material fabricated from carbon dots and red phosphors for application to UV-LED chips and metal ion detection

Abstract

Carbon dots with a size of 5 nm were synthesized through hydrothermal synthesis by recycling discarded coffee powder. In the Raman signal, the typical D (1364 cm−1) and G (1563 cm−1) bands of Sp2 carbon were detected, and when excited at 324 nm, a blue, wide-range emission spectrum signal was detected. The synthesized carbon dots were mixed with a solution containing 10 ppm of Pb, Cr, and Cd to be used in the field of detecting metal ions in a solution state. Carbon dots that reacted with metal ions lost their unique blue luminescent color and showed that they could be used as metal ion detection sensors. In addition, spherical particle CaWO4:Eu3+ phosphor powder was synthesized and prepared by coprecipitation at room temperature. The synthesized phosphor had a tetragonal structure, and a strong signal from the (112) plane, the main peak, was detected in the XRD pattern, showing excellent crystallinity. When excited at 267 nm, a strong red emission signal of 613 nm was detected, and when the synthesized carbon dots were impregnated and made into a composite, an emission spectrum was observed in a wide range from blue to red, showing white color. This composite was mixed with PDMS to make a flexible sheet and applied to a UV-LED chip, suggesting that it could be used as a white light-emitting device.