Highly Luminescent and Photostable Quantum Dot–Silica Monolith and Its Application to Light-Emitting Diodes

A highly luminescent and photostable quantum dot–silica monolith (QD–SM) substance was prepared by preliminary surface exchange of the QDs and base-catalyzed sol–gel condensation of silica. The SM was heavily doped with 6-mercaptohexanol exchanged QDs up to 12 vol % (26 wt %) without particle aggregation. Propylamine catalyst was important in maintaining the original luminescence of the QDs in the SM during sol–gel condensation. The silica layer was a good barrier against oxygen and moisture, so that the QD–SM maintained its initial luminescence after high-power UV radiation (∼1 W) for 200 h and through the 150 °C LED encapsulant curing process. Green and red light-emitting QD–SMs were applied as color-converting layers on blue LEDs, and the external quantum efficiency reached up to 89% for the green QD–SM and 63% for the red one. A white LED made with a mixture of green and red QDs in the SM, in which the color coordinate was adjusted at (0.23, 0.21) in CIE1931 color space for a backlight application, showed an efficacy of 47 lm/W, the highest value yet reported.