The core/shell-structured upconversion nanophosphors (UCNPs) and Cd-free CuInS2/ZnS quantum dots (QDs) were synthesized via coprecipitation and hot-injection methods, respectively, and they were applied to near infrared (NIR) photodetectors. The β-NaYF4:Yb;Er/β-NaYF4 UCNPs emitted intense visible light peaking at 522, 542, and 656 nm via 2H11/2, 4S3/2, and 4F9/2 → 4I15/2 transitions under excitation with 980 nm NIR light. The core/ shell UCNPs showed 6.4 times higher emission intensity than core UCNPs. Charge carriers can be generated from CuInS2/ZnS QDs in the QD-UCNP mixture due to their broad absorption in the visible spectral region shorter than 600 nm. The photodetector devices were fabricated by spincoating CuInS2/ZnS QDs on a SiO2/Si substrate with patterned gold electrodes followed by spin-coating UCNPs on the QD layer. The fabricated QD-UCNP-bilayer-based device showed a drastically increased photocurrent (128 μA) compared with the QD-layer-based device under 980 nm NIR light illumination. Additionally, the fabricated device showed stable ON-OFF switching properties against on and off NIR light.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics