Quantum dot phosphors free from hazardous elements: Current status and prospects for established materials and new ZnTe-based alloys

Television broadcasts are moving to a digital video format based on ultra-high-definition (UHD). In addition to high resolution, such UHD displays require a wide color gamut. Quantum dots (QDs) have narrow and color-tunable emission making these unique light sources for achieving a wide color gamut. Most progress in QDs has been made based on cadmium-containing materials, as represented by CdSe. These systems have excellent performance in terms of their narrow-band emission and high emission quantum yield; however, the toxicity of cadmium represents a barrier to practical applications of QD displays. Over the last decade, considerable efforts have been made to develop QDs that do not contain cadmium. Some established alternative materials include InP, CuInS₂, and lead halide perovskites. In addition, ZnTe-based alloy QDs have recently been proposed as promising green and red phosphors. Narrow-band and green emission (30 nm of full-width at half-maximum at a wavelength of 535 nm) has also been reported for Zn (Te, Se) alloy QDs. In this review article, we give a brief overview of progress in established cadmium-free QDs and describe the current status and future challenges of new cadmium-free QDs, ZnTe-based alloy QDs.