Surface-Enabled Energy Transfer in Ga2O3–CdSe/CdS Nanocrystal Composite Films: Tunable All-Inorganic Rare Earth Element-Free White-Emitting Phosphor

Abstract

Development of inorganic phosphors capable of generating white light in a homogeneous and reproducible fashion without the use of rare earth elements can lead to an efficient, long-lasting, and sustainable solid state lighting. The design of such phosphors requires that different inorganic components emitting in complementary spectral ranges are electronically coupled to avoid the challenges associated with a multicomponent approach, such as inhomogeneity, poor chromaticity control, and low color rendering index. Here we demonstrate coupling between electronically excited blue-emitting Ga2O3 and orange-red-emitting CdSe/CdS core/shell nanocrystals by surface-enabled Förster resonance energy transfer. This energy transfer process is evident from quenching of Ga2O3 (donor) and an enhancement of CdSe/CdS (acceptor) nanocrystal emission and is further confirmed through the diminished lifetime of Ga2O3 and significantly extended lifetime of CdSe/CdS nanocrystals in the composite films. Controlling the energy transfer efficiency by adjusting the separation and distribution of codeposited CdSe/CdS and Ga2O3 nanocrystals allows for tuning of the emission color. White light is reproducibly generated for [CdSe/CdS]:[Ga2O3] ≈ 0.5 by tuning energy transfer efficiency to be ca. 25% using 4.5 ± 0.3 nm Ga2O3 and 6.4 ± 0.3 nm CdSe/CdS nanocrystals. The main goal of this work is to quantitatively explore the energy transfer coupling between heterogeneous nanocrystals having complementary optical properties, anchored without the application of organic linkers. These broadly relevant results are applied to demonstrate a path to all-inorganic rare earth element-free nanocrystal phosphors for potential application in white light-emitting diodes and other light-emitting devices.