Type‐II CdSe/ZnO Core/Shell Nanorods: Nanoheterostructures with A Tunable Dual Emission in Visible and Near‐Infrared Spectral Ranges

• Published in: Advanced functional materials 2024-04, Vol.34 (16), p.n/a
• Main Authors: Haque, Anamul, Zechel, Filip, Vretenár, Viliam, Roy, Mrinmoy, Sýkora, Milan
• Format: Article
• Language: English
• Subjects: Carrier recombination; CdSe/ZnO; colloidal synthesis; core‐shell; Heterostructures; Medical imaging; nanocrystals; nanoheterostructures; Nanorods; Near infrared radiation; Optoelectronics; Photoluminescence; Quantum confinement; type‐II; Zinc oxide
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202305296

A synthesis and characterization of luminescent nano‐heterostructures consisting of CdSe nanorod (NR) cores and a ZnO shell with up to three monolayers of ZnO is reported. The core/shell heterostructures show a tunable, dual photoluminescence (PL) in visible and Near Infrared (NIR) spectral ranges. Upon shelling the visible PL band attributed to the carrier recombination within the CdSe core shifts to lower energy by ≈0.05 to 0.15 eV relative to the bare CdSe NRs, due to a reduced quantum confinement. A NIR band, observed ≈0.4 – 0.5 eV below the PL energy of the CdSe core, is attributed to a type‐II carrier recombination across the CdSe/ZnO interface. The total PL quantum yield (PLQY) in the brightest heterostructures reaches ≈20%, increasing ≈100‐fold over the PLQY of the corresponding bare CdSe NRs. The average lifetimes of the visible PL in some heterostructures exceeds 100 ns, compared to ≈5 ns lifetime typical for bare CdSe NRs. The average PL lifetimes attributed to the type‐II charge separated states exceed one microsecond. Strong NIR PL, tunable in the 800–900 nm spectral range and the long‐lived charge separated state make the CdSe/ZnO core‐shell NRs appealing materials for exploitation in applications such as bioimaging, photocatalysis and optoelectronics. Overcoating of CdSe nanorods with a ZnO shell leads to observation of dual visible and near‐infrared photoluminescence with a dramatic enhancement in quantum yield and the lifetime of the excited state. The visible emission is a result of the electron‐hole recombination within the CdSe core, while the NIR emission is a result of type‐II carrier recombination across the CdSe/ZnO interface, resulting from an electron delocalization.