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Structural metastability and quantum confinement in Zn1- xCoxO nanoparticles

Abstract: This paper investigates the electronic structure of wurtzite (W) and rock-salt (RS) Zn1?xCoxO nanoparticles (NPs) by means of optical measurements under pressure (up to 25 GPa), X-ray absorption, and transmission electron microscopy. W-NPs were chemically synthesized at ambient conditions and RS-NPs were obtained by pressure-induced transformation of W-NPs. In contrast to the abrupt phase transition in W?Zn1?xCoxO as thin film or single crystal, occurring sharply at about 9 GPa, spectroscopic signatures of tetrahedral Co2+ are observed in NPs from ambient pressure to about 17 GPa. Above this pressure, several changes in the absorption spectrum reveal a gradual and irreversible W-to-RS phase transition: (i) the fundamental band-to-band edge shifts to higher photon energies; (ii) the charge-transfer absorption band virtually disappears (or overlaps the fundamental edge); and (iii) the intensity of the crystal-field absorption peaks of Co2+ around 2 eV decreases by an order of magnitude and shifts to 2.5 eV. After incomplete phase transition pressure cycles, the absorption edge of nontransformed W-NPs at ambient pressure exhibits a blue shift of 0.22 eV. This extra shift is interpreted in terms of quantum confinement effects. The observed gradual phase transition and metastability are related to the NP size distribution: the larger the NP, the lower the W-to-RS transition pressure

 Autoría: Almonacid G., Martín-Rodríguez R., Renero-Lecuna C., Pellicer-Porres J., Agouram S., Valiente R., González J., Rodríguez F., Nataf L., Gamelin D., Segura A.,

 Fuente: Nano Letters, 2016, 16(8), 5204-5212

Editorial: American Chemical Society

 Fecha de publicación: 01/07/2016

Nº de páginas: 9

Tipo de publicación: Artículo de Revista

 DOI: 10.1021/acs.nanolett.6b02230

ISSN: 1530-6984,1530-6992

Proyecto español: MAT2015-69508-P ; MAT2012-38664-C02-01/02

Autores/as

ALMONACID CABALLER, GLORIA

CARLOS RENERO LECUNA

PELLICER PORRES, JULIO

AGOURAM, SAID

LUCIE NATAF

GAMELIN, DANIEL R.

ALFREDO SEGURA GARCIA DEL RIO