Photoluminescence in ZnO:Co²⁺ (0.01%–5%) Nanoparticles, Nanowires, Thin Films, and Single Crystals as a Function of Pressure and Temperature: Exploring Electron–Phonon Interactions

Abstract

This work investigates the electronic structure and photoluminescence properties of Co2+-doped ZnO and their pressure and temperature dependences through high-resolution absorption and emission spectroscopy as a function of Co2+ concentration and their structural conformations as a single crystal, thin film, nanowire, and nanoparticle. Absorption and emission spectra of diluted ZnO:Co2+ (0.01 mol %) can be related to the 4T1(P) → 4A2(F) transition of CoO4 (T d ), contrary to MgAl2O4:Co2+ and ZnAl2O4:Co2+ spinels in which the red emission is ascribed to the 2E(G) → 4A2(F) transition. We show that the low-temperature emission band consists of a 4T1(P) zero-phonon line and a phonon-sideband, which is described in terms of the phonon density of states within an intermediate coupling scheme (S = 1.35) involving all ZnO lattice phonons. Increasing pressure to the sample shifts the zero-phonon line to higher energy as expected for the 4T1(P) state upon compression. The low-temperature emission quenches above 5 GPa as a consequence of the pressure-induced wurtzite to rock-salt structural phase transition, yielding a change of Co2+ coordination from 4-fold T d to 6-fold O h . We also show that the optical properties of ZnO:Co2+ (T d ) are similar, independent of the structural conformation of the host and the cobalt concentration. The Co2+ enters into regular Zn2+ sites in low concentration systems (less than 5% of Co2+), although some slight shifts and peak broadening appear as the dimensionality of the sample decreases. These structural effects on the optical spectra are also supported by Raman spectroscopy.

Dopant-Controlled Selenization in Pd Nanocrystals: The Triggered Kirkendall Effect

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 9 However, contrasting results were obtained when these doped Pd(0) nanostructures were treated for selenization using a similar method to that followed for the undoped metal. It was observed that hollow cubic shaped Ag doped Pd 17 (Table S1). Hence, it can be speculated that following selenization of the doped metal, the shape changes but the phase of the final structure is the same as that of the undoped structure.…”

“…Many studies have been conducted on the doping of a wide variety of inorganic dopants into various metal oxide and semiconductor host nanomaterials and the properties of the newly formed materials have been well studied. 1-9, [14][15][16][17][18][19][20][21][22][23][24][25][26][27] Optically active dopants can create new electronic states and can assist in the creation of new optical centers to produce different colored emissions. 1-8, [14][15][16][17][28][29][30] Similarly, magnetic dopants can even introduce magnetic properties in non-magnetic hosts.…”

“…1-9, [14][15][16][17][18][19][20][21][22][23][24][25][26][27] Optically active dopants can create new electronic states and can assist in the creation of new optical centers to produce different colored emissions. 1-8, [14][15][16][17][28][29][30] Similarly, magnetic dopants can even introduce magnetic properties in non-magnetic hosts. 9,[18][19][20][21][22] Recently, it has been reported that dopants can influence the charge carrier density of the host materials and thus generate metallic type localized surface plasmon resonance in semiconductor nanostructures.…”

Effect of Size, Shape, and Composition on the Interaction of Different Nanomaterials with HeLa Cells

“…TiO 2 and ZnO nanoparticles (Z-COTE®) were commercial (BASF Chemical Company). ZnO:Co 2+ nanowires were synthesised in-house [34][35][36]. Chemically exfoliated graphene oxide (GO) was purchased commercially (Graphenea, Spain).…”

Structural Metastability and Quantum Confinement in Zn1–xCoxO Nanoparticles

“…The way these absorption bands contribute to photovoltaic and photoconductivity effects is a critical issue for the above referred applications and has been the object of several studies. 18,33−36 High-pressure techniques are well suited to investigate the electronic structure of semiconductor materials 37 already been used to study the electronic structure of Zn 1−x Co x O NPs, 38 thin films, 35,39−41 and single crystals. 4,42 High pressure was also crucial to elucidate electronic structure effects related to quantum confinement in quantum dots.…”