Annealing temperature and environment effects on ZnO nanocrystals embedded in SiO2: a photoluminescence and TEM study

Abstract

We report on efficient ZnO nanocrystal (ZnO-NC) emission in the near-UV region. We show that luminescence from ZnO nanocrystals embedded in a SiO2 matrix can vary significantly as a function of the annealing temperature from 450°C to 700°C. We manage to correlate the emission of the ZnO nanocrystals embedded in SiO2 thin films with transmission electron microscopy images in order to optimize the fabrication process. Emission can be explained using two main contributions, near-band-edge emission (UV range) and defect-related emissions (visible). Both contributions over 500°C are found to be size dependent in intensity due to a decrease of the absorption cross section. For the smallest-size nanocrystals, UV emission can only be accounted for using a blueshifted UV contribution as compared to the ZnO band gap. In order to further optimize the emission properties, we have studied different annealing atmospheres under oxygen and under argon gas. We conclude that a softer annealing temperature at 450°C but with longer annealing time under oxygen is the most preferable scenario in order to improve near-UV emission of the ZnO nanocrystals embedded in an SiO2 matrix.

Study of energy transfer mechanism from ZnO nanocrystals to Eu3+ ions

“…In this article, we present in detail the contribution of the various de-excitation processes of excited ZnO-nc embedded in SiO 2 matrix in the energy transfer process from ZnO-nc to Eu 3+ ions and we suggest a suitable mechanism for the energy transfer process. This is an extension of our earlier work [ 18 ], where the various de-excitation processes of the ZnO-nc in SiO 2 were identified as being made of seven contributions. In this work, the low-cost sol-gel process was used to make the samples due to the flexibility of controlling the material composition and the structures of the thin film.…”

“…For the Eu 3+ :SiO 2 sample, the molar ratio of Eu 3+ :Si was kept the same as that in the Eu 3+ 0.12 :(ZnO-nc:SiO 2 ) sample. The preparation method used for the above samples is similar to that described in our previous publication [ 18 ]. In the first step of the three-step process, the precursor, the solvent and the catalyst were mixed to create the sol.…”

Energy Transfer Efficiency from ZnO-Nanocrystals to Eu3+ Ions Embedded in SiO2 Film for Emission at 614 nm

“…Finally, the samples were soft baked for 5 m at 100 °C and subsequently annealed at 450 °C in an O 2 environment for 60 s using the Rapid Thermal Annealing (RTP) process. The steps of fabrication are exactly same as those reported in our previous publications [ 9 , 10 ], and the exact same samples used in our previous study of the steady-state PL emission from ZnO-nc and Eu 3+ ions were also used for this work [ 9 ]. The formation of ZnO-nc embedded in an SiO 2 matrix using this sol-gel recipe has been studied in detail in our group’s earlier publication [ 10 ], wherein the TEM images of the samples were analyzed to confirm the formation of ZnO-nc.…”

“…This article is a direct continuation of our earlier work [ 9 ], in which the steady-state PL emission from ZnO-nc was studied to elucidate the contribution of seven ZnO-nc emission centers in the energy transfer process to Eu 3+ ions. These seven emission centers of the ZnO-nc in SiO 2 , centered at 360, 378, 396, 417, 450, 500, and 575 nm [ 10 ], were identified as band-edge emissions from the smallest ZnO-nc, which possibly experiences some quantum confinement effect (QC) [ 11 ], excitonic emission (EE) [ 12 , 13 ], and five different defect state emissions, namely Zn defect (Zn i to V Zn ) [ 14 ], oxygen interstitial defect (O i ) [ 15 , 16 ], and oxygen vacancy defects (V o , VȮ, VӦ) [ 14 , 17 , 18 ], respectively. In this work, we study the contribution of energy transfer from various ZnO-nc emission centers to Eu 3+ ions based on TRPL measurements.…”

Novel photoluminescence properties and enhanced photocatalytic activities for V2O5-loaded ZnO nanorods

“…5 The ZnO nanostructure is an important semiconductor with a direct bandgap of 3.34 eV, and the primary motivator of ZnO research is its great potential for a variety of practical applications, such as in LEDs, 6 solar cells, 7 nanogenerators, 8 transistors, 9 sensors, 10 catalysts, 11 etc. In many literature studies, a variety of strategies, such as doping, 14,15 thermal annealing, [16][17][18] plasma treatment, 19,20 and constructing heteronanostructures, 21,22 have been developed. For example, visible-light-driven photocatalytic properties have been observed in ZnO/ZnFe 2 O 4 core/shell nanocable arrays.…”