Effect of Cu2+ on the optical properties of zinc oxide-based phosphors prepared in different synthesis conditions

Title : Effect of Cu2+ on the optical properties of zinc oxide-based phosphors prepared in different synthesis conditions

Abstract:

Generally, zinc hydroxides (ZH) and zinc hydroxy carbonates (ZHC) are used for the preparation of ZnO nanoparticles as well as for different functional materials such as thin films, nanocomposites, or inorganic-organic hybrid compounds. Also, due to their strong luminescent characteristics, ZH and ZHC are good candidates for sensing, imaging, drug delivery or optical-electrical display. A green luminescence can be obtained by intercalation of different organic species into Zn(OH)₂ layers while a strong blue emission is observed for Zn₄CO₃(OH)₆×H₂O prepared in hydrothermal conditions. The luminescence of ZH and ZHC is barely studied and is attributed on exciton- exciton collision processes, intrinsic defects, and surface defects, formed during the synthesis stage. The origin of purple-blue emission in zinc hydroxy-carbonate compounds is still not completely clarified and is little studied. On the other hand, the luminescent response of ZH and ZHC as a result of interaction with Cu²⁺ have not been studied. Due to the high defect surface states of ZHC and ZH, Cu²⁺ may easily interact with different active species to form shallow and deep defects fact that can influence the optical properties. In this work, various luminescent zinc hydroxy-carbonate compounds were prepared by precipitation using different precipitating agents such as LiOH, NH₃, Na₂CO₃ and (NH₄)₂CO₃. Based on various investigation techniques (XRD, SEM, FTIR, BET, PL, UV-Vis) the strong connection between Zn²⁺ concentration, pH evolution, morpho-structure and optical properties of ZH, ZHC is discussed. Moreover, understanding the hydrolysis and generation of hydroxy-compounds may provide information on controlling the composition and morphology of ZnO-based nano-materials produced via wet chemical processes. The spherical particles of zinc hydroxy-carbonate compounds ranging between 5 nm and 20 nm, exhibits a strong tendency to form layered or spongy aggregates. BET investigations show that the porosity is distributed either at the surface (ZH) or in the depth of the particles (ZHC) and the specific surface area of samples varies between 15 m²/g and 55 m²/g. The effect of various amounts of Cu²⁺ on optical properties of samples is discussed. Luminescent studies confirm that interaction with Cu²⁺ leads firstly to enhancement and then to quenching of the purple-blue emission of samples while, the energy band gap decreases due to the apparition of new acceptor - donor levels in the optical band gap. A mechanism is proposed to explain the luminescent behaviour of the samples.

Biography:

Laura-Elena Mureşan studied chemistry - physics at Babes Bolyai University, Cluj Napoca, Romania, and after graduating, joined the inorganic research group at the Raluca Ripan Institute for Research in Chemistry, Romania, following in the same time the doctoral studies. She received the PhD degree in 2005 with the thesis entitled, Rare-earth doped luminescent materials.  She currently works at the same institution, as senior researcher with more than 20 years experience in material science. The main research field is focused on the synthesis and characterization of luminescent materials for different applications. The research activity is disseminated in various international journals (77 papers) and 6 patents.