Opal Photonic Crystal Enhanced ZnO:Yb³⁺/Er³⁺ Upconversion Luminescence Research

Due to the unique electronic shell structure,the rare earth doped upconversion luminescence material has been found many excellent properties than other type luminescence materials.Upconversion luminescence material is a new material that emits high-energy photons by absorbing two or more low-energy photons.Because of its broad application prospects in solar cells,laser refrigeration,bio-imaging,etc.,the preparation and characterization of upconversion material have received extensive attention.The conventional upconversion luminescence host materials are typically fluorides and oxides.Fluoride-based upconversion materials have been studied a lot,and many achievements have been made.However,some applications are restricted due to poor conductivity,instability and special corrosion of fluorion.ZnO has low phonon energy,high chemical stability and environmental friendliness,which makes it possible to become a preferred matrix host for upconversion luminescence material.In this paper,ZnO is used as the matrix host to carry out research,the specific works have been done for the following:ZnO:Yb3+/Er3+ powders were prepared through simple and easy-controlled hydrothermal method.The phase,structure,morphology and surface elements of the obtained samples were characterized by XRD,SEM,TEM,EDS and UV-Visible spectrophotometry.The performance of upconversion photoluminescence was investigated by fluorescence spectrophotometer.The ZnO:Yb3+/Er3+powder samples generate red emission of 660 nm under the excitation wavelength 980 nm.The effect of Yb3+doped concentration on the upconversion luminescence was studied.The results show that the optimal doped concentration is 20 mol%,and the back energy transfer will lead to fluorescence quenching when the concentration is increased again.In addition,the effect of photonic crystals on the upconversion luminescence of ZnO:Yb3+/Er3+powders was also investigated.The opal photonic crystals(PC)were assembled by vertical deposition of polystyrene microspheres(PS),in which Yb3+/Er3+co-doped ZnO powders were deposited on to the surface of photonic crystal films.The upconversion(UC)emission of ZnO:Yb3+/Er3+on the PC surface was notably enhanced when the UC emission wavelength overlapped with the photonic bandgaps of opals,which is attributed to Bragg reflection of photonic bandgap.The results show that PCs may have potential applications in enhancement of UCPL and optoelectronic devices.