Synthesis of Er- and Yb-doped gadolinium oxide polymorphs and influence of their structures on upconversion properties

Abstract

Nanocrystalline Gd₂O₃ products doped with Er³⁺ and Yb³⁺ cations were synthesized by combustion method. We showed that the temperature of combustion can be tuned by using different types of organic fuels within reaction mixture. The combustion process is performed at lower temperature in the presence of urea as an organic fuel leading to pure cubic Gd₂O₃:Er,Yb phase, on the other hand higher combustion temperature, yielding pure monoclinic Gd₂O₃:Er,Yb polymorph is achieved in the mixture of urea and b-alanine. Effective doping of Er³⁺ and Yb³⁺ cations within Gd₂O₃ were confirmed by XRD analysis. Both polymorphs show upconversion in green and red areas and possess strong dependence of fluorescence intensity ratios (I₅₂₅/I₅₄₉ or I₅₂₅/I₅₆₀ for monoclinic and cubic polymorphs, respectively) on temperature. This indicates that both phases can be applied for the temperature sensor devices based on upconversion intensity ratio changes.