Investigation On Synthesis And Spectral Properties Of Rare-earths Doped Y₂(MoO₄)₃ Phosphors For Blue And Green Upconversion Emissions

Upconversion luminescence materials are one kind of light-emitting materials with the feature that emitting short wavelength photons while excited with long wavelength photons. Most of them are rare earths doped materials such as Er3+/Yb3+ codoped Y2O3 and NaYF4, etc. These materials can emit different color visible lights. Over the past several decades, rare earths doped upconversion luminescence materials have been intensively studied due to their potential applications in many fields, such as three-dimensional displays, optical data storage, medical diagnostics, sensors, laser and optical amplifiers. In this thesis, Er3+/Yb3+codoped Y2(MoO4)3 phosphors were synthesized via co-precipitation method and solid-state reaction method, respectively. In addition, Tm3+/Yb3+ codoped Y2(MoO4)3 phosphors were synthesized via solid-state reaction method. Their upconverting properties were investigated. The obtained results are described as follows:Er3+/Yb3+ codoped Y2(MoO4)3 nanophosphors were synthesized via co-precipitation method. The structural and morphological of the samples were investigated. It was found that the two-photon process is responsible for both red and green upconversion emissions in the samples doped with both low and high Yb3+ concentrations. The dependence of upconversion emission intensity ratio of 2H11/2â†'4I15/2/4S3/2â†'4I15/2 on LD working current was studied. The ratio changes slightly with the LD working current in the sample doped with low Yb3+ concentration, whereas it changes significantly with the LD working current in the sample doped with high Yb3+ concentration. Apart from the rate equation model, an empirical formula for describing the dependence of upconversion emission intensity on the Yb3+ doping concentration was obtained, and the empirical formula fits well to the experimental data in the studied system. Besides, Er3+/Yb3+ codoped Y2 (MoO4)3 bulk phosphors were synthesized via solid-state reaction method. The effects of LD pump current and dopant concentrations on upconversion luminescence were studied. The results of nanophosphor and bulk phosphor were compared. Tm3+/Yb3+ codoped Y2(MoO4)3 bulk phosphors were synthesized via solid-state reaction method. Dependence of upconversion emission intensity on LD working current and dopant concentration was investigated. It was found that the three-photon processes are responsible for both blue and red upconversion emissions, and two-photon process is responsible for infrared upconversion emission in all the samples doped with various Tm3+ and Yb3+ concentrations. It was also found that the upconversion luminescence intensity changes strongly as Tm3+ concentration increases and softly as Yb3+ concentration increases.