| With the rapid developments of upconversion luminescence research, many new applications using upconversion luminescent materials have been emerged, such as anti-counterfeiting, solar infrared capture, vivo biological imaging, etc. However, high requirements on stability and multicolor luminous performance of the upconversion luminescence materials are desired for the new applications. For example, the materials used in the solar infrared capture application should be stable in a variety of harsh environments outside for more than two decades. The vivo biological imaging requires high efficient red or near infrared light in biological body. In addition, the upconversion materials should be fine mono-disperse particles with quasi-spherical shape, in order to ensure the uniformity of the coating of solar cells and the liquidity in the human blood. The traditional fluoride conversion materials cannot meet all of the above requirements. While oxide and oxysulfide have been widely used in the fields of illumination and display due to the high upconversion efficiency and stable physicochemical properties. In recent years, they also play important roles in the fields of biomedical and solar cells. In this work, the oxide and oxysulfide upconversion materials are studied in details and summarized below:1. The synthesis of high crystallinity, spherical and monodisperse Y2O2S matrix materials.The Y2O2S samples were synthesized by a novel two-step method of high temperature solid-state reaction and subsequent colloidal processing. The obtained product shows single hexagonal phase and monodispersed spherical morphology with a mean particle size of 120±34nm. And the particles exhibit excellent dispersibility in ethanol solution. The reasons were also discussed in detail in the paper.2. The multicolor light characteristics of Y2O3:Er, and Y2O3:Yb, Er upconversion luminescent materials under 1550 nm excitation were explored, and were compared to that of Y2O3:Er, and Y2O3:Yb, Er under 980 nm excitation.1) The Y2O3:Yb, Er phosphors were prepared by solid-state reaction. This study explores a new method to achieve highly efficient red upconversion luminescence by using the Y2O3:Yb, Er material pumping with a 1550 nm laser diode. The upconversion luminescence brightness of Y2O3:Yb, Er under 1550 nm excitation is comparable to that of Y2O3:Yb, Er under 980 nm excitation by using the same power density. In addition, Y2O3:Yb, Er under 1550nm excitation exhibits excellent superior excitation characteristics under low excitation power and presents a saturation effect under higher power excitation. The upconversion luminescence intensity of Y2O3:Yb, Er under 1550 nm and 980 nm excitation has been analyzed quantitatively. The results show that the Y2O3:Yb, Er under 1550 nm excitation exhibits the high efficient red upconversion luminescence. By increasing the 1550 nm pumping power, Y2O3:Yb, Er presents much better color purity and color stability.2) The Y2O3:Er and Y2O3:Yb, Er nanoparticles were synthesized by homogeneous precipitation method. The obtained product shows subspherical shape with a mean particle size of 120±34 nm. The photoluminescence spectra indicate that the Y2O3:Er presents strong green emission, while Y2O3:Yb, Er shows relatively pure red emission under 980 nm excitation. But the green emission of Y2O3:Er is significant decreased and the red emission enhanced obviously, while Y2O3:Yb, Er emerges a single red emission. Due to energy transfer of Er3+â†'Yb3+â†'Er3+effectively enhances the intensity of red emission. In addition, pure red emission color can be further improved by appropriate increasing excitation power and Er3+ion doping concentration.Y2O3:Er and Y2O3:Yb, Er under 1550 nm excitation have an relatively strong NIR radiation around 980 nm, which is favorable for biomedical and near infrared captured solar energy applications. |
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