Papers by Author: Yan Dong

Abstract: Hexagonal (β)-phase NaYF₄:Yb³⁺, Er³⁺ upconversion nanoparticles (UCNPs) with and without an inert (undoped NaYF₄) shell have been successfully synthesized and the effects of shell thickness on the upconversion luminescence (UCL) and temperature sensing properties were systematically investigated. It was found that the NaYF₄ shell and its thickness do not affect the R_HS values and thermal sensitivity, but can obviously improve the UCL intensity of NaYF₄:Yb³⁺, Er³⁺ UCNPs. It implies that the core-shell structured NaYF₄:Yb³⁺, Er³⁺@NaYF₄ UCNPs with excellent UCL properties have great potential to be used as temperature sensing probes in biomedical fields, without considering the influences of the shell thickness on their temperature sensing properties.

Abstract: Composite nanostructures of NaYF₄:Yb³⁺, Er³⁺@Au have been successfully prepared by attaching gold nanoparticles onto the surface of NaYF₄: Yb³⁺, Er³⁺ upconversion nanoparticles (UCNPs). NaYF₄ inert shell was used to adjust the separation distance between gold nanoparticles and UCNPs. Effects of the gold nanoparticles on their upconversion luminescent (UCL), temperature sensing and photothermal therapy properties were systematically investigated. For all samples, a slight decrease of the UCL intensity was observed after gold nanoparticles attachment, suggesting that the nonradiative quenching effect is the dominant interaction between UCNPs and gold nanoparticles. However, the reduction of the UCL intensity is negligible due to the significant improvement of UCL properties by NaYF₄ shell. In addition, the gold attachment can obviously improve the photothermal conversion effect, but do not affect the temperature sensing properties of NaYF₄:Yb³⁺, Er³⁺ UCNPs, indicating their high capability for multifunctional applications in biomedical fields.

Abstract: Long afterglow phosphor is a special energy-saving material, which can store the energy of light irradiation and release light slowly. Ultrafine aluminate long afterglow phosphor is commonly prepared by the jet milling method. This method results in weak brightness, which restricts its application in delicate printing or textiles. In this study, fine particle aluminate phosphor (5μm) was coated by alumina, and then re-reduced under a high temperature. The alumina film works as a barrier layer, which protects the particles from sintering. The re-reduced phosphor had double afterglow brightness, and the size of the particle retained original level. The influences of pH value and KOH adding speed were investigated, the optimized parameters are: pH = 5, KOH adding speed = 2 ml/min.

Abstract: Mg doped BaAl₁₂O₁₉:Mn²⁺ phosphor is one of the most efficient green phosphors for PDP. It is difficult to prepare the phosphor both have small particle size (< 3μm) and high luminescence. In the present work, a BaAl₁₂O₁₉:Mn²⁺ phosphor with small particle size was synthesized by the chemical co-precipitation method. Phase transformation and particle growth process during calcining process were investigated. The nucleation process was also discussed. The results show that, the phase transformation is complicated, the transition phases include BaCO₃, γ-Al₂O₃, BaF₂, BaAl₂O₄ and two phases contain Mn; The BaAl₁₂O₁₉ phase is formed from the reaction between BaAl₂O₄ phase and γ-Al₂O₃ phase, no a-Al₂O₃ phase appears during the entire process; The formation temperature of pure BaAl₁₂O₁₉ phase is 1200°C, which is lower than that in the high-temperature solid state reaction method. High efficiency BaAl₁₂O₁₉:Mn²⁺ phosphor with small particle size (< 2μm) and hexagonal flaky shape can be prepared by this method.