Luminescence Properties Of Er³⁺ Doped Upconversion Luminescence Materials Under 1550nm Excitation

Rare earth ions doped upconversion luminescent (UCL) materials have become a hot spot of current research. Due to the face that UCL materials have been widely used in display, security, biological fluorescent tags, etc. There are rare reports about the 1550nm laser used as excitation source in that most researchers used 980nm laser as excitation source when discussing the mechanism of upconversion. In view of this, we use the fluoride and sulphur oxide host material as research object, focusing on its UCL performance under 1550nm excitation. The major works are shown as follows:1. Synthesizing hexagonal phase NaYF^ Yb3+, Er3+ microcrystals through hydrothermal method and discussing the influence from different conditions on the morphology and UCL properties of samples. NaYF4:Yb, Er is an efficient green UCL material under 980nm excitation. Both red and green light emissions were two-photon process and the optimum concentration of Er3+ was 2%. But the red emitting light composition increase obviously under 1550nm excitation, and the red and green light emissions are nearly three-photon process. Near infrared emission was obviously observed at the same time. The optimum concentration of Er3+ reached 9%. In conclusion, the UCL color of the samples can be slightly tuned through changing the excitation wavelength and the concentration of Er3+.2. Gd2O2S:Yb, Er and La2O2S:Yb, Er nanoparticles were prepared by homogeneous precipitation method combined with solid-sulfide method. Both Gd2O2S: Yb, Er and La2O2S:Yb, Er presented green emission and red emission under 980nm excitation. The component of green emission increased with the increasing pumping excitation, which led to the color of samples moves to the green areas. The emission peaks of two samples were the same under 1550nm excitation. However, the relative intensity of emission was obviously different. From that of 980nm, the red and green emission integral strength ratio (IR/IG) increased significantly, which improved the red color purity. In addition, we can observe near infrared emission at 789-839nm. The IR/IG of Gd2O2S:Yb, Er slightly increased with the increasing pumping excitation while the IR/IG of La2O2S:Yb, Er sample sharply decreased and its luminous color changed from red to orange red. Therefore, the emission color can be successively modulated by way of changing excitation wavelength and power.3. With Li2CO3 as fluxing agent, synthesizing Gd2O2S:Yb, Er and La2O2S:Yb, Er samples with the sulfur melting method through directly vulcanizing oxide precursor. The green UCL intensity of Gd2O2S:Yb, Er and La2O2S:Yb, Er samples are stronger than that of the red under 980nm excitation. However, both of them present more pure red emission under 1550nm excitation. As the excitation power increases, red component increases in Gd2O2S:Yb, Er samples and decreases in La2O2S Yb, Er sample. Therefore, the prepared Gd2O2S:Yb, Er with sulfur melting method is a more ideal one among red UCL materials.