Research On Rare Earth Ions Doped Silicate Phosphors For W-LED And NaGdTiO₄ Upconversion Phosphors

Rare earth elements have superior luminescence properties due to their unique transition between electronically configured energy levels,such as long life,high luminous efficiency,wide spectral coverage,etc.They show great application value in fields of fluorescence,anti-counterfeiting,cancer treatment,solid-state lasers,white LEDs and upconversion devices.White LEDs have been used in lighting,displays and backlights due to their small size,long life,energy saving,environmental protection and high stability.Presently,commercial W-LEDs are typically manufactured by combining a blue LED chip with a yellow phosphor YAG:Ce³⁺.YAG:Ce³⁺phosphor is thermally quenched by the high temperature of the device,resulting in a shift in color coordinates and a decrease in luminous efficiency,thereby degrading device performance,which will affect the LED at work.Meanwhile,since this way of realizing a W-LED is due to the lack of a red emission section,it has the disadvantages of low color rendering index and high color temperature.Therefore,the development of high thermal stability red luminescent materials is of great significance for improving the performance ofW-LED devices.Upconversion materials have attracted great attention due to their potential application in temperature sensing.NaGdTiO₄powder has high mechanical strength and physical and chemical stability,and has outstanding advantages such as simple preparation process,low environmental requirements and low preparation cost,and there has a little research on upconversion about this matrix.Therefore,it is worth further research on the upconversion characteristics of the matrix and application in temperature sensing.The main research contents are as follows:The first chapter mainly introduces the rare earth element and electronic configuration,the realization principle,composition and development of white LED,the history of upconversion luminescence,the luminescence mechanism,the type and application of materials,and the principle of fluorescence temperature detection.The second chapter mainly studies the fabrication,structure and fluorescence characteristics of Ca₂Y₈?SiO₄?₆O₂:Eu³⁺phosphor materials and their applications in white LEDs.A high thermal stability Ca₂Y₈?SiO₄?₆O₂:Eu³⁺phosphor with hexagonal phase was synthesized by using high temperature solid phase method.The structure and morphology of the samples were characterized by X-ray diffraction and scanning electron microscopy.Diffraction peak shift to a larger angle in the XRD pattern,the change in the lattice constant obtained from the XRD refinement map,and the Stark splitting phenomenon in the emission spectrum indicate that Eu³⁺has entered the matrix lattice.The obtained sample Ca₂Y₈?SiO₄?₆O₂:0.3Eu³⁺was packaged with blue phosphor BaMgAl₁₀O₁₇:Eu²⁺and green phosphor BaSiO₄:Eu²⁺and a near-ultraviolet LED chip?395 nm?.Under different current?20-140 mA?excitation,warm white light with a color rendering index higher than 92 and a color temperature lower than4000 K was obtained.It shows that Ca₂Y₈?SiO₄?₆O₂:Eu³⁺has very good potential applications in the field of white LED.The content of the third chapter is about the preparation,structure and temperature sensing characteristics of NaGdTiO₄:Yb³⁺/Tm³⁺phosphor.An orthohombic NaGdTiO₄:Yb³⁺/Tm³⁺upconversion material was synthesized by a high temperature solid state method.Meanwhile,the shift to smaller angle of the diffraction peaks in the XRD pattern and the Stark splitting phenomenon of the emission spectrum indicate that Yb³⁺/Tm³⁺ions have successfully entered into the matrix lattice.Based on the larger energy level gap between ³F_2,3,3 and ³H₄ energy states of Tm³⁺ions,The temperature sensing performance of NaGdTiO₄:Yb³⁺/Tm³⁺was studied.The maximum relative sensitivity at 433 K was 1.36%K^-1.The results show that NaGdTiO₄:Yb³⁺/Tm³⁺has a good application prospect in temperature detection.The structure and density of states of NaGdTiO₄ matrix were calculated by First-Principles.The fourth chapter summarizes and forecasts the main work of this thesis.