Design,Fabrication And Excitation Quenching Mechanism Of Luminescent Materials For Laser Lighting

High-brightness white light sources are greatly demanded in projection,vehicle lighting,stage lighting,medical lighting,defense and other application areas.The"efficiency droop" of light-emitting diodes(LEDs)seriously limits the maximum luminance of the current LED lighting devices.Compared with blue LEDs,blue laser diodes(LDs)are perfect excitation sources for high-brightness lighting applications owning to the advantages of high luminance,small emitting area and small beam divergence.However,the high-power-desnity excitation brings great challenges to the luminescent materials and the shortcomings of the traditional luminescent materials,such as low thermal conductivity,low luminance,poor light uniformity,low color rendering index,optical saturation and etc.must be overcomed.In this dissertation,we explore the fabrication methods and design criteria of luminescent materials for the laser lighting applications and the optical excitation quenching mechanism of the luminescent materials under laser excitation was systematically investigated.The main contents and results are listed as below:1)A novel architecture based on the phosphor-in-glass(PiG)film and sapphire substrate is proposed and the luminous efficiency of the lighting device is greatly improved by introducing the one-dimensional photonic crystal to the architecture.The PiG films possess the advantages of high luminous efficiency,ultra-high brightness and versatile structure.The white light can be easily obtained by controlling the thickness of the PiG film and the mass ratio of the phosphor to glass.By introducing scattering factors to the PiG film,an ideal balance between excellent packaging efficiency(90%)and high white light uniformity can be achieved.The PiG film can survive under the high power density excitatio1 of 11.2 Wmm-2 and the maxium luminance is high to 845 Mcdm-2.A high color rendering index of 74 was obtained by adding orange or red phosphor layer onto the YAG PiG film.This work maily focuses on some urgent problems,such as the scarcity of color converters,low thermal conductivity,low luminance and low color rendering index in laser lighting.By applying the PiG into the high-brightness lighting,the luminescent materials suitable for laser lighting are greatly expanded.2)Compared with the small laser spot size,the emitting area of traditional transparent phosphor ceramics is significantly expanded,which reduces the maxium luminance of the phosphor ceramics.By introducing spherical pores into the the YAG:Ce transparent ceramics,a series of high scattering cermaics with controllable porosities were prepared.The high scattering ceramic could effectively limit the light propagation of the conversion light,leading to the point light emission characteristic of the phosphor ceramic.In addition,the beam divergence of the emission light is greatly reduced.The white light color coordinates can be obtatined by phosphor ceramic with porosity of 15%and the luminous flux is 855 lm under the power density of 7.92 wmm2.The maximum lumen density of the white light is～1710 lmmm-2,which is nearly five times higher than that of the state-of-the-art white LEDs.In rotary mode,the luminous efficiency and the luminous flux of the high scattering phosphor ceramic wheel are higher than those of low scattering ceramic and an ultra-high luminous flux white light of 7199 lm was achieved under 28.6 W blue laser excitation.This work mainly focuses on the current problems of low luminance,low thermal conductivity and poor light uniformity of color converter for laser lighting,which provides a new design strategy for the high-brightenss white lighting technology.3)The non-thermal quenching effect of Ce3+and Eu2+doped phosphors under high-power-density excitation was systematically reported for the first time.Through experimental results and theoretical analysis,it is confirmed that the main mechanism of the optical excitation quenching is energy-transfer upconversion rather than groundstate depletion or excited-state absorption.The internal quantum efficiency of luminescent materials under the assumption of energy-transfer upconversion is established,and the physical factors affecting the quenching rate are reavealed,which is the fluorescence lifetime,activiator,matrix and absorption coefficient.This work lays a theoretical foundation for the design and optimization of luminescent materials for laser lighting and display.In the end of the dissertation,summary and prospect of research on laser lighting are outlined.