(Alumino)Silicate-based Oxide/oxynitride Phosphors For White LED Lighting

Lighting plays a very important role in the history of human development. Compared to the traditional incandescence lamp and fluorescence lamp, white LED (WLED) lighting has many advantages, such as energy saving, long lifetime, environmental friendship, extensive applications, fast response, and so on. In the phosphor conversion-based white LED, phosphor is the key factors which determine the quality of LED light source, for example, the correlated color temperature (CCT), color rendering index (CRI), luminous efficacy, et al. At present, commercial WLEDs are fabricated by combining a blue chip and YAG:Ce yellow phosphor. In this device, due to color deficiency in the red spectral region, the generated white light usually exhibits a low CRI and a high CCT. Recently, the (oxy)nitride phosphors have been widely researched and have promising applications in the field of white LED due to their high quantum efficiency (QE), long-wavelength emission, and excellent thermal and chemical stability. However, the difficulties in preparation and high raw materials cost limit their applications in WLED. Thus, focusing on the above problems, this thesis is committed to find and synthesize new (oxy)nitride phosphors which can be efficiently excited by blue light by a low-cost process. Their optical properties will be improved by optimizing the synthesis process and codoping sensitizer. Finally, the synthesized phosphors were successfully applied to white LED devices by combining with blue LED chip to improve CRI and lifetime.The main research contents of this thesis are summarized as follows:(1) Lu3(Al,M)5(O,N)12:Ce3+(M=Si,B) phosphors were successfully synthesized by a conventional solid-state reaction method. The effect of Si4+-N3-、B3+-N3-、Al3+-N3- bonds incorporation on the optical properties of LuAG:Ce3+ phosphor was investigated. The incorporation of Si4+-N3- leads to a distinct red shift and broadening of photoluminescent spectrum. Adding NaF as a flux can greatly improve the emission intensity of the Lu3Al4.79Si0.2iO11.79N0.21:Ce3+ phosphor. The incorporation of B3+-N3-, Al3+-N3- leads a marked increment in the photoluminescent intensity rather than changing the shape and position of photoluminescent spectrum. Also, the addition of charge compensating agent can further improve the emission intensity.(2) SrSi2O2N2:Eu2+, Mn2+/Ce3+ and Sr2Si5N8:Eu2+phosphors were successfully synthesized by a simple sol-gel method. Their luminescence properties, quantum yield, and thermal stability were investigated systematically. The emission intensity of Eu2+ ions in green light is greatly both enhanced by introducing Mn2+ or Ce3+ ions into SrSi2O2N2:Eu2+ due to the coexcitation and energy transfer between Mn2+ and Eu2+. However, Mn2+ is better than Ce3+. The energy transfer probability from Mn2+ to Eu2+ depends strongly on the Mn2+ concentrations, which is maximized at 2.0 at%. Simultaneously, quantum efficiency and thermal stability in SrSi2O2N2:0.03Eu2+,0.02Mn2+ is dramatically improved. A pure phase Sr2Si5N8:Eu2+ phosphor was successfully synthesized by a simple sol-gel method. Its excitation spectrum cover from near UV to bule light region and emission spectrum locate at 615nm. When it is applied to WLEDs by combining a blue chip and YAG:Ce yellow phosphor, the emission in red light of Sr2Si5N8:Eu2+ just makes up for the color deficiency of YAG:Ce in the red spectral region. As a result, the CRI of WLED can be improved.(3) γ-Ca2SiO4:Ce3+/Eu2+ and α’L-Ca2SiO4:Ce3+/Eu2+ phosphors were successfully synthesized by a simple sol-gel method. Their structure and luminescence properties were investigated in detail. γ-Ca2Si04:Ce3+/Eu2+ can be synthesized by introducing Al3+ ions into Ca2SiO4 as a crystal stabilizer with 6 at% concentration. The excitation spectrum of γ-Ca2SiO4:Ce3+ covers the whole region from UV to blue light, and the emission band peaks at 565 nm with a full width at half-maximum (FWHM) of 105 nm. γ-Ca2SiO4:Ce3+ phosphor also shows an excellent thermal stability, which enhances its potential for white LED lighting applications. γ-Ca2SiO4:Eu2+ phosphor gives a yellow emission peaked at 540 nm excited by 365 nm. α’L-Ca2SiO4:Ce3+/Eu2+ can be synthesized by introducing P5+ ions as a crystal stabilizer and the optical properties reaches the optimization at 0.2 P5+ concentration. α’L-Ca2SiO4:0.02Eu2+ exhibits an excitation spectrum covering from UV to blue region and emits the green-blue light peaked at 498 nm. And also, α’L-Ca2SiO4:Ce3+ phosphor gives a blue emission peaked at 430 nm excited by 365 nm.(4) White LED flat lamps were fabricated by using phosphors synthesized in the present work combining with a blue LED chip, and their optical properties were investigated. The warm white LED flat lamps with CRI as high as 71～88, CCT of 3990～8700 K and luminous efficiency of 50～81 lm/W are successfully realized by using a single host phosphor combined with a blue LED chip. The warm white LED flat lamps with CRI around 90 (maximized to 94), CCT ranging from 3500 to 8000 K and luminous efficiency of 66～79 lm/W are successfully realized by using the synthesized red and green phosphors combining with a blue LED chip. The warm white LED sources can satisfy with different application requirements under various environments by tuning the ratio of red to green phosphors.