With increasing concerns about energy savings, environmental protection, and life quality, novel lighting sources that exhibit higher luminous efficacy, energy efficiency, and longevity are continuously pursued. White light-emitting-diodes (WLED) is considered the third revolution of the lighting industry, following the introduction of incandescent bulbs and fluorescent lamps. White light-emitting-diodes is a new lighting source that is based on semiconductor devices, with the light emitted by solid-state electroluminescence, which has great potential to significantly surpass the energy efficiencies of incandescent and fluorescent lamps, and thus promises huge energy savings and reduction of greenhouse gas emissions. As a novel light source, WLED offers the following advantages over traditional lighting sources, such as high luminous efficiency, tunable color temperatures, high color rendering properties, and long lifetime.
For phosphor-converted white LEDs, phosphors play a key role in downconverting the wavelength of the LED chip into suitable visible light, and finally in controlling the light quality of white LEDs. Consequently, downconversion phosphors are one of the key materials in white LED technologies.
Nitride phosphors have been proven to be the most encouraging luminescent materials in WLED. They have better chemical stability than previously used alkaline earth sulfide (e.g., SrS:Eu) and thiogallate (e.g., SrGa2S4:Eu) phosphors that are more sensitive to moisture. In addition, in comparison with garnet (i.e., YAG:Ce) and orthosilicate (i.e., Sr2SiO4:Eu) phosphors that are commonly applied in solid state lighting, nitride phosphors have more abundant emission colors and superior thermal stability due to the diversity of crystal structure. Thanks to their unique photoluminescence spectra, high quantum efficiency and high reliability, nitride phosphors are very capable of producing white LEDs with high color rendition (general illumination)49–52 or wide color gamut (backlighting).