Abstract
Nitridosilicates are structurally built up on three-dimensional SiN4 tetrahedral networks, forming a very interesting class of materials with high thermomechanical properties, hardness, and wide band gap. Traditionally, nitridosilicates are often used as structural materials such as abrasive particles, cutting tools, turbine blade, etc. Recently, the luminescence of rare earth doped nitridosilicates has been extensively studied, and a novel family of luminescent materials has been developed. This paper reviews the synthesis, luminescence and applications of nitridosilicate phosphors, with emphasis on rare earth nitrides in the system of M-Si-Al-O-N (M = Li, Ca, Sr, Ba, La) and their applications in white LEDs. These phosphors exhibit interesting luminescent properties, such as red-shifted excitation and emission, small Stokes shift, small thermal quenching, and high conversion efficiency, enabling them to use as down-conversion luminescent materials in white LEDs with tunable color temperature and high color rendering index.
Highlights
Covalent nitridosilicate materials, such as Si3N4 and its solid solutions, have been long known as structural ceramics due to their excellent thermo-mechanical properties, high strength, high hardness, high chemical stability, etc
There were no suitable applications except pigment for nitride phosphors until the solid state lighting, i.e., white light-emitting diodes (LEDs), came on stage and subsequently developed very fast in recent years
Rare earth doped nitride phosphors have been emerged as a new class of luminescent materials, showing promising photoluminescent properties such as significantly red-shifted excitation and emission spectra, abundant emission colors, small thermal quenching, and high quantum efficiency
Summary
Covalent nitridosilicate materials, such as Si3N4 and its solid solutions, have been long known as structural ceramics due to their excellent thermo-mechanical properties, high strength, high hardness, high chemical stability, etc. Very interesting luminescence has been observed in rare-earth-doped nitridosilicate materials, which opens up totally new application fields for traditional nitridosilicate materials as phosphors in lamps, display, etc. The large crystal field splitting is due to the large formal charge of N3- compared to O2-; and the nephelauxetic effect is attributed to the strong covalent chemical bonding between rare earth ions and ligand. There were no suitable applications except pigment for nitride phosphors until the solid state lighting, i.e., white LEDs, came on stage and subsequently developed very fast in recent years. As current ultraviolet (UV) LEDs have relatively low quantum efficiency and brightness, and the degradation or damage of packaging materials and illuminated bodies occurs by UV light irradiation, using blue LEDs as the primary lighting source is the mainstream of pc-LEDs. Anyhow, no matter what kind of LED chips are used, phosphors for white LEDs should have high conversion efficiency of UV or blue light, and emit suitable colors with high brightness. This article reviews the synthesis, photoluminescence, and applications of nitride-based phosphors that have been reported recently
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