Understanding the Defect Chemistry of CaAlSiN₃ Inorganic Phosphor Host Material for Solid State Lighting Applications

Lightning is a major source of world energy consumption, and the development of more efficient lighting technologies is of high importance. Light emitting diodes (LEDs) have been shown to achieve high efficiency, durability, and stability compared to conventional lighting. One way to produce LEDs is to combine blue- or UV- LED chip with one or more inorganic phosphor(s) that absorbs high-energy light from chip and down-convert to longer-wavelength. Phosphor-converted light emitting diodes, pc-LEDs, have attracted significant attention since different combinations of phosphors allow to tune the overall quality of light. Therefore, the development of novel inorganic phosphors with the desired properties has become a necessity to improve the performance of pc-LED devices.<br/><br/>CaAlSiN₃ (CASN) is a member of nitride group (Ca₃N₂ – AlN – Si₃N₄) and when doped with Eu²⁺ ions, produces a red light under blue excitation and, thus, is used as an inorganic phosphor in highly-efficient warm-white pc-LEDs.Several studies have shown that doped-CASN serves as a promising inorganic red phosphor due to its high quantum output, good thermal and chemical stability, and low thermal quenching. One of the important structural features of CASN is that Al³⁺ and Si⁴⁺ ions are randomly distributed among identical tetrahedral sites. The Al/Si disorder can influence the electronic and optical propertiies of host material. However, the defect chemistry in this material is not well understood and requires further research.<br/><br/>The goal of this project is the investigation of cation disorder in CASN and the analysis of the defect chemistry in this material using a combination of computational methods (including Density Functional Theory, cluster expansion, Monte Carlo simulations, Madelung analysis). The results of our investigations of the intrinsic defects and their influence on electronic and optical properties of CASN crystal material will be presented.