Understanding the links between composition, polyhedral distortion, and luminescence properties in green-emitting β-Si6−zAlzOzN8−z:Eu2+ phosphors

Abstract

Inorganic phosphor materials play a crucial role in the creation of white light from blue and near-UV solid-state light-emitting diodes. Understanding the intricacies of the phosphor structure is key for setting the stage for improved, more efficient functionality. Average structure and coordination environment analysis of the robust and efficient green-emitting phosphor, β-SiAlON:Eu²⁺ (β-Si_6−zAl_zO_zN_8−zEu_0.009), is combined here with a range of property measurements to elucidate the role of Al content (z) in luminescence properties, including the red shift of emission and the thermal quenching of luminescence as a function of increasing Al content z. Average structure techniques reveal changes in polyhedral distortion with increasing z for the 9-coordinate Eu site in β-SiAlON:Eu²⁺. X-ray absorption near edge structure (XANES) is used to confirm that the majority of the activator Eu is in the Eu²⁺ state, exhibiting the symmetry-allowed and efficient 4f⁷5d⁰ → 4f⁶5d¹ transitions. Room temperature and temperature-dependent luminescence indicate a curious increase in thermal stability with increasing z over a small range due to an increasing barrier for thermal ionization, which is correlated to an increase in the quantum yield of the phosphor.