Synthesis, Structure, and Photoluminescence of a Novel Oxynitride BaYSi₂O₅N Activated by Eu²⁺ and Ce³⁺

Abstract

A novel oxynitride, BaYSi 2 O 5 N, has been synthesized by a solid-state reaction method. Its crystal structure was determined by single-crystal X-ray analysis. Eu 2+ -and Ce 3+-doped BaYSi 2 O 5 N exhibit broad blue emission with peaks around 459 and 412 nm under excitation at 250450 and 250370 nm, respectively. This is the first report on the synthesis of oxynitrides in the BaO-Y 2 O 3 -SiO 2 -Si 3 N 4 system. Keywords: Oxynitride | Phosphor | Novel compoundSolid-state lighting devices based on white light-emitting diodes (w-LEDs) rapidly became popular due to their advantages such as low energy consumption, long lifetime, less mercury usage, and compactness compared with those composed of conventional incandescent lamps and fluorescents.1,2 Brightness, whiteness, and other functional abilities of the most prevalent w-LEDs, that is, phosphor-converted w-LEDs, are strongly dependent on phosphors.2,3 Therefore, exploration of new phosphors is one of the important subjects in the fabrication of high-performance w-LEDs.There are mainly two approaches to find new phosphors; utilization of known compounds and their derivatives as hosts, 4 or exploration of new compounds. To discover new compounds, some research groups use their own methods. 511 Our group succeeded in the development of new compounds capable of hosts for Eu 2+ -activated phosphors with giving a contrast in the ionic radii of constituent ions by substitution of Sr 2+ or Ca 2+ for Ba 2+ in Ba 4 Al 2 S 7 or NaBaPO 4 , respectively. 9,10 On the other hand, oxynitrides are one of the promising host groups for phosphors because some oxynitrides such as SiAlON, Ba 3 Si 6 O 12 N 2 , and their related materials exhibit excellent luminescent properties, especially low thermal quencing.12 Based on the background described above, we searched for new oxynitride compounds with the concept of contrasts in constituent elements with respects to not only the ionic radii but also oxidation numbers ( Figure S1) N) was mixed. The pellets were put in a carbon crucible and calcined at 1573 K for 4 h under 100 mL min ¹1 of N 2 flow. After cooling to room temperature, they were ground into powders. To grow single crystals without any activator, after calcination at 1573 K for 4 h, it was slowly cooled to 1373 K at a rate of 25 K h ¹1 and to 1173 K at a rate of 50 K h ¹1. Colorless plate-like crystals were obtained and cut into pieces. One crystal with dimensions of 0.040 mm © 0.037 mm © 0.030 mm was used for single-crystal X-ray diffraction (XRD) analysis (Rigaku; R-AXIS RAPID II) using Mo Kα radiation at 296 K. The obtained powders were characterized by powder XRD analysis (Bruker AXS; D2 Phaser) and PL spectroscopy at room temperature (Hitachi; F-7100). Rietveld refinement was performed using the TOPAS 4.2 program (Bruker). The nitrogen contents in the samples were analyzed with an oxygen/ nitrogen analyzer (Horiba; EMGA-620W). Thermogravimetricdifferential thermal analysis (TG-DTA) was also conducted in air (Shimadzu; DTG-60H).The single-crystal XRD and nitrogen content ...