Role of Oxygen Vacancy on the Photoluminescence of BaMgSiO₄:Eu Phosphors: Experimental and Theoretical Analysis

Abstract

Pure BaMgSiO4:Eu(2+) phosphor, prepared by a solid state reaction method under N2 atmosphere, exhibited a strong green emission at 500 nm and a weak emission at 405 nm. Heat treatment under NH3 atmosphere causes changes in the PL intensity: the green emission at 500 nm gradually decreases and completely disappears after heat treatment for 3 h, whereas a new blue emission peak, centered at 445 nm, appears and becomes very strong. The results of the analyses with electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS) spectroscopy suggest that the heat treatment causes the generation of a large amount of oxygen vacancies. This resulted in the aforementioned color changes of the BaMgSiO4:Eu phosphor, which are confirmed by the results of DFT+U calculations. In particular, these calculations showed that Eu prefers to occupy Ba(3) sites, which are six coordinated to oxygen atoms. The emission at 500 nm was attributed to the 4f-5d transition energy of Eu in Ba(3) site, calculated as 2.54 eV. It was also shown that Eu 4f energy level decreases when oxygen is removed from the oxygen position adjacent to Eu, which results in a larger Eu 4f-5d transition energy and shorter wavelengths of emission peaks.

A simple way to synthesize anatase with high thermal stability

“…In order to confirm that the third octahedron prefers to join the existing dioctahedron by sharing an edge in the high OH -concentration, we performed first-principles calculations to compare the theoretical energy of different connections [34,35]. Based on the Ti OH ð Þ 2À 6 octahedron, we constructed two Ti 3 (OH) 14 2-clusters, one is the linear chain of octahedron corresponding to rutile (Fig.…”

Reversible Upconversion Luminescence Modification Based on Photochromism in BaMgSiO4:Yb3+,Tb3+ Ceramics for Anti‐Counterfeiting Applications

“…The Ba 2+ in the BaMgSiO 4 host has three different sites with coordination numbers (CN) of 9, 9, and 6. The radius of Ba 2+ is ≈1.47 and 1.35 Å in the 9 and 6 coordinate polyhedrons, respectively, which is larger than those of Yb 3+ (0.868 Å for CN = 6 and 1.042 Å for CN = 9) and Tb 3+ (0.923 Å for CN = 6 and 1. 095 Å for CN = 9).…”

“…The BMS ceramic exhibited an obvious absorption band centered at ≈254 nm and ranging from 200 to 400 nm, which was attributed to the absorption of the BaMgSiO 4 host. After doping with Yb 3+ and Tb 3+ , the absorption band at 254 nm exhibited a redshift due to a reduction of the band gap . Another absorption band located at 220 nm was observed in the BMS:Yb,Tb ceramic, which was attributed to Tb 3+ /Yb 3+ –O 2− charge transfer .…”

Preparation of Sr1−xCaxLiAl3N4:Eu2+ Solid Solutions and Their Photoluminescence Properties

“…It is clearly seen that the relative total energy decreases with the increase in Ca in Sr(I) sites. Accordingly, Ca is strongly prone to being accommodated in Sr(I) sites …”