A Facile Method Using a Flux to Improve Quantum Efficiency of Submicron Particle Sized Phosphors for Solid-State Lighting Applications

Abstract

This work successfully verified that the addition of a flux (NH 4 F, NH 4 Cl, and H 3 BO 3 ) during synthesis has an impact on the crystallite size and quantum efficiency of submicron-sized particles of CaMgSi 2 O 6 :Eu 2+ phosphors. The addition of NH 4 F or NH 4 Cl increased the crystallite size in the submicron-sized particles, yielding an increase in emission intensity and quantum efficiency. On the other hand, the use of the H 3 BO 3 flux crystallized a secondary phase, SiO 2 , and changed the lattice parameters, which degraded the luminescent properties. In addition, an excessive amount of NH 4 Cl was examined, resulting in nucleation of a secondary phase, CaSiO 3 , which changed the lattice parameters with no improvement in luminescent properties. These results demonstrate that the addition of a flux could be a method to improve the quantum efficiency of submicron-sized particles composed of nanocrystallites; however, a judicious choice of the flux composition and amount has to be carefully considered.

Controlling the europium oxidation state in diopside through flux concentration

“…In the Al-modified samples, the 4-fold coordinated Si 4+ sites (0.26 Å) are partially substituted by Al 3+ ions (0.39 Å in 4-fold coordination). 7,23,25,[31][32][33][34][35] The X-ray diffraction patterns of the investigated materials series show that regardless of the flux concentration, the obtained products are characterised by the pure phase of CaMgSi 2 O 6 (PDF 04-011-6810). The diffraction patterns do not possess signals from additional impurity phases.…”

“…The point group symmetry of the Ca sites is C 2 . 23,25 The ionic radii of the 8-fold coordinated Ca 2+ and Eu 3+ are equal to 1.12 and 1.07 Å, respectively, while the ionic radius of 6-fold coordinated Mg 2+ is equal to 0.72 Å. Due to the similarity of the radius, the Eu ions are expected to occupy Ca sites rather than Mg sites.…”

“…22,23 The solid-state synthesis of CaMgSi 2 O 6 is usually performed using a flux to obtain a single-phased, well-crystallized product. 18,19,[23][24][25][26][27][28][29] In this work, we describe the research conducted on the CaMgSi 2 O 6 matrix doped with europium and co-doped with aluminium ions to tune the oxidation states of europium in the material. The solid-state synthesis allowed us to obtain different series of CaMgSi 2 O 6 -based luminescent materials.…”

“…There is only one crystallographic site of Ca 2+ , 8-fold coordinated; Mg 2+ sites are 6-fold coordinated, while Si 4+ sites are 4-fold coordinated. The point group symmetry of the Ca sites is C 2 23,25. The ionic radii of the 8-fold coordinated Ca 2+ and Eu 3+ are equal to 1.12 and 1.07 Å, respectively, while the ionic radius of 6-fold coordinated Mg 2+ is equal to 0.72 Å.…”

Recent progress on lanthanide-based long persistent phosphors: an overview

“…12(c) depicts the crystal structure of CaMgSi 2 O 6 and coordination of Ca and Mg in the formed crystal structure. 117 The phosphor had characteristic red emission due to Mn 2+ ( 4 T 1 -6 A 1 ). Co-doping with lanthanides led to major intense emissions in the near-infrared region (generally utilised region for biological studies).…”