Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016)
    Energy Harvesting & Storage Wednesday Sessions
       Session EH-WeP

Paper EH-WeP9
Improved Thermo-stability of (NH4)2SiF6 Fluorescent Microparticles with the Phosphoric Acids

Wednesday, December 14, 2016, 4:00 pm, Room Mauka

Session: Energy Harvesting & Storage Poster Session
Presenter: Aoi Tokiwa, Tokyo Denki University, Japan
Correspondent: Click to Email
Ammonium hexafluorosilicate ((NH4)2SiF6) microparticles, are one of novel phosphor, possess excellent features such as a high-efficient fluorescence and robust photo-stability, compared to other silicon (Si)-based ones. Because of these advantages, they are a promising candidate for the applications to light emitting diodes (LEDs), opto-electronic integrated circuits (OEICs) and solar cells. However, the microparticles may be restricted the adaptable environment so as to cause the rapid degradation of fluorescence intensity under temperature above 200℃. Therefore, the improvement of heatproof temperature is of crucial importance. As a one of the heat-resistance materials, the phosphoric acids are known to have effective features for the products such as flame-retardant plastics and rubber. In this presentation, we will discuss the thermo-stable effect of the (NH4)2SiF6 fluorescent microparticles with the phosphoric acids. The fluorescent microparticles were synthesized by the chemical reaction of vaporized hydrofluoric nitric acid with Si powders and P powders in closed container. The obtained microparticles had a mean diameter of approximately 10 - 30 μm, and were composed of (NH4)2SiF6/phosphorus oxide composites as major ingredients. To investigate the thermo-stability of the fluorescent microparticles, they were annealed from room temperature to 300 oC for 30 min in the atmosphere. The microparticles could be dramatically enhanced the heatproof temperature by adding the phosphoric acids, showing the stable fluorescence even after 300 oC annealing. It is clarified from Fourier transforms infrared (FT-IR) analysis that the improved thermos-stability is mainly due to the formation of Si-O bond with the stronger binding energy at the interface region between the (NH4)2SiF6 and the phosphorus oxide. It should be noted that the annealed microparticles at 300 oC could be visible to the naked eye. Therefore, the introduction of the phosphoric acids into the (NH4)2SiF6 fluorescent microparticles would become a dominant tool for the development of the thermally stable phosphor.