145. A METHOD TO IMPROVE QUANTUM EFFICIENCY OF NANOSIZED PHOSPHORS FOR NEAR UV-LEDS

Department: Mechanical & Aerospace Engineering
Faculty Advisor(s): Joanna M. McKittrick | Olivia A. Graeve | Gustavo Hirata

Primary Student
Name: Jungmin Ha
Email: juh061@ucsd.edu
Phone: 858-284-9016
Grad Year: 2018

Student Collaborators
Ekaterina Novitskaya, eevdokim@ucsd.edu

Abstract
Bulk phosphors have widely researched by the convenient solid-state method for a nUV-LED. This method synthesized high crystallite size phosphors having high quantum efficiency, but decreases packing density on the device and generates light-scattering effect. In order to overcome this issue, phosphors have particles size requirements: small size, narrow size distribution (non-agglomerated) and chemical and thermal stability. If the phosphor particles radii are significantly less than ~400 nm of the exciting radiation, these particles will negligibly scatter visible and UV radiation. However, phosphors in the nano-size regime have poor quantum efficiency compared to phosphors in the micron-sized range. This work studies the flux effect on the quantum efficiency of nano-sized phosphors without particles size change. We prepared nano-sized CaMgSi2O6:Eu2+ by co-precipitation reaction using a flux, NH4F, NH4Cl, or H3BO3 for blue-emitting phosphors, and then confirmed the flux effect on the phosphors properties. Typically, flux is used in the bulk phosphors, not nano-sized phosphors, and helps diffusion of atoms in the materials, influencing on properties of phosphors. When adding the flux in this material, the crystallite size of the phosphors increase from ~20 nm to ~40 nm but the particles size is unchanged, which is confirmed by X-ray Diffraction and Scanning Electron Microscopy. The emission wavelength of CaMgSi2O6:Eu2+ is 450 nm under near UV range in the Photoluminesce Spectroscopy. The intensity of emission wavelength is about twice increased comparing to the phosphors without a flux when 5wt% of NH4F is used as a flux, indicating the quantum efficiency is improved. This work showed that flux could be a great factor to improve quantum efficiency in the phosphors with nano-sized particles.

Industry Application Area(s)
Energy/Clean technology | Materials

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