Improvement of Luminescence Properties and Particle Growth of AlN Phosphors By Si-Doping

Aluminum Nitride (AlN) has been regarded as a promising material for ceramic phosphors. Recently, we have developed a high efficiency blue AlN phosphor by co-doping with Si and Eu [1-2]. It has been proven that particle have grown rapidly with the highest luminescent intensity on the proper Si doping. Now, it is important to understand the role of Si on AlN particle growth and luminescence enhancement.

For this purpose, AlN powders doped with Si from 0 to 4 at. % were prepared using gas-pressure sintering (GPS) furnace at 1950°C in N₂ atmosphere. Firstly, particle size, phases and luminescence spectra of Si-doped AlN powder were investigated using SEM, XRD and CL. Secondly, the defect were evaluated by EPR to identify the defects transitions. Finally, the particle growth mechanism was clarified by cross-sectional CL-EDS.

From 0.4 to 2.0 % Si, particle growth of AlN powders as well as ultraviolet emissions at 290 and 350 nm are enhanced. The 350 nm emission may be attributed to native AlN defects such as vacancy-oxygen complexes. The shoulder at 290 nm and 450 nm can be ascribed to the different states of Si related defects in AlN by EPR analysis. Cross sectional CL images show that the 1.6 % Si-doped AlN yields 280 nm emission at the surfaces of AlN particles (Fig. 1). Many particles are connected to each other with these bright surfaces. It suggests that the Si-rich surface may act as the binder of AlN particles and enhance the Ostwald growth.

References:

[1] T. Takeda et al., J. Mater. Chem., 20, 9948 (2010).

[2] B. Dierre et al., ECS J. Solid State Sci. Technol., 2, R126 (2013).

Figure:

Cross sectional SE (a), CL images taken at 280 nm (b), 350 nm (c) for 1.6% Si-doped AlN powders and schematics explanning the growth mechanism (d))