White light emission from Sm-doped YAG ceramic controlled by the excitation wavelengths

Abstract

This work reports, for first time, on optically-driven white light emission from samarium-doped yttrium aluminum garnet ceramic, Sm-doped YAG. Nanocrystalline Sm-doped YAG sample has been prepared via co-precipitation method then transformed to bulk ceramic by sintering process using Spark Plasma Sintering (SPS) technique. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) are used to characterize the crystal structure of the nanocrystals. The micro-grains of the obtained ceramic have been demonstrated by scanning electron microscope (SEM). Photoluminescence (PL) and cathodoluminescence (CL) spectroscopies have been performed on the ceramic sample. It is found that the PL spectral features are strongly dependent on the excitation wavelength. Remarkable PL spectral overlapping between bluish-green band and reddish-orange lines related to host defects/impurities and Sm ions, respectively, has been obtained. In addition, controlling the relative PL spectral contributions from the host-related emission and Sm ions has been achieved by changing the excitation wavelengths. This led to manipulate the emission color coordinates as investigated by chromaticity diagram. Moreover, under certain excitation wavelengths, an intense white emission is observed with a naked eye. The origin of the white emission has been discussed in light of specific PL spectral overlapping from the host and Sm ion contributions. This work emphasizes on the role played by the host defects/impurities in the optical properties of ceramic materials that can be exploited in several lighting applications.