Study of Gd-induced shift of luminescence spectra of YGAG:Ce micropowders as a function of grain size

Four YGAG:Ce phosphors in the form of micropowders synthesized by solid-state reaction and the small-size fractions isolated thereof were thoroughly studied in order to establish the relationship between luminescent characteristics, size and the composition of the phosphor grains. Both photoluminescence (PL) and cathodoluminescence (CL) spectra were measured and analyzed. The PL spectra excited by the blue LED were taken from the powder samples differing in the content of key dopants (Ce, Gd) as controlled by inductively coupled plasma mass spectrometry (ICP-MS). The CL spectra excited by the electron beam of a scanning electron microscope (SEM) were taken from individual grains of various sizes (1-40 µm). It was found that in most cases the smaller is the grain size, the lower is the intensity of PL and the greater is the blue shift of spectra. This effect is strongly correlated with a content of Ce and Gd in the grains. The mechanisms of Gd-induced red shift of luminescence were considered in terms of the fine structure of CL spectra.