The influence of Dy3+ ions concentration and annealing on the properties of LaGdSiO5:Dy3+ nanophosphors

Abstract

The influence of Dy3+ concentration and annealing on the structure and photoluminescence properties of lanthanum gadolinium oxyorthosilicate (LaGdSiO5) was studied in detail. The X-ray diffraction patterns of the samples annealed at 1000°C for 1h showed new peaks which were not observed in the as-prepared samples. Also some peaks which were in the as-prepared samples were not observed in the annealed samples. These observations suggest that there was phase transformation caused by annealing. The chemical composition and states of the as-prepared and annealed samples were analysed using time of flight secondary ion mass spectroscopy and X-ray photoelectron spectroscopy respectively. The excitation spectra of the as-prepared samples when monitoring the emission at 573nm using a monochromatic xenon lamp showed two peaks located at 227 and 241nm whose intensities varied with the Dy3+ concentration. However, after annealing, the intensity of the 241nm excitation peak decreased drastically. When the emission was monitored at 227 and 241nm, two prominent emission peaks located at 485 and 573nm which were ascribed respectively to the 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of Dy3+ were observed. When the samples were excited using a 325nm He–Cd laser, an additional broad emission peak was observed around 400 to 460nm which was ascribed to self-trapped excitons (STE) in SiO2. This broad peak decreased after annealing due to reduction in the defects concentration and the subsequent change in the CIE color coordinates. The mechanism of the STE emission is discussed.