INVESTIGATION OF COLORIMETRIC TRENDS IN RARE-EARTH CO-DOPED YPO₄

From detectors in scientific instrumentation to medical imaging devices and nuclear monitoring systems to LEDs seen in consumer products, phosphors are utilized in a myriad of applications experienced by both the general public and scientific community alike. For many phosphor applications, emission color and intensity are notably important features to consider. When phosphors are co-doped with rare-earth activators, the ability to predict emission intensity and color output becomes challenging due to competition kinetics and energy transfer between the dopants. During this study, correlation between trends in co-doped phosphor excitation and color output were analyzed to interpret optical behaviors originating from interdopant energy transfer and spatial separation through intercalation of co-doped activators. Color coordinates, excitation intensity trends, and excitation intensity ratios were obtained for crystalline Y1-x-yPO4:Tbx,Smy, Y1-x-yPO4:Eux,Tby, and Y1-x-yPO4:Eux,Smy (0.005 ≤ x ≤ 0.08 and 0.005 ≤ y ≤ 0.08) by utilizing vacuum ultraviolet (VUV) excitation spectroscopy. Through implementing energy transfer models established from prior studies, the color coordinate, excitation, and interdopant energy transfer behaviors of these co-doped phosphor systems were examined. From the co-doping of Eu3+, Sm3+, and Tb3+ into YPO4, energy transfer from Tb3+ was observed to occur to Sm3+ and Eu3+, while no energy transfer was observed between Eu3+ and Sm3+. Additionally, it was determined that the color coordinates generated from the co-doping of activators will shift linearly between the “pure” color coordinates of the single doped color coordinates of each activator. Furthermore, the accessible color coordinates of the co-doped phosphors are heavily dependent on the excitation wavelength.