Balancing intermediate state decay rates for efficient Pr3+ visible-to-UVC upconversion: the case of β-Y2Si2O7:Pr3+

Materials that convert visible light into ultraviolet radiation have recently been studied for potential application to new catalytic and antimicrobial technologies. Conversion efficiencies of reported phosphors, however, have remained much lower than the more well-known IR-to-visible upconversion systems, due to a lack of lanthanide activator ions well suited for the required energy transfer mechanisms. Herein, the ceramic pyrosilicate beta-Y2Si2O7:Pr3+ was prepared for the first time and its visible-to-UVC upconversion efficiency was optimized. The resulting material showed the most efficient upconversion of this type to date, with a 3.9-fold improvement over the compositionally similar X2-Y2SiO5:Pr3+ benchmark material. Analysis of both the steady-state and time-dependent luminescence behavior revealed that a relatively short-lived P-3(J) intermediate state - normally considered detrimental to Pr3+ upconversion - in fact contributed to its efficacy. The pyrosilicate host also resulted in a much longer D-1(2) luminescence lifetime, the origins of which are speculated to relate to the precise spacing of the 4f states. Based on the results, we discuss revised criteria for the ideal Pr3+ photophysical behavior and host requirements for maximizing UVC conversion efficiency.