Extended Excitation Approach for Ultraviolet Phosphors via the White-to-Ultraviolet Upconversion

The development of ultraviolet light-emitting materials is attracting increased attention due to their important applications in many technological fields involving light mediated treatment and disinfection. Despite progress, further advancements in these materials have been hindered by the limited availability of excitation light sources. In this work, we utilize a convenient white flashlight as an excitation source to explore the upconverted emission performance of a series of ultraviolet phosphors, involving Tm3+, Er3+, Ho3+, Nd3+, or Pr3+ ion activated systems. As an illustration, we demonstrate that a Tm3+-doped yttrium phosphate (YPO4:Tm3+) exhibits ultraviolet emissions peaking at 289, 346, and 362 nm upon exposure to the flashlight. Spectroscopic investigations reveal that both energy-transfer upconversion and excited-state absorption schemes contribute to the excitation. Considering the widespread use of flashlights, white-light excitability presents a promising avenue for broadening the scope of functional ultraviolet phosphors.