Introducing Uranium as the Activator toward Highly Stable Narrow-Band Green Emitters with Near-Unity Quantum Efficiency

Searching for new green phosphors featured with a narrow
band,
small Stokes-shift, high thermal stability, and decent chemical resistance
is critical for white light emitting diodes (LEDs) in liquid-crystal
displays (LCDs). For the first time, we introduce a uranyl (UO22+) compound with inherently bright green emission
as the activator for fabricating high-performance phosphor-converted
LEDs. UO22+ was successfully incorporated into
a dense, rigid, UV-transparent, and photoluminescent borate framework
(Na­[(UO2)­B6O10(OH)]·2H2O (NaUBO-4)) exhibiting surprisingly high internal and external quantum
efficiencies (close to 100% and 92% for excitation at 260 nm, respectively),
low thermal quenching (96% of the initial emission intensity can be
maintained at 120 °C), and high luminous stability after long-term
exposure to moisture and UV radiation. Furthermore, the vibronically
coupled emission from UO22+ with relatively
narrow emission bands leading to a wide color range of 95% of the
National Television System Committee (NTSC) standard for a white LED
device, fabricated by a InGaN blue chip, green-emitting NaUBO-4, and
a commercially available red-emitting phosphor KSM:Mn4+. These results make depleted uranium extremely attractive for potential
applications as backlight units in wide-color-gamut LCDs.