Uranium-Sensitized Luminescence Enhancement in Li2B4O7:U6+,Eu3+ and Potential Application towards Color-Tunable Phosphors and Actinide Sensor

Actinide–lanthanide interaction has led to many fascinating results in the past pertaining to applications in the area of energy, health, and the environment. In this work, we utilized UO22+ ion codoping to enhance the luminescent properties of the europium ion in a Li2B4O7 (LTB) host. We could achieve 75% energy transfer efficiency, leading to almost doubling of internal quantum yield (IQY) from ∼34 to 64%. The efficacy of energy transfer from a uranyl to a europium ion and enhancement in europium emission was clearly demonstrated using density functional theory calculations, and it proceeds via formation of a UO2–Eu coordination complex. Because of the different extent of UO22+ → Eu3+ energy transfer at different europium ion concentrations, color-tunable emission from green–yellow–near-white could be achieved. The optical enhancement has also been explained by detailed electronic structure analysis of LTB in the presence of Eu and U. Here, we also present the feasibility for sensing uranyl (VI) ions through the exploration of a unique Förster resonance energy transfer process to europium(III) using selective excitation of a near-UV 320 nm photon. This work on the LTB:U6+,Eu3+ luminescent phosphor displays the first example demonstrating UO22+ → Eu3+ energy-transfer-induced enhancement in IQY and applying the same for designing color-tunable phosphor and an on–off fluorescent sensor for uranyl (VI) ions.