Air and Thermally Stable Fluoride Bridged Rare-Earth Clusters Showing Intense Photoluminescence and Potential LED Application

Fluoride based lattice is attractive for reducing phonon-induced quenching in rare-earth (RE) based luminescent materials. However, due to the strong affinity between RE and oxygen, the synthesis of fluoride-based complexes has to be protected under anhydrous conditions, and many known fluoride bridged RE clusters are unstable in air. Here, by using the "mixed-ligand" strategy a family of fluoride bridged RE clusters is synthesized, namely RE₁₆(μ₄-F)₆(μ₃-F)₁₂(^tBuCOO)₁₈[N(CH₂CH₂O)₃]₄ (RE = Eu, EuFC-16; RE = Tb, TbFC-16), which are highly stable in air and decomposed thermally only when heating above 435 °C. Moreover, both clusters exhibit high photoluminescence quantum yields (PLQY_EuFC-16 = 87.7%, PLQY_TbFC-16 = 99.0%). Upon warming, EuFC-16 and TbFC-16 display excellent structural, thermal, and chroma stability. Thus, EuFC-16 and TbFC-16 have the potential to be used in light-emitting diode (LED) devices, offering many advantages over commercial phosphors. First, both clusters are soluble in UV-curable resin at any mixing rate, and the emission colors can be tuned from magenta, turquoise, willow green, and ivory to pure white if mixing blue phosphor BAM:Eu²⁺. Second, the clusters are hydrophobic, and the LEDs work well after soaking in water, indicating a good quality for outdoor lighting.