The development of a sensitive α-NaYF4:Yb3+,Er3+ solid-phase upconverting platform (UCP) was realized using Moringa oleifera leaf extract for selective detection of the trivalent arsenic ion [As(iii)] contamination in drinking water. The presence of polyphenols in the leaf extract were shown to induce luminescence resonance transfer (LRET), thereby diminishing the Er3+ emission (red and green band) when activated by 980 nm excitation. However, the addition of As(iii) species interrupted the LRET process and restored the emissions proportionately. This feature allowed the platform to selectively detect arsenic pollution in water below the safe limit of 10 ppt. The uniqueness of UCP lies in monitoring the As(iii) contamination in samples containing heavy ions (Cd2+ and Hg2+) also, without an apparent effect on the signal reproducibility. The UCP was also found to be insensitive to other interfering ions including Pb2+, H2PO4-, F-, Cl-, Ca2+, Mg2+, Sn2+, Cr6+, Fe2+ and Co2+, if present.