This article describes a green synthetic approach to prepare water dispersible perovskite-type Eu(3+) -doped KZnF3 nanoparticles, carried out using environmentally friendly microwave irradiation at low temperature (85 °C) with water as a solvent. Incorporation of Eu(3+) ions into the KZnF3 matrix is confirmed by strong red emission upon ultraviolet (UV) excitation of the nanoparticles. The nanoparticles are coated with poly(acrylic acid) (PAA), which enhances the dispersibility of the nanoparticles in hydrophilic solvents. The strong red emission from Eu(3+) ions is selectively quenched upon addition of Cu(II) ions, thus making the nanoparticles a potential Cu(II) sensing material. This sensing ability is highly reversible by the addition of ethylenediaminetetraacetic acid (EDTA), with recovery of almost 90 % of the luminescence. If the nanoparticles are strongly attached to a positively charged surface, dipping the surface in a Cu(II) solution leads to the quenching of Eu(3+) luminescence, which can be recovered after dipping in an EDTA solution. This process can be repeated for more than five cycles with only a slight decrease in the sensing ability. In addition to sensing, the strong luminescence from Eu(3+) -doped KZnF3 nanoparticles could be used as a tool for bioimaging.