Luminescent Eu3+/Gd3+ co-doped hydroxyapatite for selective sensing Cr3+ and Cu2+ ions

Abstract

Both excess and deficiency of Cr3+ and Cu2+ ions can bring about certain abnormalities in human health, but it is still challenging to achieve great sensitivity and selectivity for sensing trace amount of copper and chromium ions due to the strong interference of coexisting ions in ambient water. To take advantage of excellent luminescence of rare earth (RE) ions and biodegradability and environmental friendliness of hydroxyapatite (HAP), novel luminescent Eu3+/Gd3+ co-doped hydroxyapatite (HAP/Eu-Gd) has been synthesized as a sensing material for the detection of Cu2+ and Cr3+ ions. Based on the fluorescence “turn-off” effect, Cr3+ and Cu2+ ions can be selectively recognized by their quenching fluorescence of the HAP/Eu-Gd. The HAP/Eu-Gd displays great sensitivity. Its limit of detection for Cu2+ and Cr3+ ions are 0.566 μM (35.967 μg/L) and 0.165 μM (8.579 μg/L), respectively, which are below the Cu2+ (2 mg/L) and Cr3+ (100 μg/L) contamination limits of drinking water stated from the United States Environmental Protection Agency. Moreover, the luminescence quenching mechanisms of the HAP/Eu-Gd for Cu2+ and Cr3+ ions were elucidated by X-ray diffraction, Fourier transform infrared spectra, UV-Vis adsorption spectra, photoluminescence studies and luminescence lifetime measurements. Our study paves the way for RE-doped HAP luminescent sensors in potential applications for metal ion detection.