Quenching of the Eu3+ Luminescence by Cu2+ Ions in the Nanosized Hydroxyapatite Designed for Future Bio-Detection

Abstract

The hydroxyapatite nanopowders of the Eu3+-doped, Cu2+-doped, and Eu3+/Cu2+-co-doped Ca10(PO4)6(OH)2 were prepared by a microwave-assisted hydrothermal method. The structural and morphological properties of the products were investigated by X-ray powder diffraction (XRD), transmission electron microscopy techniques (TEM), and infrared spectroscopy (FT-IR). The average crystal size and the unit cell parameters were calculated by a Rietveld refinement tool. The absorption, emission excitation, emission, and luminescence decay time were recorded and studied in detail. The 5D0 → 7F2 transition is the most intense transition. The Eu3+ ions occupied two independent crystallographic sites in these materials exhibited in emission spectra: one Ca(1) site with C3 symmetry and one Ca(2) sites with Cs symmetry. The Eu3+ emission is strongly quenched by Cu2+ ions, and the luminescence decay time is much shorter in the case of Eu3+/Cu2+ co-doped materials than in Eu3+-doped materials. The luminescence quenching mechanism as well as the schematic energy level diagram showing the Eu3+ emission quenching mechanism using Cu2+ ions are proposed. The electron paramagnetic resonance (EPR) technique revealed the existence of at least two different coordination environments for copper(II) ion.

Red-Emitting SrGa2O4:Cu2+ Phosphor with Super-Long Persistent Luminescence

“…The band around 340 nm might originate from the charge-transfer transition from O 2– to Cu 2+ , analogous to the charge-transfer absorption in the range of 300–400 nm for Na 2 ZnP 2 O 7 . The band at 740 nm can be attributed to the d–d transition of Cu 2+ , similar to Cu 2+ in compounds with weak crystal fields. − Further analysis about the charge-transfer band is discussed below. Besides, the absorption band at 510 nm may be caused by the unknown species of defect introduced by the doped Cu 2+ ions.…”

“…When increasing the temperature, this excitation peak shifts to a longer wavelength, as shown in Figure d, which is the primary feature of the charge-transfer band. By the way, the excitation peaks of the Cu 2+ d–d transitions are always located in the range from red to near infrared light. − …”

Comparative analysis of lanthanide excited state quenching by electronic energy and electron transfer processes

“…Indeed, the short distances found in this case ( R 0 between 2.8 to 4.4 Å for Mn 2+ quenching) fall within the range where the mechanism of energy transfer is collisional, operates over a short encounter distance and may involve the Dexter energy exchange mechanism 39 and not only Förster resonance energy transfer into the copper 2 T 2g orbital, which is more likely to operate with the aqua copper( ii ) ion. 40…”

Nanostructural Materials with Rare Earth Ions: Synthesis, Physicochemical Characterization, Modification and Applications

“…Conventional quantitative determinations of Ca 2+ concentration with ratio probes overcomes the dependence on local probe concentration by exploiting ratiometric procedures using excitation or detection at two wavelengths [59,60]. The advent of fluorescence lifetime imaging techniques [1,[61][62][63][64] opens new horizons for the quantitative determination for bio-imaging, in particular using intensity probes [65]. Fluorescence lifetime imaging is determined by factors such as the chemical environment of a fluorescent molecule and thus provides valuable information about its ion binding states.…”

“…The success of nanotechnology in the field of physical, chemical and medical sciences has started revolutionizing the drug delivery science and theranostics (therapy and diagnostics) [ 1 , 2 ]. The specific advantages include superior pharmacodynamics, pharmacokinetics, reduced toxicity and improved targeting capability.…”