White-Emitting Dy³⁺/Eu³⁺ Co-Doped Fluorapatite Nanoparticles for Multispectral Biomedical Applications

Engineering luminescent nanomaterials capable of emitting stable multispectral visible light remains a key challenge in the development of advanced bioimaging technologies. While white-light emission from rare-earth co-doped phosphors has been widely explored, most existing systems rely on multi-component architectures, high-temperature synthesis routes, or host matrices with limited biocompatibility, restricting their applicability in biomedical environments. Achieving multispectral emission within a single, biocompatible, and structurally stable host therefore remains an open challenge.

In this work, a simple and low-energy room-temperature co-precipitation route (≈25 °C) is reported for the synthesis of spherical Dy³⁺/Eu³⁺ co-doped fluorapatite (Ca₅(PO₄)₃F) nanoparticles, establishing fluorapatite as an efficient single-host platform for multispectral emission. Owing to its intrinsic biocompatibility and structural flexibility, fluorapatite enables the simultaneous incorporation of multiple rare-earth ions without compromising phase purity or crystallographic integrity. Structural characterization confirms successful Dy³⁺ and Eu³⁺ substitution within the apatite lattice, while FESEM analysis reveals uniformly distributed spherical nanocrystalline particles.

Under near-UV excitation at 380 nm, the co-doped nanoparticles exhibit combined visible emission arising from the characteristic Dy³⁺ blue/yellow transitions and Eu³⁺ red emission, resulting in an overall white-light appearance. This combined multispectral emission enables the collection of spectral signals from multiple regions of the visible spectrum using a single nanomaterial, which is particularly advantageous for multispectral bioimaging and multiplexed detection. Importantly, this multispectral luminescence is achieved using a single excitation wavelength and a single biocompatible host matrix, eliminating the need for hybrid or multi-phase phosphor systems and reducing spectral cross-talk.

The combination of room-temperature synthesis, intrinsic biocompatibility, spherical morphology, and single-host multispectral emission positions Dy³⁺/Eu³⁺ co-doped fluorapatite nanoparticles as a versatile platform for multispectral biomedical imaging and related applications requiring stable luminescent probes.