Lanthanide (Ln³⁺)–doped upconversion nanoparticles (UCNPs) offer an ennormous future for a broad range of biological applications over the conventional downconversion fluorescent probes such as organic dyes or quantum dots. Unfortunately, the efficiency of the anti−Stokes upconversion luminescence (UCL) process is typically much weaker than that of the Stokes downconversion emission. Albeit recent development in the synthesis of UCNPs, it is still a major challenge to produce a high−efficiency UCL, meeting the urgent need for practical applications of enhanced markers in biology. The poor quantum yield efficiency of UCL of UCNPs is mainly due to the fol-lowing reasons: (i) the low absorption coefficient of Ln³⁺ dopants, the specific Ln³⁺ used here being ytterbium (Yb³⁺), (ii) UCL quenching by high−energy oscillators due to surface defects, impurities, ligands, and solvent molecules, and (iii) the insufficient local excitation intensity in broad-field il-lumination to generate a highly efficient UCL. In order to tackle the problem of low absorption cross-section of Ln3+ ions, we first incorporate a new type of neodymium (Nd³⁺) sensitizer into UCNPs to promote their absorption cross-section at 793 nm. To minimize the UCL quenching induced by surface defects and surface ligands, the Nd³⁺-sensitized UCNPs are then coated with an inactive shell of NaYF₄. Finally, the excitation light intensity in the vicinity of UCNPs can be greatly enhanced using a waveguide grating structure thanks to the guided mode resonance. Through the synergy of these three approaches, we show that the UCL intensity of UCNPs can be boosted by a million−fold compared with conventional Yb³⁺–doped UCNPs.

ZnO doped with Eu³⁺ and Tb³⁺ had been successfully prepared by wet chemical method with the assistance of microwave. The influence of reaction conditions such as temperature, time, content of Eu³⁺, Tb³⁺ ion, and annealing treatment on the structure and luminescent characteristics was studied. The analysis of energy dispersive spectroscopy (EDS) and photoluminescence spectra measurements indicated that Eu³⁺ and Tb³⁺ exist in host lattice and create the new emission region compared to ZnO crystalline host lattice. The field emission scanning electron microscope (FE-SEM) studies show the Eu³⁺, Tb³⁺ doped ZnO nanoparticles have a pseudohexagonal shape. The particle size was 30–50 nm for ZnO:Eu³⁺ and 40–60 nm for ZnO:Tb³⁺. Photoluminescence excitation (PLE) and photoluminescence (PL) spectra at room temperature have been studied to recognize active centers for characteristic luminescence of ZnO:Eu³⁺ and ZnO:Tb³⁺. The characteristic luminescent lines of Eu³⁺ (⁵D₀-⁷F_j) and Tb³⁺ (⁵D₄-⁷F_j) were determined. It has been demonstrated that the wet chemical synthesis method with microwave assistance can strongly enhance the luminescent intensity of nanoparticles ZnO:Eu³⁺ in red and ZnO:Tb³⁺ in green.

Y₂O₃:Eu³⁺ nanophosphors were prepared through combustion reaction under controlled condition of the fuel ethylenediaminetetraacetic acid (EDTA‐Na₂) and in the temperature range from 350 to 700°C. The products were characterized by X‐ray diffraction (XRD), field emission scattering electron microscopy (FESEM), and energy dispersive spectroscopy (EDS). The results showed that Y₂O₃:Eu³⁺ nanoparticles were successfully synthesized by combustion method at low temperature and in short reaction time. The light‐emitting ability of Y₂O₃:Eu³⁺ nanoparticles upon the electron excitation has been studied at the potentials 5, 10, and 15 kV. The thermoluminescent glow curves have elucidated an intense peak at 117°C after UV exposure and at least two peaks at 125 and 336°C with Gamma irradiation. Photoluminescent spectra of Y₂O₃:Eu³⁺ nanoparticles exhibited strong red luminescent color with highest sharp band at 612 nm under excitation in ultraviolet at 254, 394 and in visible at 465 nm. The dependence of photoluminescent properties of Y₂O₃:Eu³⁺ nanoparticles on annealing temperature and concentration of Eu³⁺ was also studied.

We report on the synthesis and characterization of folic acid-conjugated silica-modified TbPO₄·H₂O nanorods for biomedical applications. The uniform shape TbPO₄·H₂O nanorods with a hexagonal phase were successfully synthesized by wet chemical methods. A novel TbPO₄·H₂O@silica-NH₂ nanocomplex was then formed by functionalizing these nanorods with silica and conjugating with biological agents. The field emission scanning electron microscopy, energy-dispersive X-ray, and X-ray diffraction reveal the morphology and structure of the nanorods, with their controllable sizes (500-800 nm in length and 50-80 nm in diameter). The Fourier transform infrared spectroscopy was employed to identify chemical substances or functional groups of the TbPO₄·H₂O@silica-NH₂ nanocomplex. The photoluminescence spectra show the four emission lines of TbPO₄·H₂O@silica-NH₂ in folic acid at 488, 540, 585, and 621 nm under 355 nm laser excitation, which could be attributed to the ⁵D₄-⁷ ( ) transitions of Tb³⁺. The TbPO₄·H₂O@silica-NH₂ nanorods were conjugated with folic acid for the detection of MCF7 breast cancer cells. The obtained results show a promising possibility for the recognition of living cells that is of crucial importance in biolabeling.