Fluoride is one of the elements commonly present in the human environment. Due to its characteristics, it is very widely used in medicine, dentistry, industry or agriculture. On the other hand, its universality possesses a real threat to the human body in the form of acute and chronic poisoning. The aim of this paper is to characterize the properties of fluoride and its effects on the human body, as well as the sources of its occurrence. Particular emphasis is placed on the safety of its use and optimal dosage intake, which prevents accumulation and reduces its potential side effects. The positive effect of proper fluoride supply is widely described. In order to avoid overdose, it is best to consult a specialist to properly select the dosage.

The β-KYP₂O₇ powders doped with Sm³⁺, Tb³⁺ and Dy³⁺ were obtained using a one-step urea-assisted combustion method. Their structural properties were characterized by X-ray diffraction (XRD) whereas spectroscopic properties like excitation, emission and luminescence kinetics were investigated at room temperature. β-KYP₂O₇ doped with Sm³⁺ and Dy³⁺ showed concentration quenching above 2 mol% of dopants whereas Tb³⁺ containing materials could be doped with higher concentrations. The main mechanisms of concentration quenching were identified as dipole–dipole for Sm³⁺ and Dy³⁺. Both dopants due to the abundant energy levels are strongly prone to quenching due to the non-radiative CR process whose efficiency strongly increases with the concentration of optically active ions. In the case of Tb³⁺ emission from both ⁵D₃ and ⁵D₄ levels was recorded. The ⁵D₃ level vastly depopulates due to the CR process upon increase of the Tb³⁺ content whereas the slight ⁵D₄ emission remains stable up to 5 mol%.

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 C_s 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.