Fluorescence sensing mechanism of contaminant Cu2+ in water by up-converting nanoparticles - Puga, Ruben; Lopez-Pena, Gabriel; Ortiz, Elisa; Pinto, Alvaro; Troya, Gino; Loro, Hector; Sole, Jose Garcia; Lifante-Pedrola, Gines; Ortgies, Dirk H; de Cardenas, Laura Fernandez; Cantelar, Eugenio (Spectrochimica Acta Part A-Molecular And Biomolecular Spectroscopy, 2026)