Dye Sensitized Blue to UV-B Upconversion for Potential Light Therapy Applications

Abstract

UV-B light (311-313 nm) has been proven to treat skin disorders such as psoriasis and vitiligo[1][2][3]. Lanthanide ion doped phosphors are among the best for UC [4]and have been well studied for the IR-to-NIR[5] and NIR-to-Visible/UV processes[6][7]. Blue(⁓450nm) to UVB (⁓313nm) UC is a promising phototherapy method combining safer blue irradiation and topical UV-B light treatment which is beneficial for the patients. In this study, successful blue-to-UVB UC (⁓450nm to ⁓313nm) was realized in Ho3+/Gd3+ co-doped NaYF4 NPs; where the concentrations of Ho3+ and Gd3+ dopants were optimized to 1% and 25% respectively, with respect to the Y3+ lattice site. Due to the weak absorption of intra-4f transitions of Ho3+, organic Dye molecules (super-broad blue absorption), are utilized as Förster Resonance Energy Transfer (FRET) sensitization antennas on the surface of NaYF4:Ho3+/Gd3+ NPs through two binding strategies. Two kinds of Dye molecules, i.e., Perylene Propionic Acid (PPA2) and Commercial Coumarin (CC), were used to explore the binding procedures by altering the mass ratio of Dye molecules over NPs from 1:300, to 1:200, and to 1:100. It was observed that the UC intensity for a hybrid nanomaterial was enhanced relatively to bare NaYF4:Ho3+/Gd3+ NPs. Amongst the mass ratios 1:100 exhibits the most optimal blue-to-UVB UC efficiency. In addition, proofs of the efficient sensitization of Dye antenna was acquired by the time-resolved spectra, the overlap of excitation and absorption spectra of bare NPs, free Dye molecules and the hybrid nanomaterials.