Modulated single band red upconversion luminescence from Ho3+ doped nanoparticles with two-wavelength excitation

Single band red upconversion luminescence has the potential applications from science to engineering, however, suffered from low luminescence efficiency. Single band enhanced red upconversion luminescence from NaYF4: Ho nanoparticles has been realized with the modulation of two-wavelength excitation and the administration of cross relaxation between F-5(4), S-5(2) -> F-5(5) and I-5(7) -> I-5(6) of Ho3+. Compared to the sum intensities with single-wavelength excitation at 975 nm and 1150 nm, the upconversion intensity for red and green luminescence is enhanced by the factors of 13.04 and 0.46 respectively with two-wavelength excitation. The red/green ratio of upconversion luminescence intensity is modulated from 15.46 to 115.03 by controlling the interionic distance and cross relaxation between Ho3+ ions. The microscopy mechanism of single band enhanced red upconversion luminescence with two-wavelength excitation at 1150 nm and 975 nm is ascribed to the ground state absorption of 1150 nm and excited state absorption of 975 nm, which was explored by power depended upconversion luminescence intensities, excitation spectra, and absorption spectrum. Besides, single band red upconversion luminescence from NaYF4: 10% Ho nanoparticles with the two-wavelength excitation shows the comparable intensity with that from NaYF4: 20% Yb, 2% Ho nanoparticles excited by 975 nm. Our results might provide a new method for the single band red upconversion luminescence with the applications in biology and three-dimensional displays. (C) 2017 Published by Elsevier B.V.