Preparation and characterization of stable aqueous suspensions of up-converting Er3+/Yb3+-doped LiNbO3 nanocrystals

Abstract

The preparation of LiNb03:Er 3+ /Yb 3+ nanocrystals and their up-conversion properties have been studied. It is demonstrated that polyethyleneimine-(PEÍ) assisted dispersión procedures allow obtaining stable aqueous LiNbÜ3 :Er 3+ /Yb 3+ powder suspensions, with average size particles well below the micron range (100-200 nm) and the isoelectric point of the suspensión reaching valúes well above pH 7. After excitation of Yb 3+ ions at a wavelengfh of 980 nm, the suspensions exhibit efflcient, and stable, IRto-visible (green and red) up-conversion properties, easily observed by the naked eye, very similar to those of the starting crystalline bulk material.

Bottom-up synthesis of up-converting submicron-sized Er3+-doped LiNbO3 particles

“…The red emission band, centered at around l w670 nm, is associated to the 4 F 9/2 / 4 I 15/2 transition while the green one is due to the radiative decay from the thermally coupled manifolds, 2 H 11/2 and 4 S 3/2 , to the ground state (l w 525 nm and l w 551 nm, respectively). Both emission bands are energetically coincident with those reported for other Er 3þ -doped LiNbO 3 samples [35] and only slight differences in the relative peak intensities associated to the emissions from the 2 H 11/2 and 4 S 3/2 manifolds are detected. Such kind of differences have been previously observed in other sub-micron sized particles and they can be attributed to a heating effect due to the presence of the IR-pumping beam [35].…”

“…Both emission bands are energetically coincident with those reported for other Er 3þ -doped LiNbO 3 samples [35] and only slight differences in the relative peak intensities associated to the emissions from the 2 H 11/2 and 4 S 3/2 manifolds are detected. Such kind of differences have been previously observed in other sub-micron sized particles and they can be attributed to a heating effect due to the presence of the IR-pumping beam [35]. In particular, it has been recently proved that this effect is useful to estimate the local temperature of the sample [36].…”

Temperature Sensing with Up-Converting Submicron-Sized LiNbO3:Er3+/Yb3+Particles

“…Apart from these differences, it has been verified that the overall emission characteristics, and particularly lifetimes, are not affected by the size reduction. 39) The great sensitivity to thermal effects of the green emissions makes the particles a very attractive local temperature probe using the FIR technique. Nevertheless, it also dictates some conditions, such as the power dependent heating caused by laser excitation.…”