Efficient up-conversion red emission from TiO_2:Yb,Er nanocrystals

Abstract

Usually, up-conversion (UC) green emission is easily observed by using rare-earth doped fluoride nanocrystals. However, preferential red emission is desired for some actual applications especially in biological field. Here, we demonstrated that the dominant UC red emission can be realized by preparing TiO:Yb,Er nanocrystals under 980 nm exciation. By controlling the crystal symmetry and size via the annealing temperature and Yb ions concentration, the enhanced UC red emission is achieved. The multi-photon relaxation and cross-relaxation mechanisms may be responsible for the energy transform process and in turn the UC emission.

Near-infrared to visible and ultraviolet upconversion in TiO2 thin films modified with Er and Yb

“…6a–c ), it was observed that the addition of a high concentration of Yb ions significantly increases intensity of the upconversion emission. It occurs due to the following probable mechanisms 45 (schematic diagram of UC processes shown in Fig. 6e ):…”

Red Upconverter Nanocrystals Functionalized with Verteporfin for Photodynamic Therapy Triggered by Upconversion

“…The evaluation of upconversion properties, upon excitation at 980 nm, evidenced that mostly red emission of Er 3+ is generated by upconversion, whilst the intensity of green emission is almost negligible. This aspect is very interesting because red upconversion luminescence is particularly desirable in biological and biomedical applications, but usually, whilst green upconversion is readily obtained in rare-earth doped crystals containing Er 3+ as the acceptor ion, additional doping or thermal annealing treatments are often needed to increase red upconversion [31,44].…”

“…One of the most used UC pairs is represented by Yb 3+ -Er 3+ , where the green and red emissions of Er 3+ are obtained through UC mechanism. However, preferential red emission, with respect to green, is desired for biological applications; therefore, most efforts have been focused on the development of UCNPs characterized by a strong and single-band red emission from the Yb-Er couple under the NIR irradiation [31]. Besides the dopants, the correct choice of the host matrix is fundamental, as it provides a platform for the energy transfer.…”

Synthesis of upconversion TiO2:Er3+-Yb3+ nanoparticles and deposition of thin films by spin coating technique

“…Although upconversion TiO 2 co-doped Er 3+ -Yb 3+ thin films have been already investigated by several research groups for different applications, the preparation of films with a good crystallinity, high surface area and efficient green and red luminescence at temperature below 500°C still remains challenging. Till know, the annealing temperature that has been used in most of the studies is above 500°C, in order to achieve high crystallinity and consequently an efficient luminescence [16], [20][21][22][23]. But, at high annealing temperatures: size, shape, phase and luminescence properties (specially the profile of the emissions) are changed.…”