Effect of lanthanide doping on crystal phase and near-infrared to near-infrared upconversion emission of Tm3+ doped KF–YbF3 nanocrystals

Abstract Tm 3+ doped KF–YbF 3 nanocrystals were synthesized by a hydrothermal method using oleic acid as a stabilizing agent at 190 °C. The influence of Gd 3+ and Sm 3+ content on the phase structure and upconversion (UC) emission of the final products was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UC spectra. XRD analyses and TEM observations evidence that the phase and size of the as prepared Tm 3+ doped KF–YbF 3 nanocrystals are closely related to the Gd 3+ doping content. Without Gd 3+ impurity, the undoped nanocrystals crystallize in orthorhombic KYb 2 F 7 with an average diameter of 42 nm. When the Gd 3+ doping is below 10 mol%, the orthorhombic KYb 2 F 7 nanocrystals grow up. However, with Gd 3+ addition beyond about 30 mol%, the complete phase transformation from orthorhombic KYb 2 F 7 to cubic KGdF 4 occurs in the final products. Under the excitation of a 980 nm laser diode, the as prepared Tm 3+ doped nanocrystals exhibit strong near-infrared UC emission at 800 nm. Particularly, the intensity of high energy UV and blue UC emissions of Tm 3+ ions in Tm 3+ doped KYb 2 F 7 nanocrystals are selectively reduced compared to the NIR emission at 800 nm by co-doping a small amount of Sm 3+ ions into the host matrix. Possible dynamic processes for UC emissions in Tm 3+ doped nanocrystals are discussed in detail.