In this work, the uniform bundle-shaped microtubes composed of six half-pipes are synthesized for the first time in hydrothermal solutions via an intentional delayed phase transition pathway induced by Mn(2+) doping. The structural and kinetic factors that govern the phase and shape evolution of NaYF4 microcrystals have been carefully studied, and the influences of Mn(2+) to RE(3+) ratio, the amount of trisodium citrate, and the pH value in conjunction with the intrinsic character of RE(3+) ions on the phase and shape evolution are systematically discussed. It is found that the proper Mn(2+) to RE(3+) ratio is mainly responsible for delayed phase transition process and induces interior density gradient of solid aggregate for creating hollow bundle-shaped microtubes. While the amount of trisodium citrate and the pH value are the keys for the shape control of the NaYF4 microcrystals such as prismatic microtubes, prismatic short rods, thin plates, and particles. The up and downconversion emissions were obtained independent of whether α- or β-NaYF4:Er(3+)/Yb(3+) samples doped with Mn(2+), but the significant tuning of output color was only obtained in cube NaYF4 nanoparticles rather than in hexagonal microtubes via adjusting the amount of Mn(2+) ions. These spectral measurements and EDX analyses indicate that the distribution or concentration of Mn(2+) in hexagonal phase solid solution has changed, which supports Ostwald ripening growth mechanism and rules out agglomeration or oriented attachment growth mechanism. We designed crystal growth mode by simply addition of dopant may provide a versatile approach for fabricating a wide range of hollow nano/microcrystals and thus bring us a clearer understanding on the interaction between the dopant reagents and the nano/microcrystals.
Efficient spectral conversion of 325–550 nm light to 570–710 nm light has been demonstrated in LaOF:Eu3+ nanocrystals. When levels above the D50 level of Eu3+ are optically excited, strong emission arising from the D50 level is obtained in the range of 570–710 nm, a highly efficient working range for organic solar cells. The influences of ambient temperature, particle size, dopant concentration, and codoped ions on the fluorescence intensity of Eu3+ are discussed in detail. The photon conversion efficiency can reach 3.91% in LaOF:Eu3+ codoped with Tm3+, if light reflection and scattering effects are ignored
Rod-shaped and plate-shaped NaYF4:Yb3+/Er3+ nanocrystals (NCs) have been synthesized via a facile oleic acid-assisted hydrothermal route. The intensity and color tunability by shape controlling of NCs is demonstrated by up and down frequency conversions in NaYF4:Yb3+/Er3+ NCs. The results obviously show that rod-shaped NCs present much stronger upconversion luminescence intensity and smaller ratio of green to red emission intensity than that of plate-shaped NCs. The underlying reason of luminescence enhancement by shape controlling is explored, and a mechanism of the enhancement based on the decrease of nonradiation relaxation probability and the increase of energy transfer efficiency from Yb3+ to Er3+ is proposed for nanorods.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations –citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.