The UC fluorescence emission and tuning from Ce ³⁺ codoped β-NaY(Gd _0.4 )F ₄ :Yb ³⁺ /Ho ³⁺ nanocrystals.

Vibrational modes and tip enhanced Raman spectroscopy (TERS) of a new carbon allotrope, cyclo[18]carbon (C₁₈), were studied by density functional theory. A silver cluster tip was used to probe the interaction with C₁₈, which is dependent on the distance and the atomically resolved positions. The TERS images show the position of the CC bonds, as observed in a recent experimental report.

Rare earth ion-doped upconversion materials show great potential applications in optical and optoelectronic devices due to their novel optical properties. In this work, the NaYF₄:Yb³⁺/Ho³⁺ microrods have been successfully prepared by a hydrothermal method assisted with EDTA (ethylenediaminetetraacetic acid). Time controlled experiments were carried out and the growth mechanism of dissolution–recrystallization of the microrods is proposed. It is important that the unusual upconversion emission with a candy-like pattern from single NaYF₄:Yb³⁺/Ho³⁺ microrods can be detected by confocal microscopy under NIR 980 nm excitation. The influence of the particle number on the UC emission spectra and the overall luminescence color was investigated systematically. We noted that the multicolor emission from the single NaYF₄:Yb³⁺/Ho³⁺ microrods can be successfully obtained only by adjusting the excitation strength or the size of the microrods. The present study is of great importance for multicolor tuning of RE-doped NaYF₄ nano/micromaterials as well as for understanding the up-mechanism. In addition, the luminescence from single microparticles can provide more precise spectral information on three-dimensional displays and biological labels.

An innovative route to tune upconversion (UC) emission in β-NaYF₄:Yb³⁺/Tm³⁺ nanorods through codoping a third rare-earth ion upon continuous wave excitation near 976 nm is reported. The dependence of UC emission on codopant concentration and environment temperature shows that tailored local environment and readjustable depopulation of excited-state ions are responsible for the tuning of UC luminescence. Codopant ions introduce a new distribution of active ions and a modified distance between Tm³⁺ and Yb³⁺ ions, making UC systems more sensitive to impurity ions than downconversion systems.