Hydrothermal synthesis and luminescence properties of octahedral LiYbF4: Er3+ microcrystals

Graphical abstract: LiYbF4: Er3+ octahedral microcrystals have been successfully prepared through a facile hydrothermal method assisted with EDTA. SEM, HRTEM, RD, PL spectra are used to characterize the samples. It can be seen from SEM data that the complexing agent EDTA made to hydrothermal synthetic procedures result in formation of LiYbF4 octahedral microparticles with smooth surface. From the HRTEM images, the distances between the lattice fringes were measured to be 2.99 A and 2.57 A which correspond to the d-spacing for (1 1 2) and (2 0 0) planes, respectively. From the XRD patterns for the LiYb0.99Er0.01F4 in the absence of chelating agent EDTA and in the presence of EDTA, it is evident that the diffraction peaks of both patterns are highly crystalline and all of the peaks could be readily indexed to the LiYbF4 phase (JCPDS 71-1211). No other impurity peaks were detected. Under 976 nm excitation, the upconversion (UC) luminescence emission spectra of LiYbF4: Er3+ microcrystals show the characteristic Er3+ emissions. The results show that the infrared light emissions at 792 nm of 4I9/2 → 4I15/2 are dominantly strong unusually, while the green emissions at 526 and 545 nm assigned to 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2, respectively, and the red emission at 667 nm of 4F9/2 → 4I15/2 are relatively weaker. Research highlights: → Monodisperse and regular octahedral microcrystals LiYbF4: Er3+ with smooth surface has been prepared. → The characteristic emissions of Er3+ ions are observed in LiYbF4 microcrystals. → The content of EDTA will influence the fluorescence intensity. → Luminescence intensity increases gradually at the beginning and then decreases gradually with increasing temperature. -- Abstract: LiYbF4: Er3+ octahedral microcrystals have been successfully prepared through a facile hydrothermal method assisted with EDTA (ethylenediaminetetraacetic acid). X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric and differential scanning calorimeters (TG-DSC), photoluminescence (PL) spectra are used to characterize the samples. Under 976 nm excitation, the upconversion (UC) luminescence emission spectra of LiYbF4: Er3+ microcrystals show the characteristic Er3+ emissions. The results show that the infrared light emissions at 792 nm of 4I9/2 → 4I15/2 are dominantly strong unusually, while the green emissions at 526 and 545 nm assigned to 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2, respectively, and the red emission at 667 nm of 4F9/2→4I15/2 are relatively weaker. Most importantly, the samples show more efficient luminescence with further heat treatment.