Effect of Ho3+ Substitution on Magnetic Properties of ZnCr2Se4.

A series of ZnCr2-xHoxSe4 microcrystalline spinels (where x = 0.05, 0.075, and 0.10) containing holmium ions in octahedral coordination were obtained by sintering of adequate reactants at high temperatures. The obtained doped materials were characterized by X-ray diffraction, Scanning Electron Microscopy, UV-Vis-NIR, molecular field approximation, and XPS spectroscopies. Their thermal properties were also investigated. The doping of the ZnCr2S4 matrix with paramagnetic Ho3+ ions with a content of not more than 0.1 and a screened 4f shell revealed a significant effect of orbital and Landau diamagnetism, a strong reduction in short-range ferromagnetic interactions, and a broadening and shift of the peak of the first critical field by simultaneous stabilization of the sharp peak in the second critical field. These results correlate well with FPLO calculations, which show that Cr sites have magnetic moments of 3.19 µB and Ho sites have significantly larger ones with a value of 3.95 µB. Zn has a negligible magnetic polarization of 0.02 µB, and Se induces a polarization of approximately -0.12 µB.

White light and near-infrared emissions of Pr3+ ions in SiO2-LaF3 sol-gel nano-glass-ceramics.

In this work, we report the results of our investigations on the structural and luminescence properties of SiO2-LaF3:Pr3+ nano-glass-ceramics synthesized using the sol-gel method. Based on XRD, microscopic (TEM), and ATR-IR measurements, the crystallization of LaF3 nanocrystals favorably occupied by Pr3+ ions and overall transformations within the silicate sol-gel hosts dependent on heat-treatment conditions of the as-prepared amorphous xerogels were characterized. The fabricated oxyfluoride nano-glass-ceramics revealed the emissions within the greenish-blue (3P0,1 → 3H4, 3P0,1 → 3H5), reddish-orange (3P0,1 → 3H6, 1D2 → 3H4, 3P0 → 3F2,3), and NIR spectral scopes (1D2 → 3F4,1G4, 1G4 → 3H5, 3F3,4 → 3H4). Based on the luminescence spectra in the VIS range, the CIE chromaticity coordinates, correlated color temperatures (CCT), and color purities (CP) were calculated. The obtained results clearly indicate that the prepared Pr3+-doped sol-gel nano-glass-ceramics exhibit warm or neutral white light emissions with CCT values in the range from 2567 K to 3962 K. The lowest CP value was estimated at 12.8%, indicating that the fabricated samples are able to emit bright white light. Additionally, the NIR emissions cover E, S, C, and L bands, which are important for devices applicable in telecommunication technologies. For further characterization, the τ(3P0) and τ(1D2) decay times were estimated. It was established that the emissions from the 3P0 and the 1D2 excited states of Pr3+ ions, as well as the participation of cross-relaxation (CR) processes, are dependent on the size of crystallized LaF3 phase, distribution of optically active Pr3+ ions between amorphous and crystalline phase (determining the Pr3+-Pr3+ inter-ionic distances), and relative content of OH groups in the prepared sol-gel hosts.