RESUMEN
In our previous study, we have reported the cooperative luminescence of Yb3+-trimers and cooperatively sensitized Gd3+ luminescence by Yb3+-tetramers in a doped CaF2 host. In this study, we experimentally observed an unusual luminescent phenomenon of Gd3+ in CaF2:Yb3+/Gd3+. Upon excitation with a 980 nm laser, the upconversion luminescence of Gd3+ first increases and then decreases in the Gd3+ concentration range of 0-0.9 mol%; this is different from the monotonic increase of Gd3+ luminescence observed in the downconversion spectra via the direct excitation of Gd3+. This special luminescent behavior was indicated to be related to the energy transfer from the Yb3+-tetramers to Gd3+ and the destruction of Yb3+-clusters. Herein, we proposed a new luminescence quenching mechanism, Yb3+-cluster destructive quenching, which was verified by fluorescence dynamic analysis and an optically inactive rare-earth ion-doping experiment.
RESUMEN
White upconversion luminescence (UCL) was achieved under 980 nm excitation in the CaF2:Yb(3+)/Eu(3+) material using Y(3+) to adjust the luminescence performance. In this luminescent system, Yb(3+) not only plays the role of a sensitizer of Eu(3+), but also generates green fluorescence from Yb(3+) dimers (2-Yb(3+)) by cooperative transitions in the CaF2 matrix. One of the primary colors of green corresponds to the 2-Yb(3+) cooperative emission exactly. Eu(3+) acts as an activator for emitting red and blue fluorescence simultaneously. Interestingly, the color of the UCL can be controlled by adjusting the doping concentration of Y(3+) ions, and white UCL was realized when the concentration of Y(3+) was 1%.
RESUMEN
Na8Al6Si6O24Cl2 : Mn and Na8Al6Si6O24Cl2 : Fe NIR phosphors were prepared by a solid-solid reaction at high temperature. Their crystal structures of fluorescent powder were investigated by using X-ray powder diffraction (XRD), and their NIR emission spectrum and excitation spectrum were measured at room temperature. The main emission peak of Mn5+ in the Na8Al6Si6O24Cl2 : Mn phosphor was observed at 1 200 nm in the NIR spectral region under 400 or 602 nm excitation, attributing to the 3A2-3T2 and 3A2-1E transitions of Mn5+ ions. The characteristic NIR luminescence of Mn5+ in sodalite is greatly enhanced by co-doping manganese and sulfur. A mechanism of the energy transfer between S2(-) and Mn5+ was also proposed here. The main emission peak of Fe2+ ions in the Na8Al6Si6O24Cl2 : Fe phosphor was recorded at 1 000 nm in the NIR region under the excitation of 334 or 500 nm. This photoluminescence originated from the 3T1-5 E transition of Fe2+. Such an emission in the NIR region suggests a potential application in improving solar spectrum to enhance the efficiency of silicon solar cells.
