Fluorescence quantum yield of Gd0.9?xRxEu0.1OOH (R=Y, La) crystals

Gd0.9–xxRxEu0.1OOH (R=Y, La) crystals were synthesized by a flux method using a mixture of NaOH and KOH as the flux. X-ray diffraction data were well refined using the Rietveld method assuming that the crystals had a monoclinic structure belonging to the P21/m space group. The unit cell volumes of the Gd0.9–xxLaxEu0.1OOH crystals increased with increasing x, whereas those of Gd0.9–xxYxEu0.1OOH decreased with increasing x. The Commission Internationale de I'Eclairage (CIE) chromaticity coordinates of Gd0.9–xxRxEu0.1OOH (R=Y, La) crystals were located in the red region and were nearly constant over the range of x values considered. The fluorescence quantum yieldϕf monotonically decreased with increasing x regardless of the ionic radii of the substitute ions. The fact that the ϕf value of La0.9Eu0.1OOH was greater than that of Gd0.9Eu0.1OOH indicated that the observed decrease in the ϕf values of the Gd0.9–xxLaxEu0.1OOH crystals up to x=0.3 could not be attributed to an increase in the distance between Eu3+ ions or to a decrease in the Gd3+ content. The decrease might be due to an increase of killer centers introduced by elemental substitutions with the larger ion.

Graphical AbstractPhotographs of as-grown crystals synthesized by a flux method (a) Gd0.9Eu0.1OOH (x= 0), (b) Gd0.85Y0.05Eu0.1OOH, and (c) Gd0.85La0.05Eu0.1OOHFigure optionsDownload as PowerPoint slide