Luminescence Centers in BaFCl:Ce^(3+) and BaFCl:Gd^(3+) Crystals

Introduction In BaFCl crystal which is of PbFCl type structure in tetragonal system, Ba;ions situate at sites of C;point symmetry, while F;and Cl;ions occupy sites of D;and C;symmetry, respectively. The rare earth ions RE;doped in BaFCl should randomly replace the sites of Ba;ions, and their extra positive charges may be compensated by

LUMINESCENCE CENTERS OF Eu^(2+) IN KCaF_3:Eu^(2+)

The nature of the emission center of Eu^(2+) in KCaF_3:Eu^(2+) strongly depends on the preparative condi- tions.Experimental results show that there are two different d→f transition emission bands,and the origin of these two emission bands,their interrelationship and the effect of doping concentration on them have been dis- cussed.A Eu^(2+)-Eu^(3+) valency change process has been proposed.

Generation of color-controllable room-temperature phosphorescence via luminescent center engineering and in-situ immobilization

Materials with controllable luminescence colors are highly desirable for numerous promising applications, however, the preparation of such materials, particularly with color-controllable room-temperature phosphorescence(RTP), remains a formidable challenge. In this work, we reported on a facile strategy to prepare color-controllable RTP materials via the pyrolysis of a mixture containing 1-(2-hydroxyethyl)-urea(H-urea) and boric acid(BA). By controlling the pyrolysis temperatures, the as-prepared materials exhibited ultralong RTP with emission colors ranging from cyan, green, to yellow. Further studies revealed that multiple luminescent centers formed from H-urea, which were in-situ embedded in the B2O3matrix(produced from BA) during the pyrolysis process. The contents of the different luminescent centers could be regulated by the pyrolysis temperatures, resulting in color-tunable RTP. Significantly, the luminescent center engineering and in-situ immobilization strategy not only provided a facile method for conveniently preparing color-controllable RTP materials, but also endowed the materials prepared at relatively lower temperatures with color-changeable RTP features under thermal stimulus. Considering their unique properties, the potential applications of the as-obtained materials for advanced anti-counterfeiting and information encryption were preliminarily demonstrated.

Studies on long lasting optical properties of Eu^(2+) and Dy^(3+) doped di-barium magnesium silicate phosphors

Di-barium magnesium silicate phosphors doped with europium and dysprosium were prepared under a weak reducing atmosphere.X-ray diffraction pattern of the sample was also done that confirmed the proper preparation of the phosphor.Scanning electron microscope（SEM） images confirmed that the sample has regular surface and uniform grain size distribution.Comparative studies of phosphorescence decay of Ba2MgSi2O7：Eu^2＋,Dy^3＋ phosphors with different concentration of Dy^3＋ were done.The phosphor with 0.5/1.5 mol%of Eu/Dy,exhibited optimum green color afterglow properties.This emission is expected to arise due to transition of Eu^2＋ ions from any of the sublevels of 4f^65d^1 configuration to ^8S（7/2） level of the 4f7 configuration.For a suitable trap depth,the trap concentration is expected to be proportional to the concentration of Dy^3＋.These traps are responsible for holding the charge career for a reasonable time,subsequently for increasing the time of afterglow.Hence,optimum Dy3＊ concentration produces the longer afterglow duration with higher intensity of luminescence signals.Trap depth were also calculated using thermoluminescence glow curve which was indicative of formation of traps suitable for long afterglow.