Synthesis of new green emitting phosphors based on rare earth oxycarbonates

Abstract

New green emitting phosphors, hexagonal II-type Gd 2 O 2 CO 3 :Tb 3+ and Y 2 O 2 CO 3 :Tb 3+ , were synthesized by the simple flux method and their luminescence properties were compared with that of II-La 2 O 2 CO 3 :Tb 3+ . Bright green emission was observed in each sample and their particle sizes were in submicron scale. The excitation spectrum consisted of a broad band and some sharp peaks, which were corresponding to the 4f-5d transition of Tb 3+ and 4f-4f transition of Gd 3+ and Tb 3+ , respectively. The excitation wavelength of the 4f-5d bands depends on the distance between Tb 3+ and O 2− , which affects the crystal field effect on the 5d levels of Tb 3+ . Among lanthanum, gadolinium, and yttrium oxycarbonates, Gd 2 O 2 CO 3 is the most suitable host to obtain high emission intensity and the maximum intensity was obtained at the composition of Gd 2 O 2 CO 3 :17 at.% Tb 3+ , where it was 101% of that of a commercial LaPO 4 :Ce 3+ ,Tb 3+ phosphor.

Enhancement of the luminescent intensity of the green emitting Gd2O2CO3:Tb phosphor

“…These phosphors exhibited a wellknown characteristic of the Tb 3+ emission, and no self-activated emission was observed in the Tb 3+ -undoped Gd 2 O 2 CO 3 sample. The excitation spectra of the samples consist of strong broad bands around 260 nm, which can be attributed to the energy transition from 4f 8 to 4f 7 5d 1 configuration of Tb 3+ [11], as discussed in our previous papers [8,9]. The relative emission intensities compared with the commercial LaPO 4 :Ce 3+ ,Tb 3+ phosphor were 107.6, 110.4, and 110.0% for the Gd 2 O 2 CO 3 :16 at.%Tb 3+ samples prepared at 873, 923, and 973 K, respectively.…”

“…In our previous studies [8,9], the upper limit of the heating temperature in the flux treatment process was 823 K when the oxycarbonate phosphors were prepared in a flow of 10%CO 2 -90%N 2 gas, and the highest relative emission intensity was 101% obtained for Gd 2 O 2 CO 3 :17 at.%Tb 3+ . In the present study, on the contrary, there has been an increase of about 10% in the emission intensity of the Gd 2 O 2 CO 3 :Tb 3+ phosphor by employing pure CO 2 (100%) instead of 10%CO 2 -90%N 2 .…”

“…The diffraction patterns of the samples calcined at 973 K or less were in good agreement with that of a single phase of the hexagonal rare earth oxycarbonate (type II) and no impurity peak was observed. Although a small amount of potassium (<1 mol%) was detected by the XRF analysis in the samples, the luminescent properties of the oxycarbonate phosphors are not affected by the nominal flux remained in the samples [6][7][8][9][10]. On the contrary, the XRD pattern of the sample calcined at 1023 K corresponded to that of cubic Gd 2 O 3 and the color became a tinge of brown, which suggests that a part of terbium ions exists in the tetravalent state.…”

“…3 presents the concentration dependence of the luminescent emission intensity on the terbium ion in the Gd 2 O 2 CO 3 :xTb 3+ phosphors prepared at 923 K, in which the value x was changed from 11.5 to 18.3 at.%. The result for the conventional samples prepared in 10%CO 2 -90%N 2 [8,9] is also depicted in the figure. The reproducibility of the data was very well and the deviation of each relative intensity value was quite small.…”

“…The Eu 3+ -or Tb 3+ -doped II-RE 2 O 2 CO 3 (RE = La, Gd, and Y) phosphors prepared by our flux method showed high emission intensities despite that the particle size was in a submicron scale [6][7][8][9][10]. In the series of the oxycarbonate phosphors examined, II-Gd 2 O 2 CO 3 :17 at.%Tb 3+ exhibited the highest relative emission intensity, which was 101% of that of a commercial LaPO 4 :Ce 3+ ,Tb 3+ phosphor [8,9]. In this study, we have optimized the synthesis process by replacing 10%CO 2 pure CO 2 (100%) and by adjusting the flux treatment temperature, in order to enhance the emission intensity of the II-Gd 2 O 2 CO 3 :Tb 3+ phosphor.…”