Photoconductivity of CaGa ₂ S ₄ single crystals doped with Eu ²⁺ and Ce ³⁺

Abstract

CaGa 2 S 4 compounds doped with rare-earth elements (REE) exhibit luminescence with various colors. The emission process between the transition levels of REE ions has ever been extensively studied. We have measured the photoconductivity (PC) to confirm the locations of the 4f ground levels of the Eu 2+ and Ce 3+ions in the band gap of the host compounds of CaGa 2 S 4 for the first time.

Photoconductivity and thermally stimulated current in CaGa2S4 single crystals doped with Eu2+ and Ce3+

“…On the other hand, low temperature PC measurement was successfully carried out for a sample doped with 1 mol% Ce 3+ . Figure 2 shows its PC spectra at both 300 K and 26 K. The spectrum at 300 K has two peaks at 2.7 and 3.1 eV similar to those obtained previously [11]. In comwww.pss-a.com parison to the previous result, these peaks greatly differ in shape and even a little in energy position.…”

“…TSC was measured as a change in voltage across a series resistance by applying a voltage of 30 V while temperature was increased at a constant rate between 15 K/min and 20 K/min. Figure 1 shows PC spectra of CaGa 2 S 4 doped with 1 mol% Eu 2+ where the sample has better crystal quality than the previous one [11], giving a shoulder at 2.3 eV and peaks at 2.6 eV and 3.2 eV, which are almost the same but appear much clearer than those previously reported. Using this sample, a low temperature PC measurement was tried.…”

“…We have also found traps which may have repelling potential barriers. problem concerning the size and quality of the bulk crystals used [11].…”

“…It showed only a broad PC response that might mainly reflect the grain boundary defects. In our previous paper [11], we reported PC spectra showing the intrinsic information of a crystalline compound. However we could not still determine precisely the electronic energy levels of Ce ions because of the less distinct nature presumably ascribed to the bad crystal quality.…”

Enhancement of Mn red emission in CaGa2S4 compounds by co-doping rare-earth elements

“…Up to now, several studies have been carried out on strontium and calcium thiogallates doped with lanthanides [1][2][3][4][5][6][7][8][9][10][11]. However, for the above purpose , the luminescence efficiency of compounds should be increased in comparison to materials currently used in phosphor lamps and flat display panels.…”