Suppression of photocatalysis and long-lasting luminescence in ZnGa₂O₄by Cr³⁺doping

Abstract

ZnGa 2 O 4 powder, synthesized by a solid state method, exhibit efficient photocatalytic activity for rhodamine B (RhB) degradation under mercury lamp illumination.However, the photocatalytic activity of ZnGa 2 O 4 was highly suppressed due to Cr 3+ ions doping. We discussed the mechanism of photocatalysis based on the photoluminescence properties of ZnGa 2 O 4 and ZnGa 2 O 4 :Cr 3+ , and the blue fluorescence lifetimes of host ZnGa 2 O 4 with different Cr 3+ concentrations were also measured. The results indicated that Cr 3+ ions doping are act as recombination centers, which can highly reduce the amount and lifetime of the electron-hole pairs and thus reduce the photocatalytic activity of ZnGa 2 O 4 . The thermoluminescence (TL) curves of ZnGa 2 O 4 and ZnGa 2 O 4 :Cr 3+ showed that the amount of trapped electrons/holes in ZnGa 2 O 4 is almost seven times higher than that of ZnGa 2 O 4 :Cr 3+ . The suppressed long-lasting luminescence intensity and photocatalytic activity of ZnGa 2 O 4 :Cr 3+ were supposed to come from the decrease of trapped electrons/holes and shortened lifetime of the electron-hole pairs. Possible mechanisms of long-lasting luminescence and photocatalysis of ZnGa 2 O 4 coupled with photoluminescence mechanisms of ZnGa 2 O 4 :Cr 3+ were also proposed.

Cr3+‐activated Li5Zn8Al5Ge9O36: A near‐infrared long‐afterglow phosphor

“…Obviously, LZAG is a native phosphor with a broadband purple‐blue emission ranging from 300 to 750 nm and centered at ~456 nm, which can be observed upon excitation at 258 nm. Similar results have been reported for other zinc‐containing compounds, such as ZnGa 2 O 4, Zn 2 GeO 4, Zn 3 Al 2 Ge 2 O 10, and M 2 ZnGeO 4 (M=Li, Na, K) . The broad emission can be attributed to the recombination of donors ( and ) and acceptors () which are intrinsic defects of the LZAG host generated during the high‐temperature solid‐state reaction process .…”

Recent advances and prospects of persistent luminescent materials as inner secondary self-luminous light source for photocatalytic applications

“…At last, it is worth noting that the MPLs could sometimes act as the photocatalysts by themselves if their persistent spectra have overlapped with the absorption range of the photocatalytic-toward materials (PTM). Attempts based on the MPLs have made for the H2 production or RhB degradation, such as Sr2MgSi2O7:Eu 2+ ,Dy 3+ [66], Sr4Al14O25:Eu,Dy,Bi [66], ZnGa2O4:Cr 3+ [197], ZnGa2O4 [310,325], ZnxGa2O3+x [342], Ga2O3:Cr 3+ ,In 2+ [364], Ga2O3:Cr 3+ ,Zn 2+ [365]. However, the photocatalytic efficiency of such MPLs taken alone is always lower than that under the corresponding MPL@PCM composites when there is no external light source to continuously provide the photon energy.…”

Synthesis and characterization of a ZnGa2O4:Cr3+-based aerogel

“…As the calcination temperature increases, the luminescence intensity increases and the photocatalytic efficiency decreases. 27…”