Low-dose X-ray induced long afterglow NIR luminescence from Cr3+ doped Zn1–xCdxGa2O4 spinel solid solutions

The low-dose X-ray induced long afterglow near infrared (NIR) luminescence from Cr³⁺ doped Zn_1–xCd_xGa₂O₄ spinel solid solutions was investigated. The structure analysis shows the good formation of Zn_1–xCd_xGa₂O₄ spinel solid solutions, which possesses a cubic spinel structure with Fd3m space group. The formation of Zn_1–xCd_xGa₂O₄ spinel solid solutions induces the obvious increase of long afterglow near infrared luminescence excited by low-dose X-ray. When the content of doped Cd²⁺ reaches 0.1, the low-dose X-ray induced long afterglow NIR luminescence is the maximum. More importantly, only 5 s X-ray irradiation can induce more than 6 h NIR afterglow emission, of which the afterglow luminescent intensity is still 5 times stronger than the background intensity after 6 h. The thermoluminescent results show that under the 5 s exposure of X-ray, the trap density of Zn_0.9Cd_0.1Ga₂O₄:Cr³⁺ is much higher than that of ZnGa₂O₄:Cr³⁺. The replacement of Cd²⁺ ions with large radius at Zn²⁺ sites causes the increase of defects and dislocations, which results in the obvious increase of trap concentrations. And the addition of high-z number elements Cd²⁺ would enhance the X-ray absorption of the solid solutions, which thus can be easily excited by low-dose X-ray. Zn_0.9Cd_0.1Ga₂O₄:1%Cr³⁺ solid solution is a potential candidate of low-dose X-ray induced long afterglow luminescent materials.