Enhanced near infrared persistent luminescence of Zn2Ga2.98Ge0.75O8:Cr0.023+ nanoparticles by partial substitution of Ge4+ by Sn4+

Abstract

Spinel-phase Zn₂Ga_2.98Ge_0.75–xSn_xO₈:Cr_0.02³⁺ (ZGGSO:Cr³⁺) nanoparticles with various Sn⁴⁺ concentrations were prepared by a hydrothermal method in combination with a post-annealing in vacuum at high temperature. For these nanoparticles, the observed near infrared (NIR) persistent luminescence peaked at ∼697 nm and originates from the ²E, ⁴T₂ (⁴F) → ⁴A₂ transitions of Cr³⁺ and the afterglow time exceeds 800 min. For both the interior and surface Cr³⁺ ions in the ZGGSO host, it can be found that the increased energy transfer from Cr³⁺ to the deep trap (anti-site defects, ) after the substitution of Ge⁴⁺ by Sn⁴⁺ plays a key role in enhancing the persistent luminescence of the ZGGSO:Cr³⁺ nanoparticles. Strikingly, this energy transfer process can be controlled through the variations in the crystal field strength and the trap depths. Our results suggest that not only Sn⁴⁺ substitution can improve in vivo bioimaging but also the existence of deep traps in ZGGSO:Cr³⁺ nanoparticles is helpful for retracing in vivo bioimaging at any time.