Enhanced near infrared persistent luminescence of Zn(2)Ga(2.98)Ge(0.75)O(8):Cr(0.02)(3+) nanoparticles by partial substitution of Ge(4+) by Sn(4+)

Spinel-phase Zn(2)Ga(2.98)Ge(0.75–x)Sn(x)O(8):Cr(0.02)(3+) (ZGGSO:Cr(3+)) nanoparticles with various Sn(4+) 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 (2)E, (4)T(2) ((4)F) → (4)A(2) transitions of Cr(3+) and the afterglow time exceeds 800 min. For both the interior and surface Cr(3+) ions in the ZGGSO host, it can be found that the increased energy transfer from Cr(3+) to the deep trap (anti-site defects, [Image: see text]) after the substitution of Ge(4+) by Sn(4+) plays a key role in enhancing the persistent luminescence of the ZGGSO:Cr(3+) 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 Sn(4+) substitution can improve in vivo bioimaging but also the existence of deep traps in ZGGSO:Cr(3+) nanoparticles is helpful for retracing in vivo bioimaging at any time.