Upconversion and NIR persistent luminescence of CaTa4O11:Tb3+/Yb3+ phosphors prepared by molten salt synthesis

CaTa 4 O 11 (CTO):Tb 3+ /Yb 3+ phosphors were prepared using the molten salt synthesis. Under 980 nm laser excitation, this phosphor can emit light at 382 nm through a three-photon upconversion process from 5 D 3 → 7 F 6 in Tb 3+ . When the concentrations of Tb 3+ and Yb 3+ are 0.21 and 0.065, respectively, CTO:Tb 3+ /Yb 3+ exhibits the strongest upconversion green light emission from 5 D 4 → 7 F 5 in Tb 3+ , whose integral intensity is 5.77 times that of NaY(WO 4 ) 2 :Tb 3+ /Yb 3+ . Under 264 nm excitation, CTO:Tb 3+ /Yb 3+ has persistent 974 nm luminescence from 2 F 5/2 → 2 F 7/2 in Yb 3+ . By comparing the CTO host, CTO:Yb 3+ , CTO:Tb 3+ and CTO:Tb 3+ /Yb 3+ , the Ta 5+ -O 2- , Yb 3+ -O 2- and Tb 3+ -O 2- charge transfer bands (CTB) have been determined. During the downshifting process, Tb 3+ -O 2- CTB transfers energy to Yb 3+ -O 2- CTB. The trap depths of CTO:Yb 3+ and CTO:Tb 3+ /Yb 3+ are 0.680 and 0.679 eV, respectively, and their persistent times are 14.61 and 11.07 s, respectively. Under 980 nm laser excitation, the absolute and relative temperature sensitivities were obtained to be 2.74 and 0.178 K −1 , respectively. All results confirm that the CTO:Tb 3+ /Yb 3+ phosphors can be used as temperature sensing and infrared persistent luminescence.