Ultraviolet emissions from Gd3+ ions excited by energy transfer from Ho3+ ions

Abstract

Abstract Ultraviolet (UV) upconversion (UC) emissions of Gd 3+ ion were investigated in Y 1.838− x Gd x Yb 0.16 Ho 0.002 O 3 ( x =0, 0.16, 0.4, 1, 1.4) bulk ceramics under 976 nm laser diode (LD) excitation. The UC emissions centered at 309 and 315 nm are assigned to the transition of 6 P 5/2 → 8 S 7/2 (Gd) and 6 P 7/2 → 8 S 7/2 (Gd). The 6 P J levels of Gd 3+ ions are populated by an energy transfer (ET) process from 8 S 7/2 (Gd)+( 3 P 1 , 3 L 8 , 3 M 10 ) (Ho)→ 6 P J (Gd)+ 5 I 8 (Ho). A four-photon ET UC process was confirmed by the dependence of the 6 P 7/2 level emission intensity on the pumping power. We found that the intensity of the UC emissions increased with Gd 3+ ion concentration and peaked at 8 mol%, then starts to decrease until the Gd 3+ ion concentration reached 70 mol%. The variation in the UV emission intensity is the result of the competition between the ET process and concentration quenching effect. Theoretical calculations based on steady-state equations validated the proposed UC mechanisms.