Up-conversion luminescence of trivalent-rare-earth ion-doped LnTaO4 (Ln = Y, Gd, La)

The up-conversion luminescence properties of trivalent-rare-earth ion-doped orthotantalates are studied under 980 nm laser diode excitation. The results indicate that YTaO₄:Tm³⁺/Yb³⁺ emits blue and strong infrared emissions respectively corresponding to ¹G₄→³H₆ and ³H₄→³H₆ transitions of Tm³⁺ ions, while YTaO₄:Er³⁺/Yb³⁺ produces strong green and weak red emissions, resulting from ²H_11/2/⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 transitions of Er³⁺ ions, respectively. In contrast to three excellent up-conversion phosphors, viz. NaYF₄:Er³⁺/Yb³⁺, Y₂O₂S:Er³⁺/Yb³⁺ and Y₂O₃:Er³⁺, YTaO₄:Er³⁺/Yb³⁺ shows not only strong green emission, but also larger intensity ratio of green to red emission. In addition, it is found that LaTaO₄: Er³⁺/Yb³⁺ shows the minimum quenching concentration of Yb³⁺ and weakest up-conversion emission intensity, and the main peak presents blue shift (8 nm/556 nm) as compared with YTaO₄:Er³⁺/Yb³⁺ and GdTaO₄:Er³⁺/Yb³⁺. The distinct luminescent characteristics of LaTaO₄: Er³⁺/Yb³⁺ can be attributed to the larger difference of radius between doped ion and La³⁺ ion.