Study On The Up-conversion Green Light Properties In Ho³⁺/Yb³⁺/Ce³⁺-codoped LiTaO₃ Polycrystals

A series of LiTaO₃ polycrystals with various doping concentration were prepared by high-temperature solid method. The results of X-ray diffraction showed that there was no new phase appeared in LiTaO₃ polycrystals with various doping concentration. Combination of the results of X-ray diffraction and UV - visible spectra showed that the doped Ho³⁺, Yb³⁺ and Ce³⁺ ions were presented in the form of substitutional lattice in LiTaO₃, not presented in the lattice gap.The up-conversion emissions were investigated under diode laser excitation of 980 nm. The strong green up-conversion emission and weak red up-conversion emission were observed in LiTaO₃:Ho³⁺/Yb³⁺. Both of intensities of the green and red up-conversion emission increased with the concentration of Ho³⁺ and Yb³⁺ ions, however, the intensities of green and red emission were reduced by doping with higher concentration of Ho³⁺ and Yb³⁺ ions. It was found that tridoping with Ce³⁺ ions is an innovative route to increase the green up-conversion emission and simultaneously suppressed red up-conversion emission, thus, thus, the efficiency of single green luminescence was improved. X-ray diffraction gave evidence that LiTaO₃ polycrystals tridoping with Ce³⁺, Ho³⁺, Yb³⁺ ions is still rhombohedra. The up-conversion emission spectra of Ho³⁺/Yb³⁺/Ce³⁺:LiTao3 shown that the tridoping with Ce³⁺ ions resulted in the increase of green up-conversion emission and the decrease of the red up-conversion, and the green up-conversion emission increased with the Ce³⁺ ions and reached the maximum intensity at Ho³⁺/Yb³⁺:LiTaO₃ tri-doped with 15mol% Ce³⁺ ions. The enhancement of the green up-conversion emission is attributed to the cross relaxation 5F3 (Ho³⁺) + 2^F_5/2 (Ce³⁺)â†'5F4/5S2 (Ho³⁺) + 2^F_7/2 (Ce³⁺) and 5I7 (Ho³⁺) + 2^F_7/2 (Ce³⁺)â†'5I6 (Ho³⁺) + 2^F_5/2 (Ce³⁺). It is proposed that heavily tridoping with Ce³⁺ ions leaded to a new cross relaxation 5F5 (Ho³⁺) + 2^F_7/2 (Ce³⁺)â†'5F4/5S2 (Ho³⁺) + 2^F_5/2 (Ce³⁺), which contributes to a significant enhancement of green up-conversion emission and the luminescence quenching of the red up-conversion emission.