Upconversion Luminescence from Ho3+ and Yb3+ Codoped α-NaYF4 Single Crystals

Abstract

The Ho 3+ /Yb 3+ co-doped α-NaYF 4 single crystal was grown successfully for the first time by a modified Bridgman method in which KF was used as assisting flux and a large temperature gradient (70−90 • C/cm) of solid-liquid interface was adopted. Upconversion emissions at green ∼544 nm, red ∼657 and ∼751 nm were obtained under 980 nm laser diode excitation. The intensity at ∼544 nm was much stronger than those of ∼657 and ∼751 nm. The mechanisms of the upconversion emissions were investigated by studying the relationship between the upconversion intensity and pump power. The optimized Yb 3+ concentration was about 8.08mol% when Ho 3+ concentration was hold at about 1.0mol%. The results showed that Ho 3+ /Yb 3+ doped α-NaYF 4 single crystal was a possible candidate upconversion material for the green solid-state laser.

Upconversion luminescence and optical thermometry behaviors of Yb3+ and Ho3+ co-doped GYTO crystal

“…The green emission at approximately 550 nm and the red emission at 650 nm correspond to characteristic transitions of Ho 3+ : 5 F 4 / 5 S 2 → 5 I 8 and 5 F 5 → 5 I 8 , respectively [ 20 , 46 , 47 ]. Previous studies [ 23 , 26 ] have extensively investigated the phenomenon of concentration quenching in UC emission, primarily attributed to an excessive concentration of Yb 3+ . In these studies, it was shown that, when the concentration of Yb 3+ exceeds 10 at%, the concentration quenching becomes evident, leading to a significant decrease in UC emission.…”

“…Yb 3+ possesses unique features, including outstanding absorption at 980 nm and favorable energy levels matching with those of Ho 3+ ions, making it an excellent sensitizer [ 19 – 22 ]. The energy transfer mechanism between Yb 3+ and Ho 3+ in α -NaYF 4 with strong green emission and in core–shell β -NaYF 4 nanoparticles with red emission was investigated by Zhang et al [ 23 ] and Pilch et al [ 24 ]. Additionally, numerous UC luminescent matrices co-doped with Yb 3+ and Ho 3+ were thoroughly studied for their potential application in non-thermally coupled temperature sensors based on the LIR technique.…”