1.8 μm luminescent properties and energy transfer of Yb3+/Tm3+ co-doped α-NaYF4 single crystals

• The Tm3+/Yb3+ co-doped α-NaYF4 single crystals were grown by Bridgman method.
• The 1.8 μm emission intensity is obtained at 15.38 mol% Yb3+/1.90 mol% Tm3+ sample.
• The maximum value of emission cross section at 1.8 μm is 1.63 × 10−20 cm2.
• The energy transfer rate is 1543 s−1 and energy transfer efficiency is 83.8%.
• The physical mechanism for energy transfer from Yb3+ to Tm3+ ions was analyzed.

This paper reports on successful preparation of α-NaYF4 single crystals co-doped with ∼1.9 mol% Tm3+ and various concentrations (3.85 mol%, 7.69 mol%, 11.54 mol%, 15.38 mol%) of Yb3+ by using a flux-Bridgman method. The fluorescence decay curve was measured to investigate the luminescent properties of the Yb3+/Tm3+ co-doped α-NaYF4, and the energy transfer process from Yb3+ to Tm3+; the J-O intensity parameters of Tm3+ were further calculated and analyzed according to the absorption spectra. Results show that, an intense 1.8 μm emission was achieved with Yb3+ as sensitizer for Tm3+ in the α-NaYF4 single crystal under the excitation of 980 nm LD (Laser Diode) because of the strong energy transfer from Yb3+ to Tm3+. The maximum emission intensity at 1.8 μm is obtained at about 15.38 mol% doping concentration of Yb3+ when the concentration of Tm3+ ions is fixed at ∼1.90 mol% in the current research. Moreover, the calculated maximum value of emission cross section at 1.8 μm is 1.63 × 10−20 cm2 for 3.85 mol% Yb3+/1.9 mol% Tm3+ sample, and the obtained energy transfer rate (WET) and energy transfer efficiency (η) are 1543 s−1 and 83.8%, respectively. Our analysis of the fluorescence dynamics indicates that electric dipole-dipole interaction is dominant for the energy transfer from Yb3+ ions to Tm3+ ions by using Inokuti-Hirayama’s model.