Zhang Jiazhong

不同掺杂浓度Tm 3+ ：LiLuF 4 单晶的1800 nm荧光发射

LiLuF4 single crystals doped with molar fractions of 0.45%, 0.90%, 1.63%, and 3.25% (x, molar fraction) Tm3+ ions were fabricated by an improved Bridgman method. Absorption spectra in the 400-2000 nm region of the crystals were measured. The emissions from 1400 to 2000 nm under excitation of an 808-nm laser diode (LD) were carried out and compared. Two emission bands at 1470 and 1800 nm were observed. First, the emission intensity at 1800 nm increased with the increase in Tm3+ concentration, reaching a maximum value when the Tm3+ concentration was ca 0.90%. Thereafter, it decreased considerably as the Tm3+ doping levels further increased to 3.25%. However, the emission intensity at 1470 nm showed the contrary tendency to that at 1800 nm. It was found that the 1800-nm emission lifetime of the Tm3+:F-3(4) manifold systematically decreased with an increase in Tm3+ concentration. The trend in the fluorescent intensity change can be explained by the cross-relaxation (H-3(6), H-3(4)-> F-3(4), F-3(4)) between the Tm3+ ions and the concentration quenching effect of Tm3+. Meanwhile, the emission cross-section was calculated, providing a maximum of 0.392x10(-20) cm(2) at 1890 nm for the 0.90% doped sample. Based on the measured lifetime and calculated radiative lifetime, the largest quantum efficiency between Tm3+ ions reached similar to 120%.

2.0-μm emission and energy transfer of Ho3+/Yb3+ co-doped LiYF4 single crystal excited by 980 nm*

Ho3+/Yb3+ co-doped LiYF4 single crystals with various Yb3+ concentrations and ~ 0.98 mol% Ho3+ concentration are grown by the Bridgman method under the conditions of taking LiF and YF3 as raw materials and a temperature gradient (40 °C/cm–50 °C/cm) for the solid–liquid interface. The luminescent performances of the crystals are investigated through emission spectra, infrared transmittance spectrum, emission cross section, and decay curves under excitation by 980 nm. Compared with the Ho3+ single-doped LiYF4 crystal, the Ho3+/Yb3+ co-doped LiYF4 single crystal has an obviously enhanced emission band from 1850 nm to 2150 nm observed when excited by a 980-nm diode laser. The energy transfer from Yb3+ to Ho3+ and the optimum fluorescence emission around 2.0 μm of Ho3+ ions are investigated. The maximum emission cross section of the above sample at 2.0 μm is calculated to be 1.08×10−20 cm2 for the LiYF4 single crystal of 1-mol% Ho3+ and 6-mol% Yb3+ according to the measured absorption spectrum. The high energy transfer efficiency of 88.9% from Yb3+ to Ho3+ ion in the sample co-doped by Ho3+ (1 mol%) and Yb3+ (8 mol%) demonstrates that the Yb3+ ions can efficiently sensitize the Ho3+ ions.