Enhanced emission at 2.85 μm of Ho3+/Pr3+ co-doped α-NaYF4 single crystal

The Ho³⁺/Pr³⁺ co-doped NaYF₄ single crystals with various Pr³⁺ concentrations and constant Ho³⁺ molar percentage of ~1% were grown by an improved Bridgman method. Compared with the Ho³⁺ single-doped NaYF₄ crystal, an obviously enhanced emission band at 2.85 μm is observed under 640 nm excitation. The Judd-Ofelt strength parameters (Ω ₂, Ω ₄ and Ω ₆) are calculated, the radiative transition probabilities (A), the fluorescence branching ratios (β) and the radiative lifetime (τ _rad) are obtained in the meantime. The energy transfer from Pr³⁺ to Ho³⁺ and the optimum fluorescence emission of Ho³⁺ ions around 2.85 μm are investigated. Moreover, the maximum emission cross section of above samples at 2.85 μm is calculated to be 0.72×10^-20 cm² for the NaYF4 single crystal with Ho³⁺ molar percentage of 1% and Pr³⁺ molar percentage of 0.5% according to the measured absorption spectrum. All results suggest that the Ho³⁺/Pr³⁺ co-doped NaYF₄ single crystal may have potential applications in mid-infrared lasers.     

The optical properties of Tm3+ doped Na5Lu9F32 single crystal

Tm3+ doped Na5Lu9F32 single crystal with high optical quality was grown by an improved Bridgman method. The Judd-Ofelt intensity parameters Ωt (t=2, 4, 6) were calculated according to the measured absorption spectra and physical-chemical properties of the obtained Na5Lu9F32 single crystal. The stimulated emission cross-section of the 3F4→3H6 transition (~1.8 μm) is 0.35×10-20 cm2 for Tm3+ doped Na5Lu9F32 single crystal. The emission spectra under the excitation of 790 nm laser diode (LD) and fluorescence lifetime at 1.8 μm were measured to reveal the fluorescence properties of Tm3+ doped Na5Lu9F32 single crystal. The research results show that the Tm3+ doped Na5Lu9F32 single crystal has larger stimulated emission cross-section compared with other crystals. All these spectral properties suggest that this kind of Tm3+doped Na5Lu9F32 crystal with high physical-chemical stability and high-efficiency emission at 1.8 μm may be used as potential laser materials for optical devices.