Enhanced and modulated visible luminescence of Pr3+:CaF2 crystal by co-doping R3+ (R=Y, Gd, Lu) ions

Highlights: • A series of 0.6 at% Pr:CaF₂-RF₃ (R= Y³⁺, Gd³⁺, Lu³⁺) crystals were successfully grown by the temperature gradient technique(TGT) method. • By co-doping R³⁺ ion (R=Y³⁺, Gd³⁺, Lu³⁺), the spectral performance of the crystals could be significantly improved and the function effect is also different. • The spectral performance and spectral quality factor of the crystals were systematically described and compared for the first time. • The spectral modulation effect caused by Y³⁺, Gd³⁺ and Lu³⁺ co-doping ion was discussed. -- Abstract: A series of 0.6 at% Pr:CaF₂-RF₃ (R = Y³⁺, Gd³⁺, Lu³⁺) crystals have been successfully grown by the temperature gradient technique(TGT). The absorption spectra, fluorescence spectra, and fluorescence decay curves were measured and analyzed at room temperature. When the R³⁺ concentration is higher than a certain value, the diffraction peaks of Pr:CaF₂-RF₃ crystals were well indexed to the (Ca,Y)F₂ phase. By co-doping R³⁺ ion (R=Y³⁺, Gd³⁺, Lu³⁺), the spectral performance of the crystals could be significantly improved and the function effect is also different. For 0.6 at% Pr, 28.5 at% Y:CaF₂ crystal, the fluorescence lifetime of ³P₀ energy level was fitted to be 45.46 µs, and the emission cross sections of ³P₀→³H₆ (605 nm), and ³P₀→³F₂ (641 nm) were calculated to be 1.78 × 10⁻²⁰ cm², and 4.61 × 10⁻²⁰ cm² with the full width at half (FWHM) of 20.1 nm and 6.8 nm, respectively. The 0.6 at% Pr, 28.5 at% Y:CaF₂ crystal could be favorble laser medium for ultra-fast laser opreration at 605 nm and 641 nm. For 0.6 at% Pr, 18 at% Gd:CaF₂ and 0.6 at% Pr, 10 at% Lu:CaF₂ crystals, the spectral quality factors σ_em• τ_f of ³P₀→³F₂ transition (642 nm) were calculated to be 614.18 × 10⁻²⁰ cm²• µs and 506.36 × 10⁻²⁰ cm²• µs with the FWHM of 3.7 nm and 5.3 nm. All the results show that 0.6 at% Pr, 18 at% Gd:CaF₂ and 0.6 at% Pr, 10 at% Lu:CaF₂ crystals are promising gain media for high-efficiency visible laser output at 642 nm, which would compete with commercial Pr: YLF crystal in the future.