Effects of Gd3+/Y3+ codoping on the spectral properties of Nd:CaF2 crystals

In the last few years, Nd3+ doped fluoride crystals have achieved some amazing laser performances by codoping buffer ions such as Y3+ and Gd3+ ions, which lead to the changing of local structure of Nd3+ ions. In this work, effects of doping concentration of Gd3+ and Y3+ ions on optical properties are discussed. The relationships between spectroscopic properties and the unit cells are also discussed. Nd, Y:CaF2 and Nd, Gd:CaF2 disordered crystals are grown by using temperature gradient technique (TGT). Among 0.5 at.%Nd, x at.%Gd(x=2, 5, 8, 10):CaF2 crystals, the crystal with Gd3+ of 2 at.% has the longest fluorescence lifetime (499 s). Increasing the concentration of Gd3+ up to 5 at.%, the crystal has a maximum absorption cross section of 1.910-20 cm2, and a maximum emission cross section of 1.910-20cm2. The crystal with Gd3+ of 8 at.%has a maximum emission bandwidth of 29.03 nm(FWHM). Among 0.6 at.%Nd, x at.%Y(x=2, 5, 8, 10):CaF2 crystal, the crystal with Y3+ of 5 at.%has the biggest absorption cross section (2.4110-20 cm2), and the biggest emission cross section (3.1710-20 cm2), when the concentration of Y3+ is 5 at.%. When the Y3+ concentration increases up to 10 at.%, the crystal has a longest fluorescence lifetime of 359.4 s and maximal emission bandwidth of 26 nm(FWHM).The different concentrations of codoping ions have different effects on the Nd:CaF2 crystals, for the formations of different optical centers. In order to study the effects of local structure around Nd3+ on the optical properties in a set of Nd:CaF2 single crystals with different codoping concentrations of Gd3+ and Y3+, the unit cell parameters are investigated by X-ray diffraction. With different concentrations of Gd3+ and Y3+ ions in Nd:CaF2 crystal, the local structure of Nd3+ changes, which leads to different optical properties. The relevant details will further be explained in this paper.