Optical properties of Er3+-Yb3+ codoped CdF2 single crystals

Er3+ (1%), Yb3+ (4%): CdF2 single crystals with good optical quality are grown by the standard Bridgman method. Absorption, excitation, fluorescence and upconversion spectra are carried out at room temperature. The standard Judd-Ofelt (JO) model is applied to absorption intensities of Er3+ to obtain the three phenomenological intensity parameters by the least square fit procedure. The values obtained are in accordance with those of other fluoride hosts with good root mean square fitting. These JO intensity parameters are then applied to determine the radiative transition probabilities (AJJ′), radiative lifetimes (τrad) and branching ratios (βJJ′) of Er3+ transitions. Green excitation spectrum shows that the Er3+ ions doped CdF2 is preferably excited by 4I15/2 → 4G11/2 (375 nm). The obtained Stokes fluorescence spectrum is characterized by an intense green emission and weak red emission for which we have measured the fluorescence lifetime, the cross-section emission, the gain and the radiative quantum efficiency. Under 980 nm laser excitation, intense red and green upconversion emissions induced by efficient energy transfer between Yb3+ and Er3+ ions were achieved in the investigated matrix via a proposed upconversion process. The spectroscopic data indicate that the studied host may offer visible and infrared laser emission.