Crystal growth and spectroscopic properties of Cr3+-doped CaGdAlO4

A Cr3+:CaGdAlO4 single crystal with dimensions of ∅21 × 33 mm3 was grown successfully by Czochralski method for the first time. Its spectral properties including polarized absorption spectra, polarized fluorescence spectra, excitation spectrum and fluorescence decay curves were investigated in detail. The absorption cross-sections at around 573 nm corresponding to the 4A2 → 4T2 transition of Cr3+ ions are 4.75 × 10−20 and 2.56 × 10−20 cm2 for σ- and π-polarizations, respectively. The excitation spectrum shows two broad and intense absorption bands at about 390 nm and 570 nm, which are associated with the 4A2 → 4T1 and 4A2 → 4T2 transitions of Cr3+ ions, respectively. The emission band with peak at around 744 nm is ascribed to the 2E → 4A2 transition of Cr3+ ions, with the emission cross-sections of 5.55 × 10−22 and 5.41 × 10−22 cm2 for σ- and π-polarizations, respectively. The fluorescence lifetime is 4.35 ms at room temperature. The Dq/B value is 2.72, which means that Cr3+ ions occupy the lattice sites with strong crystal field strength. The results show that Cr3+:CaGdAlO4 crystal can be regarded as a potential laser gain medium.