Introduction to Spectroscopy of Cr4+:YAG Transparent Ceramics

This paper focuses on the spectroscopic properties of Cr4+:YAG transparent ceramic. Absorption, excitation, and emission spectra were measured over a temperature range from 5K to 300K. Low-temperature absorption spectra reveal sharp and narrow lines corresponding to partially allowed transitions from the ground state to the crystal field splitting components of the 4T2 energy level. The shape of the excitation spectra was found to be independent of the monitored emission wavelength, indicating that Cr4+ emission originates from the lowest excited state. Low temperature emission spectra exhibit a sharp and narrow ZPL, accompanied by the vibronic sidebands extending up to ~2000 cm-1. Both absorption and emission spectra of the lowest excited state at low temperature consist of a doublet, with a splitting of 28 cm-1. The temperature dependence of the spectroscopic parameters of this doublet is reported. Based on the obtained results, possible explanations of its origin are proposed.