Optical spectroscopy and local structure of Er3+ luminescence centres in СaO–Ga2O3–GeO2 glasses

Optical absorption, luminescence excitation and emission spectra of Er3+ centres in Ca3Ga2Ge3O12:Er glass with Er content of 1.46 wt% are presented and analysed. Luminescence kinetics for the main Er3+ transitions was satisfactorily described by single exponential decays with characteristic lifetimes. Oscillator strengths, phenomenological Judd–Ofelt intensity parameters, radiative decay rates (emission probabilities of transitions), branching ratios and radiative lifetimes for Er3+ centres in Ca3Ga2Ge3O12:Er glass are calculated and compared with the corresponding parameters of the Ca3Sc2Ge3O12:Er3+ garnet and other crystals and glasses. Quantum efficiency, η, of the 4I13/2 → 4I15/2 Er3+ transition is determined. Incorporation peculiarities and local structure of Er3+ luminescence centres in Ca3Ga2Ge3O12:Er3+ glass are discussed in comparison with garnet crystals and oxide glasses. On the basis of the presented results and referenced EXAFS data for Er, Eu and Ho impurities (L3-edge) it has been shown that Er3+ centres in Ca3Ga2Ge3O12 glass occupy network sites with the coordination number to oxygen of N = 6.