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In neodymium-doped fluorozirconate-based glasses, a huge increase of up to a factor of 20 of the Nd3+photoemission is possible by the introduction of BaCl2nanocrystals. A rate equation system was developed to describe the excitation and relaxation dynamics of neodymium ions in such composite matrix to quantify the enhancement mechanism due to the embedded nanocrystals. The model is extended to include the previously unknown quantitative nanocrystal influences in an effective-medium model, considering the change in the phonon spectrum in particular. Having verified the coefficients with time-dependent photoluminescence experiments, it is used to predict the intensity dependence of steady-state upconversion. The good agreement with experimental data indicates that the rate equations enable the quantitative simulation of photon upconversion in glass and glass ceramics under a variety of excitation scenarios. In addition, the strong reduction of the phonon emission probability in the BaCl2nanocrystals is confirmed as the key reason for (upconversion) emission enhancement in the fluorozirconate-based glass ceramics.

The optical properties of Nd3+ions embedded in fluorochlorozirconate glasses were studied, addressing in particular the effect of BaCl2nanocrystal growth in the matrix upon annealing. A Judd–Ofelt analysis for these glasses and for a Nd3+-doped fluorozirconate reference glass without nanocrystals yielded various radiative decay rates as a function of nanocrystal size. For the 4F3/2to 4I9/2transition, where multiphonon relaxation is negligible, the rates agree very well with experimental results. Further support for the validity of the Judd–Ofelt results was obtained using an alternative approach for the determination of radiative decay rates involving emission and absorption spectra and their connection through the McCumber theory and the Füchtbauer–Ladenburg equation. The obtained variations of the Judd–Ofelt intensity parameters Ωλreflect systematic changes in the local environment of the Nd3+ions as an effect of the BaCl2nanocrystal growth, indicating partial inclusion of Nd3+into the nanocrystals.