Recently, LTA-Se(1–8) samples with 1–8 Se atoms per cavity (simplified unit cell, large cavity + sodalite cage) obtained via adsorption at the temperature of ∼450 °C were reported. It was shown that single Se8 or single Se12 ring are formed in the large LTA cavities, Se8/Se12 ring concentration ratio decreasing with an increase in the Se loading density. Contrary, in the present work, using Se vapour adsorption at ∼550 °C, we succeeded in encapsulation of ∼17 Se atoms per cavity (LTA-Se(17)) with a significant increase in the Se8/Se12 concentration ratio manifesting double Se8-ring cluster formation in the most of the LTA large cavities, which is a step towards cluster crystal fabrication. According to our polarization/orientation Raman spectroscopic study of LTA-Se(17) single crystals, the orientations of the Se8 and Se12 appeared to be similar to those in previously investigated LTA-Se(1–8). Importantly, luminescent Se2− anions, oriented along the LTA 4-fold axes and located in the sodalite cages, are detected via Raman polarization/orientation dependencies of LTA-Se(17). Bright Se2− light emission with a maximum at ∼1.56 eV and vibronic structure is observed in the 1.3–1.8 eV spectral range. We show that the anions experience a compression in LTA which is slightly relaxing with a decrease in temperature producing an anomalous Raman band downshift. The compression of Se2− in LTA is weaker/stronger than that in sodalite/cancrinite, luminescence band photon energy depending on its strength. High concentration of regularly arranged Se2− in LTA suggests considering LTA-Se(17) as an important novel light-emitting material.