The article reports the synthesis and characterization of organic-inorganic hybrid glasses composed of atomically precise nanoclusters. Specifically, [Cu4I4(PR3)2] cubane nanoclusters coordinated by phosphine ligands form robust melt-quenched glasses with reversible crystal-liquid-glass transitions. The protective phosphine ligands significantly influence the glass formation mechanism and modulate the physical properties of the glasses. Among these, [Cu4I4(PPh3Et)2] exhibits superior optical properties, including >90% transmission in the visible and near-infrared wavelengths, negligible self-absorption, a near-unity quantum yield, and high light yield. Experimental and theoretical analyses confirm the structural integrity of the [Cu4I4(PPh3Et)2] nanocluster in the glass state, attributing its enhanced luminescence properties to strong internanocluster CH-π interactions and reduced structural vibration. Additionally, the glass shows promising X-ray scintillation performance, making it a potential candidate for advanced photonics applications. The discovery of "nanocluster glass" opens new avenues for understanding glass formation mechanisms and designing novel luminescent glasses with well-defined building blocks.The article reports the synthesis and characterization of organic-inorganic hybrid glasses composed of atomically precise nanoclusters. Specifically, [Cu4I4(PR3)2] cubane nanoclusters coordinated by phosphine ligands form robust melt-quenched glasses with reversible crystal-liquid-glass transitions. The protective phosphine ligands significantly influence the glass formation mechanism and modulate the physical properties of the glasses. Among these, [Cu4I4(PPh3Et)2] exhibits superior optical properties, including >90% transmission in the visible and near-infrared wavelengths, negligible self-absorption, a near-unity quantum yield, and high light yield. Experimental and theoretical analyses confirm the structural integrity of the [Cu4I4(PPh3Et)2] nanocluster in the glass state, attributing its enhanced luminescence properties to strong internanocluster CH-π interactions and reduced structural vibration. Additionally, the glass shows promising X-ray scintillation performance, making it a potential candidate for advanced photonics applications. The discovery of "nanocluster glass" opens new avenues for understanding glass formation mechanisms and designing novel luminescent glasses with well-defined building blocks.