Phosphor geometry regulations with separated red and green quantum dot layers for high performance warm white light-emitting diodes

Abstract High performance white light emitting diodes (WLEDs) were fabricated based on green CuInS 2 /ZnS quantum dots (QDs) combined with red CuInS 2 /ZnS or CdSe/ZnS QDs. It was found that the phosphors with a narrow red emission is beneficial for achieving WLEDs with higher luminous efficiency (LE), warmer correlated color temperature (CCT) and better color rendering index (CRI), avoiding the loss of light power in red region. A stacking order configuration for WLEDs was constructed by depositing green QD layers on red ones (CdSe/CIS). The optimized CdSe/CIS QD based WLED yielded an LE of 90.64 lm/W, CCT of 3213 K, and CRI of 80.3, showing an increase of nearly 11% in power conversion efficiency, compared to one with mixed QD layers. The time-resolved PL spectra confirmed the variation in decay lifetimes of phosphor layers with different configurations. The improvement in efficiency was ascribed to less reabsorption loss of red emission when the red light passed through the green QD layer or the reduced energy transfer from green QDs to red ones that occurred in the mixed QD film. The experimental results indicated that improved performances of WLEDs from cold to warm light could be realized by use of structure regulations.