Flexible micro-scale UV-curable phosphor layers screen-printed on a polymer substrate for planar white light-emitting diodes

Different types of the remote phosphor have been investigated to enhance the light-emitting performance with less time-dependent degradations of the emission properties. Here, two different remote phosphor approaches are introduced to optimize the effect of red phosphor in the yellow phosphor-driven white light-emitting diodes (LED)s. These approaches combining the printing technology with a UV-curing process are designed for flexible planar white LEDs with a thin layer thickness of a few tens of micrometer-scale. A screen-printing process was utilized to obtain the mixed or stacked phosphor layers based on commercial yellow and red phosphors. The phosphor particles were found to be dispersed uniformly in the cured UV-polymer matrix. The resultant luminescence characteristics depended on the type of remote phosphor and the relative content of red phosphor. The mixing approach was more effective in raising color rendering index (CRI) while minimizing the reduction of luminous efficacy. As a result, a luminous efficacy of ∼101 lm/W and a CRI of ∼83.1 were obtained for the mixed sample with 5 wt% red phosphor, which correspond to a decrease of ∼11.2% and an increase of ∼9.3% compared to the reference sample.