Lifetime prediction of encapsulated CdSexS1-x quantum platelets for color conversion in high luminance LED microdisplays.

Abstract

The LED technology is seen today as the most promising approach to manufacture high luminance color microdisplays for augmented reality application. So far, it mostly involves blue micro-LED technology and quantum dots-based layers for green and red color generation by light down-conversion. Despite significant progress, the viability of this technology still raises many questions. Among them, the stability of the color conversion layer under nominal display operating conditions is still an issue which has not been thoroughly addressed yet. This paper provides experimental data on the aging behavior of CdSexS1-x quantum platelets (QP) for blue-to-red conversion, under a wide range of blue irradiation power. A modeling of the photoluminescence (PL) decrease versus aging time is proposed, that enables to reliably predict the lifetime of a color LED microdisplay in real operating conditions. At room temperature, the alumina encapsulated CdSexS1-x QPs exhibit a lifetime (t70) of 35,000 h under operating conditions representative of a microdisplay emitting 100,000 nits white light, in video mode. With an average daily use of 3 hours, it would represent for a microdisplay more than 30 years. In addition, the study highlights that display heating induces a lifetime decrease related to a thermally activated enhancement of the annihilation rate of PL emission centers. As a result, a display operated at 100,000 nits and 45°C would see its lifetime t70 reduced by a factor 4 (∼8 years), which remains acceptable for most micro-display applications.