overall studies, we first start with a general overview

overall device
efficiency. Despite
this challenge, significant improvements have been realized within the past decade.
Another difficulty arises
from the issues
related to charge
accumulation and photocharging effects for operation over a long time.
For further information on this topic,
we recommend the excellent reviews written by Rogach et al.

11 and
Wood and Bulovi? 12.
Here, we focus
on the QD- WLEDs based on color
conversion using
QD photolumines- cence rather than QD electroluminescence. Since
there is no carrier injection into QDs in these devices,
they do not suffer from the problems
of the electrically excited ones. Although there is some energy loss
due to the conversion of highly energetic photons (usually blue or UV) to low energy photons
to generate white light (Stokes’ shift),
the energy penalty is not as severe as the efficiency reduction due to charge injection in the case of electrically excited QD-based LEDs. It is also worth mentioning here that, although realizing color
conversion using
this method can be simple, generating high quality white light suitable
for general lighting applications requires very careful
colori- metric and photometric optimizations which depend on a deeper understanding of the color
science and photometry. In order to obtain the desired performance, scientists and researchers all around the world have carried out studies, both experimentally and theoretically, resulting in
significant improvements in the area. In this review, we summarize these developments on general lighting
and display
backlighting where QDs replace the conventional color-converting
phosphors.
Before covering the reported studies, we first
start with a general overview of color science and photometry, which basically introduces the figure-of-merits
for general lighting applications. Subse- quently, wereview the research
on the spectral design
of QD- integrated white LEDs (QD-WLEDs) for indoor and outdoor lighting applications. Then we continue with a summary
of the experimental demonstrations of QD-WLEDs.
The sub- sequent section is devoted to the application of QDs as LCD backlights. Finally,
we conclude the review by discussing

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the future outlook
and challenges for QDs and their
LEDs.

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