# Unexpected Performance of a Bifunctional Sensitizer/Activator Component for Photon Energy Management via Upconversion

## TL;DR

A new material combination efficiently converts low-energy yellow light to high-energy blue light at room temperature, offering potential for improving solar energy technologies.

## Contribution

A bifunctional sensitizer/activator enables efficient upconversion without triplet energy transfer, surpassing existing methods by orders of magnitude.

## Key findings

- Yellow-to-blue upconverted photoluminescence is achieved at room temperature with ultralow power.
- The UC-PL quantum yield is 2.5%, exceeding traditional TTA-UC materials by over three orders of magnitude.
- Bimolecular annihilation reactions between triplet-excited molecules facilitate the upconversion process.

## Abstract

We here report on the observation of upconverted photoluminescence
(UC-PL) from the blue-light-emitting 9,10-diphenylanthracene (DPA)
mixed with the yellow-light-absorbing bifunctional sensitizer/activator
component of (3,3,7,8,12,13,17,18-octaethylporphyrin-22,24-diid-2-one)
PtII (PtOEP-K). Yellow-to-blue UC-PL (0.680 eV spectral
upshift) is achieved at room temperature under ultralow power continuous
incoherent photoexcitation (220 μW/cm2) despite the
absence of triplet energy transfer (TET) between PtOEP-K and DPA.
Under selective CW-laser photoexcitation of PtOEP-K in DPA:PtOEP-K,
a 2.5% UC-PL quantum yield is obtained; that is an improvement exceeding
by more than 3 orders of magnitude the UC-PL quantum yield of TTA-UC
material combinations wherein no TET is operative. The PL response
of DPA:PtOEP-K to varying laser fluence suggests that bimolecular
annihilation reactions between triplet-excited PtOEP-K facilitate
the UC-PL activation in DPA. These findings pave the way toward low-complexity
strategies for the reduction of transmission losses in solar energy
technologies through an innovative wavelength upshifting protocol
involving excitonic materials.