Up‐Conversion Fluorescent Labels for Plastic Recycling: A Review

Abstract

The world's plastic production reached 269 million tons p.a. in 2015. The EU fraction of this was 50 million tons, with 40% of this attributed to product packaging. [1] Even though packaging exhibits the highest recycling rate for any plastic product, this recycling rate in the EU is less than 40%. [1,2] Overall, 29.7% of the plastic within the EU was recycled, with the remainder either burnt for energy recovery (39.5%) or dumped in landfills (30.8%). Recently adopted EU legislative proposals on waste management put pressure on the industry to find solutionsThe demand for more efficient and complete sorting techniques for plastic waste is growing, and one possible solution isbased on fluorescent labeling. Novel fluorescent labels based on trivalent lanthanide (Ln 3+ ) activated inorganic up-conversion (UC) materials offer a promising technological solution for plastic recycling. UC is a nonlinear, anti-Stokes process of combining two or more low energy near-infrared (NIR) photons to obtain the emission of a single higher energy photon. While Ln 3+ based UC materials possess one key disadvantage -low quantum yield, they also exhibit many unique features, such as high signal/noise ratio, tailored emission color, long photoluminescent lifetime, and low toxicity. These unique features endear them for a diverse range of applications and offer many new opportunities. Herein, we review the recent advances in the Ln 3+ activated inorganic micro-sized UC materials from the perspective of tailoring UC emission color and intensity for plastic recycling applications.

Understanding and tuning blue-to-near-infrared photon cutting by the Tm3+/Yb3+ couple

“…Consequently, only NaYF 4 is a promising host material to achieve photon cutting for silicon photovoltaics with the Tm 3+ /Yb 3+ couple. We can rationalize our results by considering the maximum phonon energies of the four host materials: 6,27 the more phonons required for phonon-assisted cross-relaxation, the lower the rate 28 . Our work highlights the possibility of tuning the energy-transfer pathways in lanthanide-based phosphors with the appropriate choice of host material and thereby achieving photon-conversion efficiencies above 100%.…”

“…The energy level structures of the lanthanides, however, offer more colourconversion possibilities. Unconventional energy-transfer pathways between lanthanide dopants can be designed, which lead to 'upconversion' luminescence [4][5][6] or 'photon cutting' 7,8 . Upconversion involves merging of the energy of multiple photons by the phosphor material, i.e., it absorbs two (or more) low-energy photons and emits one higherenergy photon.…”

Kunststoffidentifikation und ‐sortierung in der Circular Economy durch Fluoreszenzmarker

“…Während bei Yb‐Er bzw. Yb‐Ho die Up‐Conversion ein Zwei‐Photonen‐Prozess ist, ist sie bei Yb‐Tm ein Drei‐Photonen‐Prozess (aus ).…”

Enhanced upconversion in one-dimensional photonic crystals: a simulation-based assessment within realistic material and fabrication constraints

“…Upconversion (UC) is the process of converting two (or more) photons into one photon of higher energy. It is relevant in a broad range of applications, from anti counterfeiting [1,2], plastic recycling [3], bioimaging [4,5] and theranostics [5][6][7] to photovoltaics [8][9][10][11]. In photovoltaics, UC enables the utilization of sub-bandgap photons, which for silicon-based solar cells raises the theoretical efficiency limit from ≈ 30% [12] to ≈ 40% [8].…”