Advanced light management by luminescent materials in greenhouse coatings
Being able to have full control over the solar spectrum that enters a greenhouse is the holy grail in
horticulture to increase production per surface area. This is highly relevant as world population is
expected to reach 10 billion in 2050 which means >50% more food production is needed on less
available land. Today removable and permanent anti-reflection coatings (AR) in greenhouses that
increases solar transmission of sunlight and coatings based on reflective shading agents that diffuse light
or reduce light intensity in summertime, are state-of-the-art commercial light management technologies.
There is however a long-standing desire to implement new type of coatings that can convert ultra-violet
(UV) light, not useful to plants, into visible light or photosynthetic active radiation (PAR), in order to increase production-yield up to 7,5%. Recent combined efforts by TUD and Physee has led to a patented
solution to this problem: a luminescent material integrated into the anti-PAR-reflection coating that
absorbs the UV part of the solar spectrum and re-emits the energy as PAR. Our approach will be to use
an industry compatible magnetron sputtering process to deposit Eu2+ doped silicon aluminium oxynitride
(SiAlON) multi-layer coatings with tuneable index of refraction, by alternating the oxygen to nitrogen
content of the reactive sputter gas. The applicants have proven such SiAlON single-layer coatings doped
with Eu, Sm and Tm for electricity generating windows. The first PhD student will take on this challenge
by (i) developing optical simulations of AR-multilayers that include absorbing luminescent layers and (ii)
deposit luminescent multi-layers with increasing level of complexity on structured float glass plates that
provide the diffusion of luminescence light and PAR light that enters the greenhouse.
The second PhD will take on the challenge to realise UV→PAR conversion with removable coatings based
on luminescent phosphors (inorganic micro- or nano-crystalline particles), that can be applied in the
same way as current shading agents. The challenge for this PhD is to (i) develop phosphors that strongly
absorb ultra-violet light and emit with near 100% efficiency PAR light, (ii) find and experimentally verify
the relation between particle size distribution and density on one hand and light scattering properties on
the other hand and (iii) develop an experimental facility to provide a realistic quantification of UV→PAR
conversion and PAR light enhancement %.
The consortium has complementary knowledge and skills enabling a well thought-through valorisation
plan. While TUD has all the needed fundamental knowledge and facilities on luminescent materials, the
WUR is the expert on the relation between light and plant growth. Physee will be the driving force to
apply new technologies together with the Bom Group, a well-known SME regularly implementing
innovative greenhouse technologies. Integration of new luminescent shading agents will be done in codevelopment with DSM coating resins, that has extensive experience with coatings. Sputtered coatings
can be scaled up by Physee in collaboration with a major greenhouse glass supplier.
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