Mo m present_monday_light interacting materials

www.mattersofmatter.eu Light Interacting Materials
Light Interacting Materials
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Phosphorescence

Writing with light on photoluminescent materials
• Do all colours activate photoluminescence ?
• Does it depend on their intensity?
• How’s the emitted light color compared to
the excitation light?
Light should be of the right frequency
• No matter the intensity /power
• Higher f than the emitted one
• The material should be able to absorb f
 Quanta of light
the energy appears
to be concentrated
in discrete packets
called photons.
Photoluminescence
can’t be explained
by light wave theory
YOU NEED
• LED Torch, UV Torch
• Colored filters (blue, red, …)
• Photoluminescent paper
• Red lamp 100 W

Photoluminescence …how does it work?
1. All electron transitions from the
excited to the ground state are
non-radiative except for the last
one.
2. Energy conservation
part of E is lost as heat due to
vibrations --> the emitted light is
of lower frequency/longer
wavelenght = less energetic
3. If the vibration is less intense
(i.e. liquid nitrogen) -> change in
the emitted colour (higher f) may
be observed.*
4. Excitation energy may be also
chemical (chemiluminescence) , or
mechanical (triboluminescence)
1
2
4
3 See video how florescence works slide 9

Studying emissions of photoluminescent samples
WHEN SHOULD YOU TURN ON THE UV LEDS ?
EVERY 0,02 SEC FOR 0,001 SEC
Rare Earths/Inorganic Aluminates: «poor, dim» eco light
from atoms (visible in almost total darkness)
• not radioactive,
• lasting 8 hours: after 1 hour 90% of light decay then
stable for 7 hours approx.
• little % of heavy metals, 20 times less than USA regulations
• everlasting, recyclable,

http:// lucedentro.com
Alienskin
L.E.S.S
RURAL ECO STREET
LIGHTS
Photoluminescence
for energy saving
Applications

Fluorescence - When light excitation ceases
light emission stops almost immediately
(10^-8 sec)…
… while in Phosphorescence light is still
emitted long after excitation is over
Phosphorescence VS FluorescencePhosphorescence VS Fluorescence
By Jacobkhed - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=18456013
Common processes of electron
interaction with light. Absorbed
radiation may be emitted by
vibrational relaxation,
fluorescence, or phosphorescence

Fluorescence
Turn on your Black Light!
= UV light

Detergents, toothpaste
Anti counterfeiting
Bleached paper
Hot glue
Minerals
Tonic water
Testing water for
Petroleum Jelly –
Vaseline
contamination
Body fluids
blood,
urine
semen
Bocteria, moulds
https://www.youtube.com/watch?v=CcssdJf0pKQ

Acrylic fluorescent
sheets/rods

Can you imagine PV solar concentrators?
Drawbacks
• Sun Tracking mechanical movement
• Large reflecting area
• Rather large PV cell area
• Superheating in focus -> efficiency loss
• Difficult (and dangerous!) to integrate
in buildings
OPTICAL CONCENTRATORS:
MIRRORS + LENSES
Source http://atlascuisinesolaire.free.fr public domain

Acrylic fluorescent PV concentrators
• Optical effect or real concentrators?
• Acrylic rods VS fiberoptics
• Refraction plus fluorescence
• Harvesting best in diffused light

1
The Physics behind it: light guide + fluorescence
Reflected
Light guide:
concentrated
at the edges
Transmitted
& Escaped
The incident radiation is «compressed» in the
wavelengths that optimize the PV cell efficiency 
Used in stacks to exploit different kinds of solar cells
Source: By Levita.lev (Own work) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)
or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
Multiple
total internal
reflections

1
Red
1m
Yellow
0,5m
Green
0,25m
Can you explain what’s happening?

1
FACTS
If you shine light from one of the extremities
• Incident light is white, the acylic rod is yellow green fluo
• The longer the rod, the more the emitted light turns to
reddish
Possible (consinstant) explanation
• The longer the rod and the greater the possibility that the
green component light will be absorbed by the
fluorescent pigments which riemit in red (possible more
pigments absorbing UV riemitting green and absorbing
green riemitting Red)
• Is it the same with blue and UV light?
spectrophotometer
• Test PV cells with different rod lengths
Is there an optimal length for best
efficiency?
• Is the effect the same even if you shine
from the
side surface?

Acrylic fluorescent
sheets for
-indoor photovoltaics
-smart windows
-harvesting in diffuse
light (Northern
countries)

1
Seen at International
Makers Faire Rome
October 2015
Inspiration …

1
• Eni photovoltaic shelter can reach a 500 Watt [nominal]
production of Electrical Energy
• 192 yellow clear sheets .
• Pigments have been specifically patented by ENI
• https://energy.closeupengineering.it/en/luminescent-solar-concentrator-lsc/9655/
ENI Photovoltaic Shelter
Eindhoven University of Technology
A2 Den Bosch
The Netherlands
Free download @
https://pure.tue.nl/ws/files/14501512/2016_02_04_SEBC_Ka
nellis_M.pdf

Engineering challenges • What’s the gain of having solar cells at the
edges? What’s the efficiency?
• How much surface is needed to harvest
enough light? Edges loss?
• Best acrylic sheet colour?
• Best incident light colour? Best incidence
angle?
Ratio of Edges surface/Harvesting area
VS PV cell efficiency or output for a fixed
luminance.
Direct or diffused light?
1
1/2
1/8
1/4
N.B BEST example of PBL
and IBSE open inquiry
Alligned with cutting edge
research
makers faire 3^,4^
Maturità 5^

www.mattersofmatter.eu Light Interacting MaterialsThe acrylic fluo PV solar
concentration lamp
Rome Makers Faire
European edition 2016!

PV cells

1
1^ generazione : silicio monocstallino
Alta efficienza>25%
Sole pieno
2^ generazione : film
sottile silicio amorfo
Alta resistenza
(Flessibilità )
Anche luce diffusa ea
bassa intennsità
3^ generazione: organico e ibrido
Polimeriche o organiche
flessibili
Bassi costi di produzione
Possibilità di fine tuning delle proprietà molecolari

Investigate the best option for
• Building facades
• Curved surfaces
• Roofs with possible shadow casting elements
• Indoor applications
• Portable applications
• IoT, wearables and pervasive sensors network
Test
• Illuminance lux (luminous flux per unit area)
• Light intensity, direct/diffuse light, incidence
angle dependance
• Light source, incident wavelenghts, UV, IR
• Efficiency
PV cells: 3° generation and beyond …

1Angle
Wavelength

Dichroic film/glass

Can you guess the missing colour?
?

Reflected and transmitted frequencies are
complementary ones
If the background is not black some of the
transmitted light is reflected back, hence the
colour of the glass (third color)

1
The two most common types of filters in use today are absorption filters that absorb unwanted wavelengths and
interference filters that remove selected wavelengths by internal destructive interference and reflection.
Colour filters
secondary absorption
 Hot filters
more accurate & efficient
 Cool filters
Magenta traditional filter:
absorbs green light
Magenta interference filter:
reflects green light
REFLECTION

YOU NEED
• Black and white paper
• Dichroich glasses
YOU NEED
• Add a mirror
The mirror reflects back all light. Transmitted light
combines with reflected one and makes
white!looks transparent

1
• The colors shown are in reflection
since there is no loss (no absorption),
• the colors in transmission will be
complementary.
• Top row shows subtractive primary
colors (yellow- cyan- magenta) but
those in transmission will be additive
(red green and blue)
• vice versa for the lower three

Black & white paper
+ mirror
The photographer is
shadingn the
bottom right corner
Only black &
white paper.
The
photographer
is shading the
disk bottom

«Chamaleon film»
Transmitted/reflected colours depend on
both viewing angle & light incidence angle
Angle Transmitted 
… … …

1
References

Same effect with dichroich film, a cheaper
aletrnative to dichroic glass
composed of hundreds of layers of polymer
films with different refractive indexes.

1
“Place the radiant light film on a white sheet of paper - tilt it at different angles and
observe the different colors. Now place against black background and tilt – is
there a difference in its appearance?
Fold a piece over, creating two layers. If you sandwich the layers flat against
each other and repeat the experiments does anything change?
Now hold the folded over piece so that there is some space between the layers
(put a finger or two between the layers) and shine light in the middle. Can you
produce green or other colors you couldn’t produce when the material was just
one layer?»
Source: http://sci-toys.com/scitoys/scitoys/light/permanent_rainbows/permanent_rainbows.html
More puzzling questions …

1
The Physics behind it: thin-film interference
Dichroic filters are manufactured using multi-
layered thin film coatings that are deposited on
glass using vacuum deposition. They work on
Interference principle
Through the number and thickness of the
films and the angle of the incident light,
control over the color of light produced is
possible
http://www.sciencecalculators.org/optics/thin-films/
https://upload.wikimedia.org/wikipedia/commons/2/2e/Thin_film_interference_-_oil_film.gif
coating
glass
*
*
*phase change 180° - half
wavelength
ejs_bu_ThinFilm –Java - off line

1
Thick films VS thin films
A. Why thick films DO NOT exhibit visible interference?
R. ATTENUATION (= amplitude decreases)  colours
are too faint to be observable

Thin films: APPLICATIONs
• Laser mirrors
• [Superhydrophobic surfaces]
• Low Emissivity coatings (E-coatings)
reduce heat loss in winter
decrease heat gain in summer
• …
Thursday:
«Climate change &
the 2 °C challenge»

Creativity and
innovation

www.mattersofmatter.eu Light Interacting MaterialsMoM-Light for design…
«Change your light» VIDEO
Smart lamps with new materials

www.mattersofmatter.eu Light Interacting MaterialsMoM-Light for design…

MoM-Light for design…

Polarization

Polarized ballet
Plastic (no stress no
birifrangence) +
Sellotape
Superimposed layers
• How many?
• At what angles?
Put it between PC screen
(open a white page)
and polarization filter
NOW ROTATE the
polarization filter!
AWESOME!

Polarized lamps: 360° of colours
This lamp exploits the light emitted by a bulb and polarised by
two polariser filters. Between the two filters you can put
superimposed layers of plastic, cellophane or tape to create
optical effects with a lot of different colour shades changing
as the filters rotate.

1
A Systematic study

Mo m present_monday_light interacting materials

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