Sunlight spectrum down-converting films absorb UV/blue sunlight and convert it in near infrared (NIR) radiation that generates electricity in conventional photovoltaic (PV) cells more efficiently. In this paper we report on down-convertors in the form of polymer nanocomposite films impregnated with nanoparticles of lanthanide phosphor NaYF4:Yb3+, Tm3+ . This compound was synthesized using the wet method and ball-milled in nano-powder. The phosphor produced relatively intense NIR radiation if the region between 960 and 1100 nm with a quantum efficiency of ~5%. It was chemically stable and could be transferred in the polymer film using the open-air concurrent multi-beam multi-target pulsed laser deposition (CMBMT-PLD). Two beams from a Q-switched Nd:YAG laser at a wavelength of 1064 nm were used to ablate two targets. One PLD target was made of compressed nano-powder of the phosphor. The second target was made of polymer poly (methyl methacrylate) known as PMMA. The phosphor preserved its down-converting properties during the deposition and mixing with the polymer. The deposited PMMA+NaYF4:Yb3+, Tm3+ nanocomposite films responded with uniform, mostly blue upconversion radiation to the testing illumination with a NIR laser diode at 980 nm. This proved that the phosphor nanoparticles were evenly distributed in the polymer matrix and preserved the optical properties of the PLD target. Post-deposition heating was shown to significantly improve uniformity of the nanocomposite films.
There is a great interest in photonic substances with permittivity approaching zero, which are called the epsilon-nearzero (ENZ) materials. They have a potential for multiple applications in telecom industry. The newest ENZ materials based on transparent conductive oxides (TCOs) and transparent conductive nitrides (TCNs) still have limited spectral bands of the ENZ effect. We show with simulations based on the Effective Medium Theory that the limitation can be defeated by using nanocomposite films made of several TCOs/TCNs with the ENZ effect observed in different regions of optical spectrum that stand apart from each other. We proposed to make such composites with the concurrent multibeam multi-target pulsed laser deposition (CMBMT-PLD). The composite films of aluminum and gallium doped zinc oxide (AZO-GZO) at different proportions were made by concurrent PLD of AZO and GZO targets with two 532-nm laser beams from a frequency doubled Q-switched Nd:YAG laser in a 10-5-Torr vacuum. The deposition time varied from 10 to 50 min. The high-resolution scanning electron microscopy revealed that the films deposited on glass substrates were composed of nano-grains of the constituents with a size in the range 10-300 nm. Energy dispersive X-ray spectroscopy showed the presence of all the major constituents in the films. Optical absorption and reflection spectroscopy of the films in the visible and near-infrared regions demonstrated that they had a minimum of reflectance corresponding to the ENZ effect in a broad band (~ 200 nm) around 1200 nm in the agreement with theoretical predictions.
We report on the polymer nanocomposite coatings doped with the nanoparticles of rare-earth (RE)-doped fluoride phosphor NaYF4:Yb3+, Er3+ for luminescent solar concentrators (LSCs). Concurrent multi-beam multi-target pulsed laser deposition (CMBMT-PLD) of the phosphor and a polymer conducted in open air was investigated as a candidate process for such coatings. Polymer poly(methyl methacrylate) known as PMMA was considered to be deposited on a glass substrate from a solid target using fundamental harmonic (1064 nm) of a Q-switched Nd:YAG laser concurrently with the phosphor. The sun light was absorbed by the phosphor nanoparticles embedded in polymer film and converted into near-infrared (NIR) radiation via the mechanism of downconversion (quantum cutting). The NIR radiation propagated via the glass substrate as a light guide and was converted into electric power with photovoltaic cells attached to the edges of the glass plate. The polymer did not exhibit degradation during the open-air deposition process. The proposed method is capable to coat economically commercial window-size substrates. The polymer nanocomposite LSCs have broad absorption band covering a significant portion of the solar radiation spectrum, high spectral conversion efficiency, and low reabsorption due to minimal overlap between the absorption and emission spectra (large Stokes shift).
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