Red-Emitting Coatings for Multifunctional UV/Red Emitting LEDs Applied in Plant Circadian Rhythm Control

Abstract

Multifunctional light-emitting diodes (LEDs) formed by coating deep-UV-emitting (<300 nm) LED chips with downshifting phosphors are of great interest for applications in indoor farms as both antibacterial (UV radiation) and photosynthetic agent (red light). Challenges include the fabrication of high-brightness downshifting converter films with controlled thickness excited in the deep-UV spectral region. We address it by optimizing the amount of Ba2SiO4:Eu(III) red-emitting phosphor dispersed in poly (methyl)methacrylate (PMMA), yielding luminescent films with tunable thickness. Taking advantage of the intra-4f6 transitions, the Eu(III) luminescence is used as local probe, pointing out the presence of 8 non-equivalent local sites for the lanthanides. PMMA enables the processing of flexible films and simultaneously acts as a selective filter to deep-UV radiation, controlling the amount of UV radiation for indoor farm applications. Moreover, after the dispersion in PMMA, the Eu(III)-based luminescence remains analogous to that of the isolated phosphor with an absolute emission quantum yield of 0.11 ± 0.01, confirming that Ba2SiO4:Eu(III)/PMMA films display desirable features to be used as coatings of deep-UV emitting LEDs toward multifunctional devices for indoor farm application.

Towards opto-structural parameters to enhance the circularly polarized luminescence brightness of EuIII β-diketone complexes with chiral auxiliary ligands

“…S39, ESI†) of the analogous Eu III and Gd III complexes (for further details, see Note S9, ESI†). 48–50…”

“…S39, ESI †) of the analogous Eu III and Gd III complexes (for further details, see Note S9, ESI †). [48][49][50] To study the kinetics behind the luminescence of the complexes, time-dependent luminescence spectroscopy (Fig. S40, ESI †) was undertaken to assess the 5 D 0 emitting level lifetimes (t = (A rad + A nrad ) À1 ), as presented in Table 1.…”

Unrevealing the opto-structural features of luminescent polymeric films containing EuIII-doped phosphors through spectroscopic and theoretical perspectives

“…61 These interactions keep the phosphor/PMMA particle stable through the weak non-covalent interactions, whose nature will be elucidated subsequently, upon the non-ionic character of the surface of the particles. At high phosphor concentrations, the formation of agglomerates should take place, 62,63 increasing the number of interactions, since the polymer interacts from different positions with the phosphor supercell. 64 Under these circumstances, a high dependency of the CB and VB energies on the phosphor concentration is noted.…”

“…64 Under these circumstances, a high dependency of the CB and VB energies on the phosphor concentration is noted. 62 Furthermore, higher phosphor concentrations in the composite increase the number of structural defects and therefore, the quantity of defect-related electronic levels that lie within the gap 30,65 also contributes to the fluctuations in the band gap energy between the films. However, at this stage, it is not possible to predict the weighted contribution of each mechanism.…”

PMMA or PVDF films blended with β-diketonate tetrakis EuIII or TbIII complexes used as downshifting coatings of near-UV LEDs

“…It is worth pointing out that opaque films can indeed be used as downshifting coatings of near-UV LEDs, but reproducibility and light scattering may be an issue. To increase the amount of complex dispersed in the films, other strategies could be applied, for instance, (i) the use of different deposition method e.g., spin coating, keeping in mind that the deposition parameters must be adjusted to avoid thicker boarders and inhomogeneous luminescence; 38 or (ii) increase the amount of the complex in the polymer (up to 60 wt%) to avoid the formation of particle agglomerates, as discussed in our prior paper, 39 although increasing the amount of the complex does not necessarily improve the luminescence, as larger amounts affect the mechanical features, that is, the films become more brittle, and cause luminescence quenching by concentration. Therefore, the investigation reported here demonstrates how the luminescent and mechanical properties of Ln III complexes can be controlled by choosing suitable amorphous or semicrystalline polymeric matrices and help to map strategies to boost their features for applications as downshifting coatings of near-UV-emitting LEDs suitable for solid-state lighting.…”