Light-emitting diodes based on Eu3+, Eu2+ or Tb3+-doped silicates for lighting and Circadian rhythm regulation

White-light-emitting diodes (WLEDs) are the main light sources for indoor and outdoor lightings as well as for backlighting of displays due to their high brightness (800 lm) and luminous efficacy (150 lm·W-1), long lifespan (50,000 hours), low power consumption (8.5 W), low cost (60 dollars over 20 years of use) and environmentally friendly properties compared to the traditional incandescent and fluorescent bulbs. Beyond WLEDs, attention has currently been paid to monochromatic LEDs due to the common consensus on the light impact on human and plant circadian rhythm regulation. Nonetheless, the main challenges are to come up with WLEDs featuring desirable correlated color temperature (4,500 K) and color rendering index (> 90) and work around the “green gap” drawback in the fabrication of green-emitting LEDs. Therefore, the goal of this Ph.D. thesis is to report on the fabrication of white or monochromatic-emitting LEDs, and for this propose, UV-to-green (Ba2SiO4:Eu2+ e Ba2SiO4:Tb3+), yellow (Sr2SiO4:Eu2+) and red (Ba2SiO4:Eu3+) downshifting converter phosphors were synthesized by the sol-gel route, fully characterized and dispersed as polymeric films (PVDF or PMMA), to which were used to coat commercial UV LEDs. The synthesis conditions of the phosphors were changed aiming to optimize phase composition and emission intensity of the dopants. PMMA plays the role of enhancing the luminescent activator emission, and both Ba2SiO4:Eu3+ and Ba2SiO4:Tb3+ phosphors feature the required characteristics to be used as coatings of UV LEDs (250 nm), making multifunctional prototypes emitting UV and red light for simultaneous application in indoor farms by regulating the plant circadian rhythm and as a disinfection agent. On the other hand, the green-emitting LEDs built by coating UV LEDs (365 nm) with Ba2SiO4:Eu2+/PMMA films match high luminous efficacy and radiant stability, among the best values reported so far, being a practicable alternative to supply the absence of commercially-available high-efficient green-emitting LEDs. Finally, WLED prototypes built by combining UV LEDs (395 nm) and Sr2SiO4:Eu2+/BAM:Eu2+/PMMA films display luminous efficacy and radiant stability among the best reported, and correlated color temperature depending on the phosphor mixture proportion, that may be tuned for daylight (6,000 K) and night light (3,500 K) applications, as well as phototherapy and backlighting of displays. (AU)