Sol-gel synthesized far-red chromium-doped garnet phosphors for phosphor-conversion light-emitting diodes that meet the photomorphogenetic needs of plants

Abstract

We report the sol-gel synthesis and characterization of far-red garnet phosphors Gd(3)Ga(5)O(12) (GGG:Cr), Y(3)Ga(5)O(12) (YGG:Cr), Lu(3)Ga(5)O(12) (LGG:Cr), and Gd(3)Sc(2)Ga(3)O(12) (GSGG:Cr) doped with different chromium (III) concentration (3, 5, and 8 mol. %). The morphological and luminescence properties of the phosphors annealed at different temperatures (1000°C, 1300°C, 1400°C, and 1500°C) were examined using x-ray diffraction, scanning electron microscopy, photoluminescence (PL), and PL excitation (PLE) spectroscopy, and by the measurements of diffuse reflection, PL internal quantum efficiency (QE), and PL decay time. The PLE spectra of the samples were found to peak at around 450 nm depending on the host, and luminescence was observed in the region of 700-760 nm. The QE was found to strongly depend on doping concentration and calcination temperature, and the PL decay exhibited biexponential behavior. The investigated far-red garnet phosphors, in particular GGG:Cr and YGG:Cr, show a potential for use in phosphor-converted light-emitting diodes that meet the photomorphogenetic needs of plants.

Cr3+ doped yttrium gallium garnet for phosphor-conversion light emitting diodes

“…It is seen that the values of QE increase for higher calcination temperature until it reaches 55% for 1300 °C calcination temperature and saturates. This value is even by 9% larger than the QE of the YGG:Cr 3+ 8 mol% phosphor powder [17]. The growth of QE can be explained by the improvement of crystal properties of the crystallites that form the pellets, as it is seen in Fig.…”

“…Since phosphor pellets still cause technological difficulties while designing a light converter, a pcLED based blue-far-red lamp was designed using the farred YGG phosphor powder doped with 8 mol% Cr 3+ and calcined at a 1300 °C temperature that was synthesized by a sol-gel method at the Department of Inorganic Chemistry, Vilnius University [17].…”

“…This can be confirmed by the diffuse reflection spectra that show the absorption in the far-red region where PL takes place being higher for the pellet calcined at 1400 °C if compared to other samples. and intensity variation to the spectra of the YGG:Cr phosphor powder investigated before [17]. Fig.…”

“…However, in none of this research the values of internal quantum efficiency (QE) are presented which is a very important property of phosphors for LED applications. For this reason, using a simple and low-cost sol-gel method we have previously synthesized and investigated various powder (gadolinium, gadolinium scandium, yttrium and lutetium) gallium garnets calcined at different temperatures and doped with different Cr 3+ concentrations [17]. The results have shown that the most promising material was yttrium gallium garnet Y 3 Ga 5 O 12 :Cr 3+ (YGG:Cr) 8 mol% calcined at 1300 °C temperature.…”

“…Furthermore, using the YGG:Cr phosphor powder described in Ref. [17] and a blue InGaN LED, a blue-far-red solid state lamp for greenhouse lighting was designed and its spectral properties such as photon flux and the efficiency of blue-to-far-red light conversion were measured. , Ga 3+ and Cr 3+ with a desired molar ratio were mixed together and the necessary amount of TRIS was added.…”