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

Abstract

In this work Y₃Ga₅O₁₂ doped with 8.7 mol% Cr³⁺ (YGG:Cr) far-red phosphor pellets calcined at 1000, 1200, 1300, and 1400 °C temperatures were synthesized by a simple and low cost sol–gel method. The YGG:Cr pellets were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the luminescent properties were studied by measuring diffuse reflection, photoluminescence (PL), PL excitation (PLE) and internal quantum efficiency (QE). The XRD and SEM results have shown that the material becomes more crystalline, uniform and less porous for higher calcination temperatures. XRD results have also shown that the material becomes strained due to the doping with Cr³⁺ ions for the calcination temperature of 1400 °C. The diffuse reflection and PLE spectra have shown three absorption and excitation bands in the UV, blue and red spectral regions. PL was characterized by a broad band in the far-red spectral region that peaked at about 711 nm. QE has shown a strong dependence on the calcination temperature. Furthermore, using the previously synthesized YGG:Cr phosphor powder and a commercial blue InGaN LED, a far-red–blue phosphor converted LED (pcLED) lamp was designed and characterized. Blue–far-red pcLEDs could be used in greenhouses in order to meet the photophysiological needs of plants.