Strategy to probe multimodal light emissions from Eu/Yb activated garnet nanophosphors for LED devices and solar cell applications.

This study investigates multimodal light emission from an Eu/Yb activated YGaO (YGG) nanophosphor synthesized using a low temperature solution combustion method. The prepared sample possesses a cubic phase and an 3̄ space group and this is confirmed with X-ray diffraction and Rietveld refinement analysis. The synthesized sample shows orange-red emission bands because of the f-f transitions of Eu under UV (393 nm) and NIR (980 nm) excitations downshifting (DS) and upconversion (UC) processes, respectively. Upon UV (393 nm) excitation of the sample, the Eu ions absorb this energy and then transfer it to a neighboring pair of Yb ions giving NIR emission (900-1100 nm) corresponding to the F → F transition of Yb. The energy transfer from a single Eu ion to a pair of Yb ions is possible because of the quantum cutting (QC) process and this energy transfer efficiency is found to increase with the increasing concentration of the Yb. The quantitative estimation of energy transfer and internal quantum cutting efficiency is determined by measuring the decay kinetics. An activation energy of 0.25 eV indicates the good thermal stability of the sample. Furthermore, samples are suitable for use in practical applications in lighting devices by combining them with the near-ultraviolet (NUV; InGaN) chip. The fabricated LED device shows stability with the driving current flow values. Studies indicate that the present nanophosphor could be useful for display devices, and in enhancing the spectral conversion efficiency of the solar cells.