White light generation from Dy3+-doped yttrium aluminium gallium mixed garnet nano-powders

Yttrium aluminium gallium garnet (here after referred as YAGG), Y3Al5−yGayO12 (where y=1.0, 2.5 and 4.0), nano-powders doped with 1.0 mol% of dysprosium (Dy3+) ions were synthesised by the citrate sol-gel method. The structure, phase evolution, morphology and luminescence properties of these nano-crytalline powders were characterized by means of XRD, FTIR, Raman, electron microscopy and UV-vis spectroscopy. From the XRD results, the crystallite sizes were found to be in the range of 18-26 nm. Excitation spectra of YAGG nano-powders showed that the samples can be efficiently excited by near UV and blue LEDs. Upon excitation at 448 nm, the emission spectra of all these samples showed two bands centred at 485 (blue) and 585 nm (yellow) which corresponds to the 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of Dy3+ ion, respectively. Intensity of blue emission was found to be stronger than the yellow emission in all the three samples. Integrated yellow to blue (Y/B) emission intensity was found to be increased with increasing the Ga content in the present YAGG host. Therefore, concentration (0.1, 1.0, 2.0 and 4.0 mol%) of Dy3+ ions was varied in the Ga rich (Y3Ga4AlO12) nano-powder. The chromaticity co-ordinates of all the prepared nano-powders were located in the white light region and also found to be dependent on Dy3+ ion concentration and excitation wavelength. The decay curves for 4F9/2 level of Dy3+ ion exhibited non-exponential nature in all the studied samples and the lifetime values remained constant (~1.0 ms) with increasing the Ga content, but were found to decrease with increasing the Dy3+ ion concentration. The results indicated that 2.0 mol% of Dy3+-doped Y3Ga4AlO12 nano-powder under 352 nm excitation is suitable for the white light emitting device applications.