Photoluminescence properties of Tm3+/Ho3+/Cr3+-co-doped Y3AlGa4O12nano-garnet phosphors for visible-NIR LED applications

Trivalent lanthanide (Ln3+; Ln = Tm, Ho, Cr)-doped Y3AlGa4O12nano-garnet phosphor powders with varying Cr3+ ion concentration (0.5, 1.0, 2.0 and 3.0 mol%) were prepared using sol-gel synthesis. The prepared powders were characterized by X-ray powder diffraction (XRD), Raman spectroscopic and photoluminescence spectroscopic techniques. Phase purity, structure and crystallite size have been estimated from the XRD results. Raman spectra showed the vibrational analysis of the prepared powders. Excitation spectrum showed a broad band at 354 nm when monitored at 712 nm. Under 360 nm excitation, emission spectrashowed a broad band with characteristic peaks of Tm3+, Ho3+ and Cr3+ ions. The intensity of peaks and full width at half maximum were increased up to 2.0 mol% Cr3+ ion and then decreased. All the decay curves exhibited non-exponential nature with an average lifetime of 0.302 ms. The decay curves were found to be insensitive to the Cr3+ ion concentration. The CIE colour co-ordinates were located in the orange-red region of the CIE diagram with correlated colour temperature 2261 K. The results showed that the present phosphors were suitable for the solidstate light emitting diode applications.