Infrared and visible emission of Er 3+ in combustion-synthesized CaAl 2O 4 phosphors

Abstract

New near-infrared luminescent, monoclinic CaAl 2O 4:Er 3+ phosphor was prepared by using the combustion route at furnace temperatures as low as 500 °C in a few minutes. Combustion synthesized phosphor has been well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX) mapping studies. The luminescence spectra of Er 3+-doped calcium aluminate were studied at UV (380 nm), vis (488 nm) and IR (980 nm) excitation. Upon UV and vis excitation, the CaAl 2O 4:Er 3+ phosphor exhibits emission bands at ~523 nm and at ~547 nm, corresponding to transitions from the 2H 11/2 and 4S 3/2 erbium levels to the 4I 15/2 ground state. A strong luminescence at 1.55 μm in the infrared (IR) region due to 4I 13/2→ 4I 15/2 transition has been observed in CaAl 2O 4:Er 3+ phosphor upon 980 nm CW pumping. In the spectrum of IR-excited up-conversion luminescence, green (~523 and ~547 nm) and red (662 nm) luminescence bands were present, the latter associated with the 4F 9/2→ 4I 15/2 transitions of Er 3+ ions. Both excited state absorption and energy transfer may be proposed as processes responsible for the population of the 4S 3/2 and 4F 9/2 erbium levels upon IR excitation. The mechanisms responsible for the up-conversion luminescence are discussed.