Upconversion mechanisms in Er3+-doped Ba2YCl7

Efficient near infrared to visible upconversion luminescence is reported in the low phonon-energy host material Ba2YCl7:x% Er3+ (x=1, 10, 100). The upconversion mechanisms upon I-4(9/2) excitation (approximate to 800 nm) are investigated by means of excitation and time-resolved luminescence spectroscopy. H-2(9/2) is found to be populated by energy transfer upconversion and excited-state absorption, depending on the excitation energy. Characteristic excited-state absorption peaks in the excitation spectra a are used as a fingerprint to determine the population mechanisms for the other states with high luminescence intensities: S-4(3/2)/H-2(11/2), F-4(9/2), and (4)G(11/2). The assignment is confirmed by temperature, concentration, power, and time-dependent measurements. The relative intensities are accounted for by a Judd-Ofelt analysis.