Luminescence spectroscopy and near-infrared to visible upconversion of nanocrystalline Gd3Ga5O12:Er3+

The near-infrared to visible upconversion properties of nanocrystalline Gd3Ga5O12:Er3+ (I and 5%) were studied following excitation of the I-4(9/2) exited state with 800 nm radiation. Intense green and red emissions were observed from the (H-2(11/2), S-4(3/2)) --> I-4(15/2) and F-4(9/2) --> I-4(15/2) transitions, respectively. The upconverted decay times in the 1% sample were identical compared to those obtained with 488 nm excitation, indicating that ESA was responsible for populating the upper emitting states. However, as the Er3+ concentration was increased to 5%, the upconverted decay times were lengthened and deviated from exponentiality, indicating the presence of energy transfer upconversion. In addition, an enhancement of the red (F-4(9/2) --> I-4(15/2)) upconversion emission was observed in the 5% sample and occurred via an energy transfer process of the type (I-4(9/2), I-4(11/2)) --> (I-4(13/2), F-4(9/2)).