Temperature sensing based on the 4F7/2/4S3/2 - 4I15/2 upconversion luminescence intensity ratio in NaYE4:Er3+/Yb3+ nanocrystals

Different from the popular H-2(11/2)/S-4(3/2)-I-4(15/2) emission bands of Er3+, here we demonstrate for the first time the temperature detecting ability of the F-4(7/2)/S-4(3/2)- - I-4(15/2) transitions of Er3+ embedded in NaYF4 nanocrystals via luminescent ratiometric method. Following the NIR irradiation at 980 nm, the characteristic H-2(11/2)/S-4(3/2) - I-4(15/2) transitions of Er3+, and the F-4(7/2)-I-4(15/2) emission line that is rarely studied are successfully detected. The F-4(7/2)/H-2(11/2)/S-4(3/2) excited states are found to own the same lifetime. By studying on the temperature dependent upconversion luminescence, the F-4(7/2)/S-4(3/2) states, and the H-2(11/2)/S-4(3/2) ones are both confirmed to be thermally coupled. The luminescence intensity ratio between each pair of states thus could be used for thermal sensing. Using the F-4(7/2)/(S3/2I15/2)-S-4-I-4 emission bands could achieve a larger relative sensitivity than the traditional H-2(11/2)/S-4(3/2)-I-4(15/2) ones in the range of 332-483 K. Therefore, our work proposes a promising candidate for temperature measurement, which may find its application in the future.