The role of Cr 3+ and Cr 4+ in emission brightness enhancement and sensitivity improvement of NIR-emitting Nd 3+ /Er 3+ ratiometric luminescent thermometers

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2021-09, Vol.9 (37), p.12671-12680
• Main Authors: Piotrowski, W., Dalipi, L., Szukiewicz, R., Fond, B., Dramicanin, M., Marciniak, L.
• Format: Article
• Language: English
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/D1TC03046A

Despite the numerous advantages of lanthanide based luminescent thermometers, a major limitation is the limited brightness associated with the low absorption cross section of the 4f–4f transitions. In this paper, co-doping with Cr 3+/4+ is proposed as a strategy to enhance the near-infrared luminescence emission of Nd 3+ /Er 3+ -based luminescent thermometers, as well as to modulate the temperature sensitivity of the ratio of Nd 3+ to Er 3+ in YAG microcrystals. It was found that an increase in the Cr 3+ concentration leads to the enhancement of the YAG:Nd 3+ ,Er 3+ emission intensity via the Cr 3+ → Ln 3+ sensitization process. The quantitative analysis of the absolute brightness indicates the 30-fold enhancement of their near infrared emission upon broad white light excitation for 20% Cr 3+ with respect to the non co-doped with the Cr 3+ counterpart. In addition, the phonon-assisted nature of the simultaneously occurring Cr 3+ → Ln 3+ and Nd 3+ → Cr 4+ → Er 3+ energy transfers leads to a 7-fold increase of the relative temperature sensitivity of the ratio of Nd 3+ to Er 3+ emission. In conclusion, co-doping with transition metals can enhance simultaneously the luminescence brightness and the temperature sensitivity of NIR luminescent thermometers, holding promise for sensitive and robust remote temperature sensing at physiological temperatures.