The role of Cr3+ and Cr4+ in emission brightness enhancement and sensitivity improvement of NIR-emitting Nd3+/Er3+ ratiometric luminescent thermometers

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2021-10, Vol.9 (37), p.12671-12680
• Main Authors: Piotrowski, W, Dalipi, L, Szukiewicz, R, Fond, B, Dramicanin, M, Marciniak, L
• Format: Article
• Language: English
• Subjects: Absorption cross sections; Brightness; Doping; Emission analysis; Erbium; Luminescence; Microcrystals; Near infrared radiation; Remote sensing; Sensitivity enhancement; Temperature; Thermometers; Transition metals; Trivalent chromium; White light
• 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 Cr3+/4+ is proposed as a strategy to enhance the near-infrared luminescence emission of Nd3+/Er3+-based luminescent thermometers, as well as to modulate the temperature sensitivity of the ratio of Nd3+ to Er3+ in YAG microcrystals. It was found that an increase in the Cr3+ concentration leads to the enhancement of the YAG:Nd3+,Er3+ emission intensity via the Cr3+ → Ln3+ 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% Cr3+ with respect to the non co-doped with the Cr3+ counterpart. In addition, the phonon-assisted nature of the simultaneously occurring Cr3+ → Ln3+ and Nd3+ → Cr4+ → Er3+ energy transfers leads to a 7-fold increase of the relative temperature sensitivity of the ratio of Nd3+ to Er3+ 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.