Competition between two- and three-photon upconversion in Er3+-doped microcrystals

• Published in: Journal of luminescence Vol. 227; p. 117542
• Main Authors: Mukhuti, Kingshuk, Adusumalli, Venkata N.K.B., Raj R., Kamal, Bansal, Bhavtosh, Mahalingam, Venkataramanan
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-11-2020
• Subjects: Multiphoton processes; Photoluminescence; Temperature dependence; Upconversion pathways; Temperature dependence; Upconversion pathways; Multiphoton processes; Photoluminescence
• ISSN: 0022-2313; 1872-7883
• DOI: 10.1016/j.jlumin.2020.117542

The emission spectrum of lanthanide-rich upconverters consists of optically or thermally excited transition bands involving different pathways. We investigate multiphoton processes in Yb3+–Er3+ codoped β−NaGdF4 to demonstrate that the emission from the phosphor involves both two- and three-photon mechanisms, where the sample temperature, and the laser excitation power play crucial roles in determining the leading pathway. The two-photon processes dominate at room temperature, and the effect of higher-order (three-photon) processes becomes increasingly important as the temperature is lowered. The Yb3+–Er3+ systems are reported to be among the best performing ratiometric luminescent thermometers in a very wide range. Our experimental findings demand a careful elimination of errors that may appear from the laser-induced heating of the sample and contributions from higher-order multiphoton processes when using such thermometers below room temperature.
•Multiphoton upconversion pathways are strongly temperature-dependent.•Room-temperature luminescence is mostly governed by two-photon mechanisms.•Higher order pathways become increasingly important at low temperatures.•Excitation power density plays a crucial role in determining the dominant pathway.