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Luminescence Nanothermometry
Published in Klaus D. Sattler, 21st Century Nanoscience – A Handbook, 2020
Oleksandr A. Savchuk, Joan J. Carvajal
Another characteristic of Ln3+ ions is that several of them have electronic excited states that are defined by the same or a very close energy value. This match of energy allows the transfer of energy from one ion to another as long as in one of them the excited state is populated while in the other is not, and will use this energy transfer process to promote an electron from the ground state to the excited state, from which light can be emitted. These energy transfer processes can occur between Ln3+ of the same kind (energy migration). They can also occur between lanthanide ions of different kinds, where the ion that absorbs the energy and transfers it to the other one is called the sensitizer, and the one that gets this energy and generates the final emission is called the activator. Also, the same process can occur between populated excited states if the lifetime of the starting state is long enough to allow these processes to occur. In these cases in which the originally populated state of the activator is not the ground state, it will end up with a populated electronic state that has a higher energy than any of the starting states. Thus, a radiative relaxation from this excited state to the ground state will generate a photon of higher energy than the excitation photons, a process known as upcon-version, and the mechanism that generates it is known as energy transfer upconversion (ETU) and is represented in Figure 25.14a.
Thermal Annealing and Doping Induced Tailoring of Phase and Upconversion Luminescence of NaYF4:Yb Er Microcrystals
Published in Nanoscale and Microscale Thermophysical Engineering, 2022
Shivanand H. Nannuri, Sana Adnan, Subash C K, Santhosh C, Sajan D. George
The steady-state fluorescence of the 3 mol% Mn2+ ions doped UC particles is shown in Figure 7), and the energy level diagram of the sample is represented in Figure 7. The emission spectrum shows three characteristic peaks corresponding to , , and transition of Er3+ ions, with dominant red emission as compared to green emission [42, 43]. In the case of upconversion luminescence particles, the sharp emission bands originate from the intraband f-f transition in the 4 f states that is shielded by 5s and 5p shells [44]. The underlying physical origin of the upconversion luminescence is attributed to many processes such as excited-state absorption (ESA), energy transfer upconversion (ETU), cooperative sensitization upconversion (CSU), energy migration-mediated upconversion (EMU) [45].