Photon Upconversion Spectroscopy
405
used the SMILES pattern for encoding and decoding together with time-gated luminescence see Fig. 9d. They further loaded the core shell nanoparticles on a rotating
plate under 980 nm illuminations. They tracked the trajectory of rotated nanoparticles via its upconversion luminescence, and the tailing length is well correlated with
the decay rate see Fig. 9e. Thus, blue UC in Tm/Yb system has been used for several
applications.
4 Conclusion
In conclusion, this chapter describes photon upconversion spectroscopy technique
in detail. Introduction section gives a clear distinction among two-photon absorption (TPA), second-harmonic generation (SHG), and photon upconversion processes
of a non-linear emission. Photon upconversion is different from TPA and SHG
processes as it is observed through the involvement of sequential absorption of
photons between real stationary states. Due to the involvement of real stationary
states, a very low laser power (few mW) in continuous wave mode can be used
to achieve photon upconversion emission. In addition to this, different mechanisms
of photon upconversion process, such as excited state absorption (ESA) process,
energy transfer upconversion (ETU), co-operative energy transfer (CET) process,
phonon assisted upconversion and cross relaxation process, have also been explained
at length.
Since, lanthanide ions doped in different host matrices have been identified most
suitable activator to achieve photon upconversion emission, therefore, energy transfer
process in lanthanides have also been covered. Photon upconversion like emission
is also achieved in organic molecules but through triplet–triplet annihilation (TTA)
process. Therefore, a short description of the mechanism of TTA has also been
covered for the comprehensiveness of information in the area. Further, after a detailed
description of theoretical aspect, a brief description of the experimental setup and its
working has been covered so that a beginner in this area can also design fundamental
experiments.
Two model systems, Er/Yb and Tm, Yb doped in different hosts have been taken to
represent and explain NIR to visible and NIR to NIR upconversion emission. A detail
description of upconversion emission, its mechanism and different applications have
been discussed in both the systems. It can be concluded that the photon upconversion
spectroscopy is a versatile, easy and highly useful technique for bio-imaging, sensing,
lighting and display, security applications, etc.
References
1. J. Yu, Y. Cui, H. Xu , Y. Yang, Z. Wang, B. Chen, G. Qian, Nat. Commun. 4, 2719–2725 (2013)
2. K.E. Sapsford, T. Pons, I.L. Medintz, H. Mattoussi, Sensors 6, 925–953 (2006)
405
used the SMILES pattern for encoding and decoding together with time-gated luminescence see Fig. 9d. They further loaded the core shell nanoparticles on a rotating
plate under 980 nm illuminations. They tracked the trajectory of rotated nanoparticles via its upconversion luminescence, and the tailing length is well correlated with
the decay rate see Fig. 9e. Thus, blue UC in Tm/Yb system has been used for several
applications.
4 Conclusion
In conclusion, this chapter describes photon upconversion spectroscopy technique
in detail. Introduction section gives a clear distinction among two-photon absorption (TPA), second-harmonic generation (SHG), and photon upconversion processes
of a non-linear emission. Photon upconversion is different from TPA and SHG
processes as it is observed through the involvement of sequential absorption of
photons between real stationary states. Due to the involvement of real stationary
states, a very low laser power (few mW) in continuous wave mode can be used
to achieve photon upconversion emission. In addition to this, different mechanisms
of photon upconversion process, such as excited state absorption (ESA) process,
energy transfer upconversion (ETU), co-operative energy transfer (CET) process,
phonon assisted upconversion and cross relaxation process, have also been explained
at length.
Since, lanthanide ions doped in different host matrices have been identified most
suitable activator to achieve photon upconversion emission, therefore, energy transfer
process in lanthanides have also been covered. Photon upconversion like emission
is also achieved in organic molecules but through triplet–triplet annihilation (TTA)
process. Therefore, a short description of the mechanism of TTA has also been
covered for the comprehensiveness of information in the area. Further, after a detailed
description of theoretical aspect, a brief description of the experimental setup and its
working has been covered so that a beginner in this area can also design fundamental
experiments.
Two model systems, Er/Yb and Tm, Yb doped in different hosts have been taken to
represent and explain NIR to visible and NIR to NIR upconversion emission. A detail
description of upconversion emission, its mechanism and different applications have
been discussed in both the systems. It can be concluded that the photon upconversion
spectroscopy is a versatile, easy and highly useful technique for bio-imaging, sensing,
lighting and display, security applications, etc.
References
1. J. Yu, Y. Cui, H. Xu , Y. Yang, Z. Wang, B. Chen, G. Qian, Nat. Commun. 4, 2719–2725 (2013)
2. K.E. Sapsford, T. Pons, I.L. Medintz, H. Mattoussi, Sensors 6, 925–953 (2006)