Photon upconversion in trivalent erbium ions

TY - BOOK

T1 - Photon upconversion in trivalent erbium ions

AU - Christiansen, Jeppe

N1 - Forsvaret d. 28/1 2020

PY - 2020/1

Y1 - 2020/1

N2 - This PhD thesis reports on the experimental and theoretical investigation of 1500 nm to 980 nm photon upconversion in thin films of erbium-doped TiO2, which has applications in improving silicon-based solar cells through upconversion of sub-band-gap photons. Three main publications are included in this thesis reporting on: i) the development of a rate-equation model, ii) the upconversion-luminescence (UCL) dependence on the fabrication parameters, and iii) incorporating gold nanostructures for enhancing the upconversion efficiency through photonic enhancement.The developed rate-equation model can account for the UCL-intensity dependence over a broad dynamic range, and through the model, a new benchmark parameter -- the saturation intensity -- is introduced. The investigation on the fabrication process shows generally increased UCL yield with deposition temperature up to 350 C and that post-annealing treatment quenches the UCL yield. Through the study of photonic enhancement, an unprecedented 913(51)-fold enhancement of the UCL yield is measured at an intensity of 1.7 W/cm2. The results are compared to an extended version of the rate-equation model with a good qualitative agreement. Through the extended rate-equation model, it is possible to determine the concentration of the mean electromagnetic energy density in the upconverting films, which, together with the saturation intensity, allows for a justified prediction on the required steps before photonic-enhanced upconverters will see the light of day.The thesis concludes with an assessment of the developed rate-equation model through a comparison of measured and calculated external upconversion quantum yields with outstanding agreement assuming similar absorption strength, as reported in the literature. The assumption of an average energy-transfer rate in the rate-equation model is corroborated through calculation showing a strong coupling of the erbium ions. Lastly, an experiment is proposed for further investigations of the crucial upconversion parameter -- the energy-transfer rate.

AB - This PhD thesis reports on the experimental and theoretical investigation of 1500 nm to 980 nm photon upconversion in thin films of erbium-doped TiO2, which has applications in improving silicon-based solar cells through upconversion of sub-band-gap photons. Three main publications are included in this thesis reporting on: i) the development of a rate-equation model, ii) the upconversion-luminescence (UCL) dependence on the fabrication parameters, and iii) incorporating gold nanostructures for enhancing the upconversion efficiency through photonic enhancement.The developed rate-equation model can account for the UCL-intensity dependence over a broad dynamic range, and through the model, a new benchmark parameter -- the saturation intensity -- is introduced. The investigation on the fabrication process shows generally increased UCL yield with deposition temperature up to 350 C and that post-annealing treatment quenches the UCL yield. Through the study of photonic enhancement, an unprecedented 913(51)-fold enhancement of the UCL yield is measured at an intensity of 1.7 W/cm2. The results are compared to an extended version of the rate-equation model with a good qualitative agreement. Through the extended rate-equation model, it is possible to determine the concentration of the mean electromagnetic energy density in the upconverting films, which, together with the saturation intensity, allows for a justified prediction on the required steps before photonic-enhanced upconverters will see the light of day.The thesis concludes with an assessment of the developed rate-equation model through a comparison of measured and calculated external upconversion quantum yields with outstanding agreement assuming similar absorption strength, as reported in the literature. The assumption of an average energy-transfer rate in the rate-equation model is corroborated through calculation showing a strong coupling of the erbium ions. Lastly, an experiment is proposed for further investigations of the crucial upconversion parameter -- the energy-transfer rate.

KW - upconversion

KW - luminescent rare-earth ions

KW - improving silicon-based photovoltaics

M3 - Ph.D. thesis

BT - Photon upconversion in trivalent erbium ions

PB - Århus Universitet

CY - Aarhus

ER -