Cho, Youngho Song, Si Won Lim, Soo Yeong Kim, Jae Hun Park, Chan Ryang Kim, Hyung Min 2024-01-20T02:01:31Z 2024-01-20T02:01:31Z 2021-09-01 2017-03-14 1463-9076 https://pubs.kist.re.kr/handle/201004/122948 Although upconversion phosphors have been widely used in nanomedicine, laser engineering, bioimaging, and solar cell technology, the upconversion luminescence mechanism of the phosphors has been fiercely debated. A comprehensive understanding of upconversion photophysics has been significantly impeded because the number of photons incorporated in the process in different competitive pathways could not be resolved. Few convincing results to estimate the contribution of each of the two-, three-, and four-photon channels of near-infrared (NIR) energy have been reported in yielding upconverted visible luminescence. In this study, we present the energy upconversion process occurring in NaYF4: Yb3+, Er3+ phosphors as a function of excitation frequency and power density. We investigated the upconversion mechanism of lanthanide phosphors by comparing UV/VIS one-photon excitation spectra and NIR multi-photon spectra. A detailed analysis of minor transitions in one-photon spectra and luminescence decay enables us to assign electronic origins of individual bands in multi-photon upconversion luminescence and provides characteristic transitions representing the corresponding upconversion channel. Furthermore, we estimated the quantitative contribution of multiple channels with respect to irradiation power and excitation energy. English ROYAL SOC CHEMISTRY RARE-EARTH IONS MULTIPHONON RELAXATION UPCONVERTING NANOPARTICLES ENERGY-LEVELS LUMINESCENCE CORE NANOCRYSTALS TEMPERATURE INTENSITIES MECHANISM Spectral evidence for multi-pathway contribution to the upconversion pathway in NaYF4:Yb3+, Er3+ phosphors Article 10.1039/c7cp00048k 1 PHYSICAL CHEMISTRY CHEMICAL PHYSICS, v.19, no.10, pp.7326 - 7332 PHYSICAL CHEMISTRY CHEMICAL PHYSICS 19 10 7326 7332 scie scopus 000396148600046 2-s2.0-85015305309 Chemistry, Physical Physics, Atomic, Molecular & Chemical Chemistry Physics Article RARE-EARTH IONS MULTIPHONON RELAXATION UPCONVERTING NANOPARTICLES ENERGY-LEVELS LUMINESCENCE CORE NANOCRYSTALS TEMPERATURE INTENSITIES MECHANISM upconversion phosphors photophysics