resumo
Generally, it is known that the intensity of the emission of trivalent lanthanide ions (Ln(3+)) increases on cooling because of the reduced decay of the excited state population via phonon-mediated nonradiative transitions. In contrast to this, some studies in the recent past have shown that the intensity of Eu3+ photoluminescence decreases dramatically on cooling. While this anomalous behaviour has been found to be useful for designing highly sensitive luminescence thermometers, the mechanism underlying this anomalous behaviour remains elusive. Here, we address this issue using a combined experimental and theoretical approach. We identified off-resonance excitation as the exclusive factor which enhances the Eu3+ emissions with the increase of temperature. We could tune the temperature dependence of the Eu3+ light-emission by varying the bandpass of the excitation source around the off-resonance energy. Using kinetic rate equations, we model the temperature trend of the Eu3+ emission intensity in the steady state by considering the independent contribution of the F-7(0) and F-7(1) ground states in populating the D-5(0) excited state. As an illustrative example, we apply this understanding to designing an Er3+/Eu3+ codoped CaTiO3 phosphor that shows a considerably large relative thermal sensitivity (S-r = 4.9% K-1) at 83 K. This performance is due to the definition of a thermometric parameter involving the intensity ratio of the D-5(0) -> F-7(2) (Eu3+) and S-4(3/2) -> I-4(15/2) (Er3+) transitions in which the intensity of the former increases with the increase of the temperature while that of the latter shows the opposite temperature dependence.
palavras-chave
UP-CONVERSION LUMINESCENCE; EXCITED-STATE ABSORPTION; ASSISTED ENERGY-TRANSFER; MULTIPHONON RELAXATION; INTENSITY PARAMETERS; TEMPERATURE; THERMOMETRY; NANOCRYSTALS; COMPLEXES; IONS
categoria
Materials Science; Physics
autores
De, A; Hernández-Rodríguez, MA; Neto, AC; Dwij, V; Sathe, V; Carlos, LD; Ranjan, R
nossos autores
Albano Neto Carneiro Neto
Investigador Júnior
Luís Carlos
Professor Catedrático
Miguel Andrés Hernández Rodríguez
Investigador JúniorProjectos
CICECO - Aveiro Institute of Materials (UIDB/50011/2020)
CICECO - Aveiro Institute of Materials (UIDP/50011/2020)
Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)
agradecimentos
R. R. acknowledges the Science and Engineering Research Board (SERB) of the Ministry of Science and Technology (CRG/2021/000134), Government of India, for financial support. A. D. acknowledges the Department of Science and Technology (DST), Government of India, for the award of Inspire fellowship (IF1508850). CeNSE, IISc is acknowledged for the Raman and photoluminescence measurements. This work was also developed within the scope of the projects CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, and The Shape of Water (PTDC/NAN-PRO/3881/2020) financed by Portuguese funds through the FCT/MCTES(PIDDAC).