Resonance/off-resonance excitations: implications on the thermal evolution of Eu3+ photoluminescence

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 11; no. 18; pp. 6095 - 6106
• Main Authors: De, Arnab, Hernández-Rodríguez, Miguel A, Carneiro Neto, Albano N, Dwij, Vivek, Sathe, Vasant, Carlos, Luís D, Ranjan, Rajeev
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 11.05.2023
• Subjects: Cooling; Erbium; Europium; Excitation; Light emission; Phosphors; Photoluminescence; Resonance; Temperature dependence; Thermal evolution
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d2tc03464f

Generally, it is known that the intensity of the emission of trivalent lanthanide ions (Ln3+) 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 7F0 and 7F1 ground states in populating the 5D0 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 (Sr = 4.9% K−1) at 83 K. This performance is due to the definition of a thermometric parameter involving the intensity ratio of the 5D0 → 7F2 (Eu3+) and 4S3/2 → 4I15/2 (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.