Unravelling the UV luminescence of Bi-doped LiYGeO4: a journey from first principles to temperature-dependent photoluminescence

resumo

Materials exhibiting persistent luminescence (PersL) have garnered attention due to their unique ability to emit light for extended periods after the excitation stops. LiYGeO4 has arisen as a promising host for PersL due to its notable defect abundance. When doped with Bi, it can provide a long-lasting ultraviolet emission, which may find interesting applications in areas such as photodynamic therapy or self-sustained photocatalysis. In the present paper, undoped and Bi-doped LiYGeO4 (0.5 mol%) samples were synthesized by solid-state reaction. X-ray diffraction confirmed the presence of the LiYGeO4 phase, alongside residual yttrium germanate phases. Additionally, we calculated its previously undocumented band structure using hybrid density functional theory to provide new theoretical insights. These calculations indicate that LiYGeO4 has a direct bandgap at the Gamma point, further supported by the absorption data. Elemental analyses allowed quantification of the samples, identifying the loss of Li during the synthesis. Room temperature (RT) photoluminescence (PL) showed a strong emission band peaked around 350-360 nm. Despite the extensive research conducted on LiYGeO4:Bi, the mechanisms underlying the PersL phenomenon remain unclear. To address this, we conducted temperature-dependent PL from 17 K to RT, using a 325 nm photon excitation. We propose that, at RT, the observed emission arises from the overlap of the 3P(1)1 -> 1S0 and 3P(2)1 -> 1S0 Bi3+ intraionic transitions, sublevels of the 3P1 state, which is completely split under the local crystal field generated by the ion environment. However, at cryogenic temperatures, the 3P0 -> 1S0 transition is the dominant one. Moreover, PersL emission was achieved for nearly 7 h, with 250 nm photon excitation for 10 min, arising from a contribution of the overlapped 3P(1)1 -> 1S0 and 3P(2)1 -> 1S0 transitions.

palavras-chave

PERSISTENT LUMINESCENCE; ENERGY-TRANSFER; Y2GEO5 BI3+; EU3+; SPECTROSCOPY; TB3+; ION

categoria

Materials Science; Physics

autores

Proença, I; Gouveia, JD; Girao, AV; Peres, M; Mateus, R; Alves, LC; Esteves, DM; Rodrigues, AL; Dias, MI; Lorenz, K; Rino, L; Costa, FM; Monteiro, T; Rodrigues, J

Grupos

G3 - Materiais Eletroquímicos, Interfaces e Revestimentos
G6 - Materiais Virtuais e Inteligência Artificial

Projectos

Collaboratory for Emerging Technologies, CoLab (EMERGING TECHNOLOGIES)

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

This research was funded by National funds through the FCT - Portuguese Foundation for Science and Technology under the i3N project UIDB/50025/2020 & UIDP/50025/2020 & LA/P/0037/2020 and project 2023.00054.RESTART. This work was also developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 (DOI 10.54499/UIDB/50011/2020), UIDP/50011/2020 (DOI 10.54499/UIDP/50011/2020) & LA/P/0006/2020 (DOI 10.54499/LA/P/0006/2020), financed by national funds through the FCT/MCTES (PIDDAC). J. Rodrigues acknowledges FCT for Programme Stimulus of Scientific Employment Support, grants 2022.00010.CEECIND and CEECINSTLA/00005/2022, J. D. Gouveia acknowledges the FCT grant 2023.06511.CEECIND, in the scope of the Individual Call to Scientific Employment Stimulus - 6th Edition, and D. M. Esteves acknowledges FCT for the PhD grant 2022.09585.BD (DOI: 10.54499/2022.09585.BD). The authors thank MSc Celeste Azevedo and M. R. Soares (CICECO - Aveiro Institute of Materials) for the diffuse reflectance and XRD experiments, respectively. Acknowledgements are also due to the project 101217446 POEMS, which is supported by the Chips Joint Undertaking and its members, including top-up funding by FCT.