The role of lanthanide luminescence in advancing technology

Abstract

Our society is indebted to the numerous inventors and scientists who helped bring about the incredible technological advances in modern society that we all take for granted. The importance of knowing the history of these inventions is often underestimated, although our reliance on technology is escalating. Lanthanide luminescence has paved the way for many of these inventions, from lighting and displays to medical advancements and telecommunications. Given the significant role of these materials in our daily lives, knowingly or not, their past and present applications are reviewed. A majority of the discussion is devoted to pointing out the benefits of using lanthanides over other luminescent species. We aimed to give a short outlook outlines promising directions for the development of the considered field. This review aims to provide the reader enough content to further appreciate the benefits that these technologies have brought into our lives, with the perspective of travelling among the past and latest advances in lanthanide research, aiming for an even brighter future.

Fig. 1. (a) 1931 Commission Internationale de l'éclairage (CIE) diagram and corresponding positions of Eu³⁺ and Tb³⁺-doped phosphors as a function of colour temperature and purity. The inset shows a white light phosphor under UV excitation at 254 nm. (b) The range of emission colours achieved by doping β-YBiB₃O₆ with different amounts of Tb³⁺ (top) and Eu³⁺ (bottom) under 254, 310 and 365 nm UV wavelengths. Reproduced with permission from ref. 29.

Fig. 2. (A) Original schematic of the Nd:YAG laser in the 1964 patent filed by Geusic and Van Uitert. (B) Photograph of the NeuroBlate® system by Monteris, which uses a Nd:YAG laser at 1064 nm for stereotactic laser ablation in neurosurgery. (C) Graphical depiction of the various ways infrared lasers are used in LIDAR and free space optical communication. Figures reprinted from ref. 55 and 82 with appropriate permissions.

Fig. 3. Scintillators are commercially utilized in the form of crystalline arrays, single crystals, and polycrystalline screens. The most prominent lanthanide activators for such materials are Ce³⁺, Eu^2+/3+, Pr³⁺, Tb³⁺ and Tm³⁺. The emissions from these activator ions can be classified by fast decay times (in the ns to ps range) for the allowed 5d → 4f transitions, or by slower decay times in the μs to ms range from the forbidden 4f → 4f transitions.

Fig. 4. (A) Schematic of the principle of a computed tomography (CT) scanner. The rotating scintillation detector array shown is a GE Gemstone array. Detector photograph courtesy of GE. (B) Schematic of a positron emission tomography (PET) scanner. The scintillation detector array shown is a 13 × 13 LSO:Ce³⁺ array. Each scintillator crystal is 4 mm in diameter. (C) CT (top), PET (bottom) and combined PET/CT (middle) images of a mouse bearing a tumor. GE array. LSO detector array photographs and mouse imaging photographs modified from ref. 157.

Fig. 5. Banknotes and documents from several countries (Left) photographed under ambient lighting, (Center) photographed under UV lamp irradiation (λ_max: 365 nm) and (Right) recorded emission spectra of the various observed phosphors. Chosen documents (from top to bottom) are 10 Chinese yuan, 50 000 Colombian pesos, 10 euro, 500 Indian rupees, 100 Nigerian naira, 20 Swiss francs, and a visa page from the Canadian passport.

Fig. 6. Map of the submarine telecommunications cables around the world as of 2023. Reproduced from https://www.submarinecablemap.com/.

Fig. 7. Energy level diagrams of Er³⁺ and Pr³⁺ depicting the excitation and emission wavelengths relevant for their use in optical amplifiers.

Fig. 8. Solar energy conversion technologies using lanthanides. The solar irradiance spectrum (top) and corresponding regions of wavelengths where upconversion, quantum cutting and downshifting can be harnessed. Inset shows the mechanisms relevant to each of the luminescence mechanisms. On the bottom, there are graphical depictions of luminescent solar concentrators (left), photovoltaic conversion layers and films (middle) and photovoltaic cells doped with lanthanides directly into the semiconductor layer.

Fig. 9. Summary scheme depicting the phosphors and materials mentioned throughout this review.