Observation of multi-mode: Upconversion, downshifting and quantum-cutting emission in Tm3+/Yb3+ co-doped Y2O3 phosphor

Upconversion luminescence based temperature sensing properties and anti-counterfeiting applications of GdNbO4:Tm3+/Yb3+ phosphor

Pure monoclinic phase GdNbO4:Tm3+/Yb3+ phosphor was prepared using solid state reaction method for upconversion emission, optical thermometry, latent fingerprints visualization and anti-counterfeiting applications. The prepared phosphor exhibits colour tunability with temperature variation (from blue to almost white) and good suppression of thermal quenching. The temperature sensing characteristic from thermally and non-thermally coupled levels of Tm3+ ion were investigated using the fluorescence intensity ratio (FIR) approach. The result shows that the sensitivity for non-thermally coupled level is about ∼ 45 times higher than thermally coupled level. Latent fingerprint detection on various surfaces and anti-counterfeiting ink application were also shown upon 980 nm laser diode excitation. Above results indicate that the prepared GdNbO4:Tm3+/Yb3+ phosphor have applicability in the field of frequency upconversion, optical thermometry, color tunable devices, latent fingerprint visualization and anti-counterfeiting applications.

The Coming of Age of Neodymium: Redefining Its Role in Rare Earth Doped Nanoparticles

Among luminescent nanostructures actively investigated in the last couple of decades, rare earth (RE³⁺) doped nanoparticles (RENPs) are some of the most reported family of materials. The development of RENPs in the biomedical framework is quickly making its transition to the ∼800 nm excitation pathway, beneficial for both in vitro and in vivo applications to eliminate heating and facilitate higher penetration in tissues. Therefore, reports and investigations on RENPs containing the neodymium ion (Nd³⁺) greatly increased in number as the focus on ∼800 nm radiation absorbing Nd³⁺ ion gained traction. In this review, we cover the basics behind the RE³⁺ luminescence, the most successful Nd³⁺-RENP architectures, and highlight application areas. Nd³⁺-RENPs, particularly Nd³⁺-sensitized RENPs, have been scrutinized by considering the division between their upconversion and downshifting emissions. Aside from their distinctive optical properties, significant attention is paid to the diverse applications of Nd³⁺-RENPs, notwithstanding the pitfalls that are still to be addressed. Overall, we aim to provide a comprehensive overview on Nd³⁺-RENPs, discussing their developmental and applicative successes as well as challenges. We also assess future research pathways and foreseeable obstacles ahead, in a field, which we believe will continue witnessing an effervescent progress in the years to come.

Manipulating the Injected Energy Flux via Host-Sensitized Nanostructure for Improving Multiphoton Upconversion Luminescence of Tm3

Combating the concentration quenching effect by increasing the concentration of sensitized rare-earth ions in rational design upconversion nanostructure will make it easier to utilize injection energy flux and transfer it to emitters, resulting in improved upconversion luminescence (UCL). We proposed a host-sensitized nanostructure (active core@luminescent shell@inert shell) to improve multiphoton UCL of Tm³⁺ based on the LiLnF₄ host. Yb³⁺ ions were isolated in the core as energy absorbents, and Tm³⁺ was doped in the interior LiYbF₄ host shell. Compared with sandwich structured nanocrystals (Y@Y:Yb/Tm@Y), reverse structure (YbTm@Yb@Y), and fully doped structure (YbTm@YbTm@Y), the proposed structure achieved the highest efficiency of multiphoton UCL and favored a better FRET-based application performance as the Tm³⁺ located at an optimized spatial distribution. Furthermore, steady-state and dynamic analysis results demonstrate that by manipulating the spatial distribution of the active ions, excited energy can be tuned to enable multiphoton upconversion enhancement, overcoming the conventional limitations.

Promising lanthanide-doped BiVO4 phosphors for highly efficient upconversion luminescence and temperature sensing

The semiconductor oxide BiVO₄ has been intensively studied as a highly efficient photocatalyst. Here we attempt to adopt trivalent lanthanide (Ln³⁺)-doped BiVO₄ as a novel upconversion luminescence (UCL) material for achieving high-efficiency UCL and temperature sensing under near-infrared (NIR) irradiation. Er³⁺/Tm³⁺, Yb³⁺/Er³⁺, and Yb³⁺/Tm³⁺ ions were selected to co-dope the BiVO₄ phosphors, achieving three primary colors of red, green, and blue (RGB) with high color-purity. At an optimal doping concentration, the upconversion quantum yield of the BiVO₄:8%Yb³⁺,18%Er³⁺ phosphor reaches as high as 2.9%. Furthermore, we, for the first time, demonstrate the non-contact temperature sensing properties of a BiVO₄:Er³⁺,Tm³⁺ phosphor via employing fluorescence intensity ratio technology. The results show that the maximum absolute thermal sensitivity is ≈70 × 10^-4 K^-1 at 473 K under 980 nm excitation, with high and stable sensitivity of more than 60 × 10^-4 K^-1 over a wide temperature range of 333-493 K. In addition, at a much safer wavelength of 1550 nm, this sample achieves maximum absolute sensitivity of 56 × 10^-4 K^-1 at 453 K. Moreover, the BiVO₄:Er³⁺,Tm³⁺ phosphor presents high relative sensitivity of about 1.1% K^-1 under both 980 and 1550 nm excitation at 293 K. These results indicate that the BiVO₄ semiconductor oxide can be used as a novel host to achieve high UCL efficiency and promising thermal sensing performance, suggesting potential applications in the new fields of anti-counterfeiting, displays, and non-contact temperature sensors.

Understanding and tuning blue-to-near-infrared photon cutting by the Tm3+/Yb3+ couple

Lanthanide-based photon-cutting phosphors absorb high-energy photons and 'cut' them into multiple smaller excitation quanta. These quanta are subsequently emitted, resulting in photon-conversion efficiencies exceeding unity. The photon-cutting process relies on energy transfer between optically active lanthanide ions doped in the phosphor. However, it is not always easy to determine, let alone predict, which energy-transfer mechanisms are operative in a particular phosphor. This makes the identification and design of new promising photon-cutting phosphors difficult. Here we unravel the possibility of using the Tm³⁺/Yb³⁺ lanthanide couple for photon cutting. We compare the performance of this couple in four different host materials. Cooperative energy transfer from Tm³⁺ to Yb³⁺ would enable blue-to-near-infrared conversion with 200% efficiency. However, we identify phonon-assisted cross-relaxation as the dominant Tm³⁺-to-Yb³⁺ energy-transfer mechanism in YBO₃, YAG, and Y₂O₃. In NaYF₄, in contrast, the low maximum phonon energy renders phonon-assisted cross-relaxation impossible, making the desired cooperative mechanism the dominant energy-transfer pathway. Our work demonstrates that previous claims of high photon-cutting efficiencies obtained with the Tm³⁺/Yb³⁺ couple must be interpreted with care. Nevertheless, the Tm³⁺/Yb³⁺ couple is potentially promising, but the host material-more specifically, its maximum phonon energy-has a critical effect on the energy-transfer mechanisms and thereby on the photon-cutting performance.

Photon-conversion and sensitization evaluation of Eu³⁺ in a borate glass system

Photon conversion is exhibited in a borate (LKZBSB) glass system containing Eu(3+), and the enhanced characteristic emissions of Eu(3+) with the codoping of Ce(3+) have been verified. A large Judd-Ofelt intensity parameter Ω2 of Eu(3+) indicates a high asymmetrical and strong covalent environment around rare-earth (RE) ions in LKZBSB glasses and spontaneous emission probability and a maximum emission cross section of the dominant 5D0→7F2 transition were derived to be 370  s(-1) and 1.28×10(-21)  cm2, respectively, revealing the potential UV→visible photon-conversion capacity of Eu(3+). Absolutely quantitative evaluation illustrates that Eu(3+) is a favorable photon-conversion center to achieve high photon-conversion efficiency. The addition of Ce(3+) is beneficial to realizing effective red emission of Eu(3+), which possesses commercial value by decreasing the dopant of expensive europium compounds. As an expectation, this photon-conversion LKZBSB glass system can promote the development of a photon downconversion layer for solar cells, which are particularly used in outer space with intense UV radiation.

Down shifting and quantum cutting from Eu3+, Yb3+ co-doped Ca12Al14O33 phosphor: a dual mode emitting material

We report the quantum cutting (QC) in a Eu³⁺, Yb³⁺ co-doped Ca₁₂Al₁₄O₃₃ phosphor synthesized through combustion method.

Intrinsic optical bistability and frequency upconversion in Tm3+–Yb3+-codoped Y2WO6 phosphor

Intrinsic optical bistability (IOB) behaviour in the Tm³⁺–Yb³⁺ codoped Y₂WO₆ phosphor.

Red and near infrared persistent luminescence nano-probes for bioimaging and targeting applications

Schematic representation of the different processes in persistent luminescence: charging (1), stimulation (2), discharging (3) (PET-persistent energy transfer, QT-quantum tunneling).