Zhongyi Wan

Dual-Phase Glass Ceramic: Structure, Dual-Modal Luminescence, and Temperature Sensing Behaviors

Yb(3+)/Er(3+)/Cr(3+) triply doped transparent bulk glass ceramic containing orthorhombic YF3 and cubic Ga2O3 nanocrystals was fabricated by a melt-quenching route to explore its possible application in optical thermometry with high spatial and temperature resolution. It was experimentally observed that Yb(3+)/Er(3+) ions incorporated into the precipitated YF3 nanophase, while Cr(3+) ions partitioned into the crystallized Ga2O3 nanophase after glass crystallization. Importantly, such spatial isolation strategy efficiently suppressed adverse energy transfer among different active ions. As a consequence, intense green anti-Stokes luminescence originated from Er(3+): (2)H11/2,(4)S3/2 → (4)I15/2 transitions, and deep-red Stokes luminescence transitions assigned to Cr(3+): (2)E → (4)A2 radiation were simultaneously realized. Impressively, the intermediate crystal-field environment for Cr(3+) in Ga2O3 made it possible for lifetime-based temperature sensing owing to the competition of radiation transitions from the thermally coupled Cr(3+) (2)E and (4)T2 excited states. In the meantime, the low-phonon-energy environment for Er(3+) in YF3 was beneficial for upconversion fluorescence intensity ratio-based temperature sensing via thermal population between the (2)H11/2 state and (4)S3/2 state. The Boltzmann distribution theory and the two-level kinetic model were adopted to interpret these temperature-dependent luminescence of Er(3+) and Cr(3+), respectively, which gave the highest temperature sensitivities of 0.25% K(-1) at 514 K for Er(3+) and 0.59% K(-1) at 386 K for Cr(3+).

Highly Sensitive Dual-Phase Nanoglass-Ceramics Self-Calibrated Optical Thermometer

A strategy to achieve high sensitivity of noncontact optical thermometer via the structure design of nanoglass-ceramic and the usage of Ln(3+) (Ln = Eu, Tb, Dy) luminescence as reference signal and Cr(3+) emission as temperature signal was provided. Specifically, the synthesized dual-phase glass-ceramics were evidenced to enable spatially confined doping of Ln(3+) in the hexagonal GdF3 nanocrystals and Cr(3+) in the cubic Ga2O3 nanoparticles, being beneficial to suppressing detrimental energy transfer between Ln(3+) and Cr(3+) and thus significantly enhancing their luminescence. As a consequence, completely different temperature-sensitive luminescence of Ln(3+)4f → 4f transition and Cr(3+) 3d → 3d transition in the present glass-ceramic resulted in obvious variation of Cr(3+)/Ln(3+) fluorescence intensity ratio with temperature and strikingly high detecting temperature sensitivity of 15-22% per K. We believe that this preliminary study will provide an important advance in exploring other innovative optical thermometry.

Large-scale room-temperature synthesis and optical properties of perovskite-related Cs4PbBr6 fluorophores

Currently, metal–halide perovskite semiconductors have attracted enormous attention for their excellent optical performance. However, challenging issues, such as the ability to perform large-scale synthesis as well as the thermal/moisture stability, limit their practical applications. Herein, we developed an inhomogeneous interface reaction strategy in a liquid–liquid immiscible two-phase system to realize the large-scale room temperature synthesis of novel perovskite-related Cs4PbBr6 semiconductors. Although the sizes were on the micrometer scale, the Cs4PbBr6 products exhibited bright green luminescence with a narrow line-width originating from exciton recombination confined in PbBr64− octahedra, and the photoluminescence quantum yields reached 40–45% owing to a large exciton binding energy of 222 meV. Furthermore, temperature cycling experiments demonstrated their excellent thermal stability with repeatable and reversible luminescence, and moisture-resistance experiments showed ∼65% of quantum yield loss after exposure to air for one month. Finally, a prototype white light-emitting diode device with a low correlated color temperature of 3675 K and a high color rendering index of 83 was constructed using green emissive Cs4PbBr6 and red emissive Eu2+:CaAlSiN3 phosphors, certainly indicating its promising applications in the optoelectronics field.

Tuning into blue and red: europium single-doped nano-glass-ceramics for potential application in photosynthesis

A series of SiO2–Al2O3–NaF–YF3 oxyfluoride glasses and β-YF3 nanocrystals embedded glass ceramics single-doped with europium ions were prepared by high-temperature melt-quenching to explore blue/red luminescent materials for potential application in the photosynthesis of green plants. Both Eu2+ and Eu3+ activators were demonstrated to coexist in this specially designed glass fabricated under ambient atmosphere, which can be well explained based on the optical basicity model of glass and evidenced by emission, excitation and time-resolved spectra. Furthermore, the crystallization strategy has been adopted to convert the precursor glasses into nano-glass-ceramics. As a result, Eu3+ ions partitioned into the precipitated orthorhombic YF3 nanophase, while Eu2+ ions remained in the glass matrix. Such spatial isolation of the different active ions in glass ceramics can effectively suppress adverse energy transfer between Eu2+ and Eu3+, leading to both intense Eu2+ blue and Eu3+ red emissions under ultraviolet light excitation.

Intense multi-state visible absorption and full-color luminescence of nitrogen-doped carbon quantum dots for blue-light-excitable solid-state-lighting

Currently, the excitation-wavelength-dependent photoluminescence of traditional carbon dots does not constitute true tuning and their absorptions show gradual attenuation in the visible region. Herein, we report a facile strategy to realize intense visible absorption and full-color emissions of nitrogen doped carbon dots via the control of surface nitriding. The quantum yields of the carbon dots in aqueous solution reached 49.2%, 30.6% and 30.3% for blue, yellow and red emissions, respectively. Structural characterizations and spectroscopic analyses verify that three diverse emitting states, i.e., sp2 carbon core, CO and CN related surface defects, are responsible for the multi-state absorptions and tunable emissions of the carbon dots. The ability to truly tune luminescence into the red wavelength region with strong visible absorption enables these carbon dots to improve the correlated color temperature and color rendering index of traditional phosphor-converted white light-emitting diodes.

Optical spectroscopy of Cr³⁺-doped transparent nano-glass ceramics for lifetime-based temperature sensing.

Transparent bulk glass ceramic containing Cr3+:LiGa5O8 nanoparticles was fabricated as an alternative for monocrystal to explore the possible application in fluorescence lifetime-based temperature sensing. Such glass ceramic exhibited deep-red luminescence upon the excitation of the wide wavelength range of visible light. Impressively, the Cr3+ lifetime dramatically decreased from 2.45 to 0.22 ms with the temperature increasing from 293 to 563 K, owing to the competition of radiation transitions from the thermally coupled 2E and 4T2 excited states. A two-level kinetic model was adopted to interpret this temperature-dependent luminescence of Cr3+, which gave a highest temperature sensitivity of 1.15%  K(-1).

Achieving efficient Tb3+ dual-mode luminescence via Gd-sublattice-mediated energy migration in a NaGdF4 core–shell nanoarchitecture

A strategy to realize dual-mode luminescence from identical Tb3+ is provided via Gd-sublattice-mediated energy migration and core–shell engineering techniques. By optimizing the structure of a NaGdF4:Yb/Tm@NaGdF4:Ce/Tb nanoarchitecture, both upconversion and downshifting emissions, originating from 5D4 → 7F6,5,4,3 transitions of Tb3+, are achieved through Yb3+ → Tm3+ → [Gd3+]n → Tb3+ and Ce3+ → [Gd3+]n → Tb3+ energy transfer processes, respectively.

A dual-functional upconversion core@shell nanostructure for white-light-emission and temperature sensing

A strategy to simultaneously achieve white-light-emission and temperature sensing via a 980 nm excitable upconversion core@shell nanoarchitecture design was provided. Specifically, the prepared Yb/Ho/Ce: NaGdF4@Yb/Tm: NaYF4 active-core@active-shell nanocrystals enabled the spatially confined doping of Ho3+ in the core and Tm3+ in the shell and thus greatly reduced the adverse energy transfers between them, leading to intense upconversion emissions for both Ho3+ and Tm3+ activators. Notably, introducing Ce3+ into the core resulted in the competition of radiation transitions from the Ho3+: 5S2, 5F4 green-emitting states and Ho3+: 5F5 red-emitting one, which was beneficial to tune the red to green intensity ratio and ultimately realize white-light luminescence. Temperature-dependent upconversion emission spectra of the core@shell samples evidenced the joint contribution of Ce3+ in the core and Tm3+ in the shell to improve sensitivity for temperature detection. As a consequence, the core@shell nanostructure was demonstrated to have a high temperature sensitivity (2.4% K−1) and excellent signal discriminability (3040 cm−1), being potentially applicable as an optical thermometric material.

Dual-activator luminescence of RE/TM:Y3Al5O12 (RE = Eu3+, Tb3+, Dy3+; TM = Mn4+, Cr3+) phosphors for self-referencing optical thermometry

Traditional optical temperature sensors based on the rare earth fluorescence intensity ratio of two thermally coupled energy states have intrinsic limitations such as low relative sensitivity and large detection error due to the requirement of a narrow energy gap. Herein, a strategy involving the use of rare earth and transition metal dual-emitting centers with completely different thermal-quenching behaviors has been developed to achieve high temperature sensitivity and good discrimination of signals. In particular, Eu3+/Mn4+:Y3Al5O12 with strikingly high absolute and relative sensitivities of 0.441 K−1 and 4.81% K−1 as well as a large energy gap of 2100 cm−1 was realized by taking advantage of Eu3+ luminescence as a reference signal and Mn4+ luminescence as a temperature signal. The versatility of the proposed strategy has been demonstrated by adopting other Tb3+/Mn4+, Dy3+/Mn4+, Eu3+/Cr3+ and Dy3+/Cr3+ dual-activator combinations. It is expected that this preliminary study will provide an important advance in exploring novel self-referencing optical thermometry with excellent performance.

Phase structure control and optical spectroscopy of rare-earth activated GdF3 nanocrystal embedded glass ceramics via alkaline-earth/alkali-metal doping

Hexagonal to orthorhombic phase transformation of GdF3 nanocrystals in bulk glass ceramics was achieved through alkaline-earth/alkali-metal doping and crystallization temperature controlling. Structural characterizations and spectroscopic analyses of the Eu3+ probe evidenced the incorporation of rare earth emitting-centers into the precipitated GdF3 crystals among the glass matrix. In addition, the influence of phase evolution on the upconversion luminescence of Er3+/Yb3+ co-doped glass ceramics was systematically investigated and it was evidenced that the upconversion intensity of the orthorhombic GdF3 embedded glass ceramic was two orders of magnitude higher than that of the hexagonal GdF3 containing glass ceramic. Benefiting from greatly enhanced upconversion luminescence after glass crystallization, the present glass ceramic composites were demonstrated to have promising applications in optical temperature sensors as well as tunable displays.