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 Ln³⁺ (Ln = Eu, Tb, Dy) luminescence as reference signal and Cr³⁺ emission as temperature signal was provided. Specifically, the synthesized dual-phase glass-ceramics were evidenced to enable spatially confined doping of Ln³⁺ in the hexagonal GdF₃ nanocrystals and Cr³⁺ in the cubic Ga₂O₃ nanoparticles, being beneficial to suppressing detrimental energy transfer between Ln³⁺ and Cr³⁺ and thus significantly enhancing their luminescence. As a consequence, completely different temperature-sensitive luminescence of Ln³⁺4f → 4f transition and Cr³⁺ 3d → 3d transition in the present glass-ceramic resulted in obvious variation of Cr³⁺/Ln³⁺ 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

A Bifunctional Cr/Yb/Tm:Ca₃Ga₂Ge₃O₁₂ Phosphor with Near-Infrared Long-Lasting Phosphorescence and Upconversion Luminescence

Currently, upconversion nanocrystals and long-lasting phosphorescent particles have attracted extensive research interest for their possible applications as bioimaging probes. However, there are few reports concerning the achievement of both upconversion luminescence of lanthanide ions and long-lasting phosphorescence of transition metal ions in a sole host so far. Herein, we demonstrate a novel calcium gallium germanium garnet (Ca3Ga2Ge3O12) host where lanthanide ions such as Tm3+/Yb3+ and transition metal ions such as Cr3+ can be easily incorporated through substituting the Ca2+ and Ga3+ respectively. This Cr/Yb/Tm:Ca3Ga2Ge3O12 phosphor exhibits both broadband near-infrared long-lasting phosphorescence of Cr3+ with an afterglow time of more than 7000 s and near-infrared to near-infrared upconversion luminescence of Tm3+. Impressively, it is evidenced that the addition of Yb3+/Tm3+ into Cr:Ca3Ga2Ge3O12 not only results in Tm3+ upconversion luminescence but also greatly increases Cr3+ afterglow time. Based on excitation/emission, three-dimensional thermoluminescence, and time-resolved luminescence spectra, the related long-lasting phosphorescence and upconversion luminescent mechanisms are systematically discussed as well

EuF₃/Ga₂O₃ Dual-Phase Nanostructural Glass Ceramics with Eu²⁺/Cr³⁺ Dual-Activator Luminescence for Self-Calibrated Optical Thermometry

To circumvent the requirement of small energy gap between thermally coupled levels of lanthanide probes in optical thermometry, a strategy using dual-activator fluorescence intensity ratio as temperature signal in dual-phase nanostructural glass ceramics was reported. Specifically, oxyfluoride glass with specially designed composition of SiO₂–Al₂O₃–LiF–EuF₃–Ga₂O₃–Cr₂O₃ was fabricated, and subsequently glass crystallization was used to induce homogeneous precipitation of hexagonal EuF₃ and cubic Ga₂O₃ nanocrystals among the glass matrix. Impressively, Eu²⁺ activators were produced after glass crystallization in an air atmosphere, and the Cr³⁺ emitting center was evidenced to incorporate into Ga₂O₃ crystalline lattice. As a result, temperature determination with high sensitivity of 0.8% K^–1, large energy gap of 8500 cm^–1, and superior thermal stability were realized by taking advantage of the fluorescence intensity ratio between Eu²⁺ and Cr³⁺ as detecting parameter, which exhibited a linear dependence on temperature. We believe that this preliminary investigation will provide a practical approach for developing a high-performance self-calibrated optical thermometer

Shape Control of Monodisperse CdS Nanocrystals: Hexagon and Pyramid

The wurtzite CdS nanocrystals with hexagonal or pyramidal geometries were selectively synthesized by tuning the molar ratio of Cd and S precursors in the solution system. For hexagonal nanocrystals, a 2-D or 3-D superlattice assembly could be obtained due to the narrow particle size distribution. The pyramidal CdS nanocrystals were divided into two geometries:  the hexagon-based pyramid and the triangle-based pyramid. The realization of the pyramidal geometries further extends the shape multiformity of wurtzite CdS nanocrystals, which may bring new opportunities for the development of CdS semiconductors. The room-temperature absorption spectra of CdS nanoparticles with hexagonal and pyramidal morphologies exhibited a discrepancy in peak positions, revealing the existence of a profound shape−property relationship for the CdS nanophase

Tunable Red-Green Upconversion Luminescence in Novel Transparent Glass Ceramics Containing Er: NaYF₄ Nanocrystals

To develop NaYF4 as bulk luminescence material, transparent glass ceramics containing Er3+:  NaYF4 nanocrystals were fabricated for the first time, and the influences of heat-treatment temperature and Er3+ doping level on their upconversion luminescence were investigated. With increasing heating temperature, the upconversion intensity enhanced accordingly, attributing to the incorporation of more Er3+ into the grown NaYF4. Notably, when the heating temperature reached 650 °C, the upconversion intensity augmented drastically due to the occurrence of phase transition from the cubic NaYF4 to the hexagonal one. Interestingly, for the samples heat-treated at 620 °C, when the Er3+ doping level was increased from 0.05 to 2.0 mol %, the upconversion emission was whole-range tunable from monochromatic green to approximately monochromatic red, which could be mainly attributed to the cross-relaxation between Er3+ ions. The excellent optical properties and its convenient, low-cost synthesis of the present glass ceramic imply that it is an excellent substitution material for the unobtainable bulk NaYF4 crystal, potentially applicable in many fields

Modifying the Size and Shape of Monodisperse Bifunctional Alkaline-Earth Fluoride Nanocrystals through Lanthanide Doping

In this communication, a simple route for modifying the uneven size and shape of alkaline-earth fluoride nanophases to monodisperse ultrasmall nanospheres through lanthanide doping is offered. These nanospheres are found to exhibit bifunctionality, i.e., tunable upconversion emissions as well as proper paramagnetism, making them potentially applicable in the biological field. The synthesis strategy, which involves doping of an impurity with a different valence than the cation in the nanophase, might be useful for controlling the solution growth of some technologically important nanomaterials

In Situ Crystallization Synthesis of CsPbBr₃ Perovskite Quantum Dot-Embedded Glasses with Improved Stability for Solid-State Lighting and Random Upconverted Lasing

All-inorganic cesium lead bromide CsPbBr₃ perovskite quantum dots (QDs) are emerging as potential candidates for their applications in optoelectronic devices but they suffer from poor long-term stability due to their high sensitivity to UV irradiation, heat, and especially to moisture. Although great advances in improving stability of perovskite QDs have been achieved by surface modification or encapsulation in polymer and silica, they are not sufficiently refrained from external environment due to nondense structures of these protective layers. In this work, in situ nanocrystallization strategy is developed to directly grow CsPbBr₃ QDs among a specially designed TeO₂-based glass matrix. As a result, QD-embedded glass shows typical bright green emission assigned to exciton recombination radiation and significant improvement of photon/thermal stability and water resistance due to the effective protecting role of dense structural glass. Particularly, ∼90% of emission intensity is even remained after immersing QD-embedded glass in water up to 120 h, enabling them to find promising applications in white-light-emitting device with superior color stability and low-threshold random upconverted laser under ambient air condition