Large-Area Patterning of Polyaniline Film Based on <i>in Situ</i> Self-Wrinkling and Its Reversible Doping/Dedoping Tunability

Here we report a simple one-pot yet robust approach to fabricate large-scale wrinkle patterns with reversible acid-doping/base-dedoping tunability. A novel swelling-induced self-wrinkling mechanism is responsible for the <i>in situ</i> growth of wrinkled polyaniline (PANI) film on polydimethylsiloxane (PDMS) substrate. The spontaneously formed wrinkles with controlled microstructures such as the wavelength, spatial orientation, and location have been well regulated by PANI film thickness (via polymerization time and monomer concentration) and PDMS substrate modulus as well as the boundary conditions imposed by the substrate. The results indicate that the <i>in situ</i> self-wrinkling is highly desirable for patterning PANI film over large areas with the instability-driven morphologies, even in the case of curved surfaces employed. Interestingly, taking advantage of the swelling/deswelling capability via the unique acid doping/base dedoping of PANI, we have further realized unprecedented reversible modulation between the wrinkled and dewrinkled states. The involved physics underlying the complicated <i>in situ</i> self-wrinkling and the reversible doping/dedoping tunability has been revealed

Cation Substitution Dependent Bimodal Photoluminescence in Whitlockite Structural Ca_3–<i>x</i>Sr_<i>x</i>(PO₄)₂:Eu²⁺ (0 ≤ <i>x</i> ≤ 2) Solid Solution Phosphors

Cation substitution dependent tunable bimodal photoluminescence behavior was observed in the Ca_3–<i>x</i>Sr_<i>x</i>(PO₄)₂:Eu²⁺ (0 ≤ <i>x</i> ≤ 2) solid solution phosphors. The Rietveld refinements verified the phase purity and whitlockite type crystal structure of the solid solutions. The tunable photoluminescence evolution was studied as a function of strontium content, over the composition range 0.1 ≤ <i>x</i> ≤ 2. In addition to the emission band peak at 416 nm in Ca₃(PO₄)₂:Eu²⁺, the substitution of Ca²⁺ by Sr²⁺ induced the emerging broad-band peak at 493–532 nm. A dramatic red shift of the emission peak located in the green-yellow region was observed on an increase of <i>x</i> in the samples with 0.75 ≤ <i>x</i> ≤ 2.00. The two emission bands could be related to the EuO_<i>n</i>–Ca₉ and EuO_<i>n</i>–Ca_9–<i>x</i>Sr_<i>x</i> emitting blocks, respectively. The values for the two kinds of emitting blocks in the solid solutions can be fitted well with the observed intensity evolution of the two emission peaks

Cation Substitution Dependent Bimodal Photoluminescence in Whitlockite Structural Ca_3–<i>x</i>Sr_<i>x</i>(PO₄)₂:Eu²⁺ (0 ≤ <i>x</i> ≤ 2) Solid Solution Phosphors

Cation substitution dependent tunable bimodal photoluminescence behavior was observed in the Ca_3–<i>x</i>Sr_<i>x</i>(PO₄)₂:Eu²⁺ (0 ≤ <i>x</i> ≤ 2) solid solution phosphors. The Rietveld refinements verified the phase purity and whitlockite type crystal structure of the solid solutions. The tunable photoluminescence evolution was studied as a function of strontium content, over the composition range 0.1 ≤ <i>x</i> ≤ 2. In addition to the emission band peak at 416 nm in Ca₃(PO₄)₂:Eu²⁺, the substitution of Ca²⁺ by Sr²⁺ induced the emerging broad-band peak at 493–532 nm. A dramatic red shift of the emission peak located in the green-yellow region was observed on an increase of <i>x</i> in the samples with 0.75 ≤ <i>x</i> ≤ 2.00. The two emission bands could be related to the EuO_<i>n</i>–Ca₉ and EuO_<i>n</i>–Ca_9–<i>x</i>Sr_<i>x</i> emitting blocks, respectively. The values for the two kinds of emitting blocks in the solid solutions can be fitted well with the observed intensity evolution of the two emission peaks

Cation Substitution Dependent Bimodal Photoluminescence in Whitlockite Structural Ca_3–<i>x</i>Sr_<i>x</i>(PO₄)₂:Eu²⁺ (0 ≤ <i>x</i> ≤ 2) Solid Solution Phosphors

Cation substitution dependent tunable bimodal photoluminescence behavior was observed in the Ca_3–<i>x</i>Sr_<i>x</i>(PO₄)₂:Eu²⁺ (0 ≤ <i>x</i> ≤ 2) solid solution phosphors. The Rietveld refinements verified the phase purity and whitlockite type crystal structure of the solid solutions. The tunable photoluminescence evolution was studied as a function of strontium content, over the composition range 0.1 ≤ <i>x</i> ≤ 2. In addition to the emission band peak at 416 nm in Ca₃(PO₄)₂:Eu²⁺, the substitution of Ca²⁺ by Sr²⁺ induced the emerging broad-band peak at 493–532 nm. A dramatic red shift of the emission peak located in the green-yellow region was observed on an increase of <i>x</i> in the samples with 0.75 ≤ <i>x</i> ≤ 2.00. The two emission bands could be related to the EuO_<i>n</i>–Ca₉ and EuO_<i>n</i>–Ca_9–<i>x</i>Sr_<i>x</i> emitting blocks, respectively. The values for the two kinds of emitting blocks in the solid solutions can be fitted well with the observed intensity evolution of the two emission peaks

Discovery of New Solid Solution Phosphors via Cation Substitution-Dependent Phase Transition in M₃(PO₄)₂:Eu²⁺ (M = Ca/Sr/Ba) Quasi-Binary Sets

The cation substitution-dependent phase transition was used as a strategy to discover new solid solution phosphors and to efficiently tune the luminescence property of divalent europium (Eu²⁺) in the M₃(PO₄)₂:Eu²⁺ (M = Ca/Sr/Ba) quasi-binary sets. Several new phosphors including the greenish-white SrCa₂(PO₄)₂:Eu²⁺, the yellow Sr₂Ca­(PO₄)₂:Eu²⁺, and the cyan Ba₂Ca­(PO₄)₂:Eu²⁺ were reported, and the drastic red shift of the emission toward the phase transition point was discussed. Different behavior of luminescence evolution in response to structural variation was verified among the three M₃(PO₄)₂:Eu²⁺ joins. Sr₃(PO₄)₂ and Ba₃(PO₄)₂ form a continuous isostructural solid solution set in which Eu²⁺ exhibits a similar symmetric narrow-band blue emission centered at 416 nm, whereas Sr²⁺ substituting Ca²⁺ in Ca₃(PO₄)₂ induces a composition-dependent phase transition and the peaking emission gets red shifted to 527 nm approaching the phase transition point. In the Ca_3–<i>x</i>Ba_<i>x</i>(PO₄)₂:Eu²⁺ set, the validity of crystallochemical design of phosphor between the phase transition boundary was further verified. This cation substitution strategy may assist in developing new phosphors with controllably tuned optical properties based on the phase transition

New Yellow-Emitting Whitlockite-type Structure Sr_1.75Ca_1.25­(PO₄)₂:Eu²⁺ Phosphor for Near-UV Pumped White Light-Emitting Devices

New compound discovery is of interest in the field of inorganic solid-state chemistry. In this work, a whitlockite-type structure Sr_1.75Ca_1.25­(PO₄)₂ newly found by composition design in the Sr₃(PO₄)₂–Ca₃(PO₄)₂ join was reported. Crystal structure and luminescence properties of Sr_1.75Ca_1.25­(PO₄)₂:Eu²⁺ were investigated, and the yellow-emitting phosphor was further employed in fabricating near-ultraviolet-pumped white light-emitting diodes (w-LEDs). The structure and crystallographic site occupancy of Eu²⁺ in the host were identified via X-ray powder diffraction refinement using Rietveld method. The Sr_1.75Ca_1.25(PO₄)₂:Eu²⁺ phosphors absorb in the UV–vis spectral region of 250–430 nm and exhibit an intense asymmetric broadband emission peaking at 518 nm under λ_ex = 365 nm which is ascribed to the 5d–4f allowed transition of Eu²⁺. The luminescence properties and mechanism are also investigated as a function of Eu²⁺ concentration. A white LED device which is obtained by combining a 370 nm UV chip with commercial blue phosphor and the present yellow phosphor has been fabricated and exhibit good application properties

Red-Shifted Emission in Y₃MgSiAl₃O₁₂:Ce³⁺ Garnet Phosphor for Blue Light-Pumped White Light-Emitting Diodes

It is highly desirable to red shift the emission of Y₃Al₅O₁₂:Ce³⁺ phosphor to obtain a warmer correlated color temperature (CCT) in applications for blue-light pumped white-light emitting diodes (w-LEDs) with high color rendering index (CRI). In this paper, we report the red-shifted emission of Y₃MgSiAl₃O₁₂:Ce³⁺ garnet phosphor for w-LEDs through a chemical unit cosubstituting in a solid solution design strategy. The fabrication temperature of the Y₃MgSiAl₃O₁₂:Ce³⁺ powder was optimized at 1600 °C, and its structure, photoluminescence property, micromorphology, decay curve, quantum yield, as well as the thermal stability of the samples are investigated in detail. The as-prepared Y₃MgSiAl₃O₁₂:Ce³⁺ phosphors display a broad excitation band ranging from 300 to 520 nm (centered at 450 nm) and present an intense Ce³⁺ 5d–4f emission band in the yellow light region (λ_em = 564 nm, obviously red-shifted away from Y₃Al₅O₁₂:Ce³⁺). This can be explained by the increase of the crystal-field splitting in the Ce³⁺ 5d levels owing to the chemical unit cosubstitution of Al³⁺(I) and Al³⁺(II) ions by Mg²⁺ and Si⁴⁺ ions. The quantum yield of the Y_2.92MgSiAl₃O₁₂:0.08Ce³⁺ phosphor is measured as 61.8%. Further investigation on a lamp packaged w-LEDs combining Y_2.92MgSiAl₃O₁₂:0.08Ce³⁺ phosphors on a blue InGaN chip shows it to exhibits a lower CCT and higher CRI compared to those of the commercial Y₃Al₅O₁₂:Ce³⁺-based devices, indicating their appealing strengths for potential applications in w-LEDs

Simple and Versatile Strategy to Prevent Surface Wrinkling by Visible Light Irradiation

A stiff film bonded to a compliant substrate is susceptible to surface wrinkling when it is subjected to in-plane compression. Prevention of surface wrinkling is essential in many cases to maintain the integrity and functionality of this kind of system. Here we report a simple versatile technique to restrain surface wrinkling of an amorphous poly­(<i>p</i>-aminoazobenzene) (PAAB) film by visible light irradiation. The key idea is to use the combined effects of photosoftening of the PAAB film and the stress release induced by the reversible photoisomerization. The main finding given by experiments and dimensional analysis is that the elastic modulus <i>E</i>_f of the film is well modulated by the ratio of light intensity and the release rate, i.e., <i>I</i>/<i>V</i>. Furthermore, the explicit solution describing the correlation of <i>I</i>/<i>V</i> with <i>E</i>_f is derived for the first time. The difference between the calculated critical wrinkling strain ε_c,t based on <i>E</i>_f and the experimentally measured value ε_c enables us to quantitatively evaluate the release amount of the compressive stress in the film. These key solutions provide a simple strategy to prevent the undesired surface wrinkling. Additionally, they allow us to propose a wrinkling-based technique to investigate photoinduced changes in the mechanical properties of azo-containing materials

Simple and Versatile Strategy to Prevent Surface Wrinkling by Visible Light Irradiation

A stiff film bonded to a compliant substrate is susceptible to surface wrinkling when it is subjected to in-plane compression. Prevention of surface wrinkling is essential in many cases to maintain the integrity and functionality of this kind of system. Here we report a simple versatile technique to restrain surface wrinkling of an amorphous poly­(<i>p</i>-aminoazobenzene) (PAAB) film by visible light irradiation. The key idea is to use the combined effects of photosoftening of the PAAB film and the stress release induced by the reversible photoisomerization. The main finding given by experiments and dimensional analysis is that the elastic modulus <i>E</i>_f of the film is well modulated by the ratio of light intensity and the release rate, i.e., <i>I</i>/<i>V</i>. Furthermore, the explicit solution describing the correlation of <i>I</i>/<i>V</i> with <i>E</i>_f is derived for the first time. The difference between the calculated critical wrinkling strain ε_c,t based on <i>E</i>_f and the experimentally measured value ε_c enables us to quantitatively evaluate the release amount of the compressive stress in the film. These key solutions provide a simple strategy to prevent the undesired surface wrinkling. Additionally, they allow us to propose a wrinkling-based technique to investigate photoinduced changes in the mechanical properties of azo-containing materials

Simple and Versatile Strategy to Prevent Surface Wrinkling by Visible Light Irradiation

A stiff film bonded to a compliant substrate is susceptible to surface wrinkling when it is subjected to in-plane compression. Prevention of surface wrinkling is essential in many cases to maintain the integrity and functionality of this kind of system. Here we report a simple versatile technique to restrain surface wrinkling of an amorphous poly­(<i>p</i>-aminoazobenzene) (PAAB) film by visible light irradiation. The key idea is to use the combined effects of photosoftening of the PAAB film and the stress release induced by the reversible photoisomerization. The main finding given by experiments and dimensional analysis is that the elastic modulus <i>E</i>_f of the film is well modulated by the ratio of light intensity and the release rate, i.e., <i>I</i>/<i>V</i>. Furthermore, the explicit solution describing the correlation of <i>I</i>/<i>V</i> with <i>E</i>_f is derived for the first time. The difference between the calculated critical wrinkling strain ε_c,t based on <i>E</i>_f and the experimentally measured value ε_c enables us to quantitatively evaluate the release amount of the compressive stress in the film. These key solutions provide a simple strategy to prevent the undesired surface wrinkling. Additionally, they allow us to propose a wrinkling-based technique to investigate photoinduced changes in the mechanical properties of azo-containing materials