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Title: Coupling between the properties of smart materials and light emission
Authors: Chen, Li
Degree: Ph.D.
Issue Date: 2017
Abstract: Luminescent materials and devices have drawn much attention due to their widely applications in solid-state lighting, light-emitting diodes (LEDs), architectural decoration, digital displays, bio-imagines, optical sensors and lasers. On the other side, smart materials are designed materials which are capable of responding to external stimuli, such as stress, electric or magnetic field, and so on. Herein, the coupling of smart materials and luminescence phenomenon has opened a new path to study luminescence emission and manipulate the spectral properties, and their potential has been developed from basic electronics and optoelectronics to a wide range of applications. In this thesis, firstly, a type of flexible phosphor composite has been fabricated by mixing metal ion-doped ZnS into Poly(dimethylsiloxane) (PDMS) matrix. By stimulating with a uniaxial strain of stretch and release, white and green light emission can be observed from the flexible phosphor composite. In addition, a kind of piezo-photonic luminescent device has also been fabricated via integrating the polymer phosphor layer on the top of piezoelectric actuator of Pb(Mg₁/₃Nb₂/₃)O₃-xPbTiO₃ (PMN-PT). Light emission from this hybrid device is ascribed to the non-central symmetric crystal structure of wurtzite-type ZnS material, which inherently produces piezoelectric effect under strain. Energy transitions of the observed white light emissions from the phosphor composites and device may originate from the donor acceptor pairs recombination between AlZn-CuZn, as well as the radiation transition between ⁴ T₁ and ⁶A₁ of Mn²⁺ ion.
On the other hand, significant tuning photoluminescence (PL) of smart phosphor materials has attracted widespread interest in various research fields, such as optical sensing and information storage. In contrast to traditional chemical approach, we present in-situ and real-time modulation of two kinds of smart phosphor materials in the form of piezoelectric strain and magnetostrictive stress, respectively. By integrating N,N-diphenyl-4-(1,2,2-triphenylvinyl)aniline (DPA-TPE) thin film with PMN-PT substrate or Fe-Co-Ni magnetostrictive composite respectively, the PL intensity of DPA-TPE thin film decreased linearly with the external applied electric or magnetic field. On the contrary, the new emerging organic-inorganic halide perovskite (CH₃NH₃PbI₃) shows a PL intensity enhancement during the application of biaxial piezoelectric strain provided by PMN-PT substrate. The reason may be that the biaxial strain has reduced the surface defects of the perovskite thin film. In conclusion, we have investigated different mechanical stresses to stimuli light emission from flexible phosphors composite and modulate the PL emission intensity from two types of smart phosphor materials. These findings will aid further research of luminescent materials and show promising application in optoelectronic devices and energy harvesting with various type of mechanical stresses.
Subjects: Hong Kong Polytechnic University -- Dissertations
Smart materials
Smart structures
Pages: xxvi, 134 pages : color illustrations
Appears in Collections:Thesis

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