AQUEOUS SYNTHESIS OF LUMINESCENT SEMICONDUCTORS FOR OPTO-ELECTRONIC APPLICATIONS

Author

• Saurabh Singh, University of KentuckyFollow

Author ORCID Identifier

http://orcid.org/0009-0001-9443-9406

Date Available

6-4-2026

Year of Publication

2026

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Engineering

Department/School/Program

Materials Science and Engineering

Faculty

Fuqian Yang

Faculty

Matthew Beck

Abstract

The advancement of opto-electronic and scintillation technologies relies heavily on developing low-temperature, eco-friendly, and scalable synthesis routes for high performance luminescent halide-based semiconductor materials. However, traditional synthesis methods for halide-based semiconductors, including hot-injection, solvothermal, solid-state reactions, Ligand-Assisted Reprecipitation (LARP), microwave-assisted synthesis, and thin film deposition techniques (spin coating, physical vapor deposition (PVD), chemical vapor deposition (CVD), etc.), often demand toxic organic/inorganic solvents, elevated processing temperatures, and high vacuum/inert environments. Such constraints limit their scalability, raise environmental concerns, and impede their commercial-level device integration. This research overcomes these long-standing challenges by employing water as a powerful crystallization-directing, and environmentally benign medium for the synthesis of continuous halide-based semiconductor thin films, spanning the whole visible spectrum via red, green and blue emitters. First, a low-temperature (~50 °C), water-based synthesis route is developed for the first time to produce deep-blue-emitting Eu²⁺-activated CsCl thin films, exhibiting narrow photoluminescence (PL) emission at ~442 nm (FWHM ~29.4 nm), high photoluminescence quantum yield (PLQY) of ~81.4%, and exceptional thermal stability (>125°C). The as-synthesized CsCl: Eu²⁺ films demonstrated stable Eu²⁺ luminescent centers within the host CsCl lattice, confirmed by first- principles calculations and comprehensive experimental characterization. The films also displayed negative photoconductivity (NPC) under UV irradiation, revealing previously unreported defect mediated charge-transport behavior in water-derived alkali-halide systems. Further, these films demonstrated wide color-gamut coverage (~132.81% of NTSC 1953 and ~187.51% of sRGB color standards) when integrated as blue convertors in white-emitting LCD backlight units, highlighting their superior performance compared to standard blue phosphors. Second, an interface-directed biphasic water-octadecene (ODE) strategy is introduced for the first time to synthesize size- and phase-optimized CsPbBr₃ green emitting perovskite particles at room temperature. By tuning the polarity contrast and precursor distribution across the water-ODE interface, this synthesis technique modulates the nucleation and growth kinetics along with phase selectivity, yielding both large (~0.5 μm) phase-pure CsPbBr₃ particles and smaller (~0.1 μm) mixed-phase CsPbBr₃/Cs₄PbBr₆ particles. These as-synthesized perovskite structures exhibited bright green emission (~524-534 nm), enhanced ambient stability, and wide color-gamut coverage (~123% of NTSC 1953 and ~87% of sRGB color standards) when incorporated into white-emitting LCD backlight architectures. Third, a fully aqueous, surfactant-free synthesis method is demonstrated for fabricating Pb-free continuous red-emitting CsMnBr₃ thin films at low temperatures of ~50 °C. Slow thermal evaporation of aqueous solutions containing CsBr and MnBr₂ salts, leads to formation of continuous films exhibiting strong broadband (FWHM~75 nm) red PL emission at ~644 nm (associated with Mn²⁺ octahedral units) and ultra-wide color gamut coverage (~132% of NTSC 1953 and ~186% of sRGB color standards) when integrated as red emitters in white-emitting LCD backlight structures. Further, the as-fabricated red emitting CsMnBr₃ films also displayed negative photoconductivity (NPC) under UV illuminations, analogous to the NPC behavior depicted by deep-blue emitting CsCl: Eu²⁺ thin films synthesized via water, highlighting a broader class of water-mediated charge transport mechanisms in halide semiconductor materials. Overall, these three material systems, namely deep-blue emitting CsCl: Eu²⁺ halides, green emitting CsPbBr₃ perovskites, and red-emitting Pb-free CsMnBr₃ perovskites, collectively establish water as a versatile, environmentally benign, and scalable processing medium for fabricating high-quality luminescent semiconductors at low temperatures. This work not only addresses critical sustainability and scalability issues in traditional halide material syntheses but also unfolds new mechanistic insights into water-mediated crystallization, dopant activation, defect formation, and interfacial reaction pathways. The current findings open-up promising new avenues for green and scalable synthesis of halide-based materials for next-generation optoelectronics.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2026.307

Archival?

Archival

Funding Information

This research was supported by the National Science Foundation through the CBET-2018411 monitored by Dr. Nora F Savage.

Recommended Citation

Singh, Saurabh, "AQUEOUS SYNTHESIS OF LUMINESCENT SEMICONDUCTORS FOR OPTO-ELECTRONIC APPLICATIONS" (2026). Theses and Dissertations--Chemical and Materials Engineering. 192.
https://uknowledge.uky.edu/cme_etds/192