ABSTRACT
A 0.25% iron (Fe3+)-doped LiGaO2 phosphor was synthesized by a high-temperature solid-state reaction method. The phosphor was characterized utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM), high-pressure photoluminescence, and photoluminescence decay measurement techniques using diamond anvil cells (DACs). The powder X-ray analysis shows that the phosphor is a ß polymorph of LiGaO2 with an orthorhombic crystallographic structure at room temperature. The SEM result also confirms the presence of well-dispersed micro-rod-like structures throughout the sample. The photoluminescence studies in the near-infrared (NIR) range were performed at ambient, low-temperature, and high-pressure conditions. The synthesized phosphor exhibits a photoluminescence band around 746 nm related to the 4T1 â 6A1 transition with a 28% quantum efficiency at ambient conditions, which shifts toward longer wavelengths with the increase of pressure. The excitation spectra of Fe3+ are very well fitted with the Tanabe-Sugano crystal-field theory. The phosphor luminescence decays with a millisecond lifetime. The high-pressure application transforms the ß polymorph of LiGaO2 into a trigonal α structure at the pressure of about 3 GPa. Further increase of pressure quenches the Fe3+ luminescence due to the amorphization process of the material. The prepared phosphor exhibits also mechanoluminescence properties in the NIR spectral region.
ABSTRACT
α-SrSi2O2N2 is one of the recently studied oxonitridosilicates applicable in optoelectronics, in particular in white LEDs. Its elastic properties remain unknown. A survey of literature shows that, up to now, nine oxonitridosilicate materials have been identified. For most of these compounds, doped with rare earths and manganese, a luminescence has been reported at a wavelength characteristic for the given material; all together cover a broad spectral range. The present study focuses on the elastic properties of one of these oxonitridosilicates, the Eu-doped triclinic α-SrSi2O2N2. High-pressure powder diffraction experiments are used in order to experimentally determine, for the first time, the equation of state of this compound. The in situ experiment was performed for pressures ranging up to 9.65 GPa, for Eu-doped α-SrSi2O2N2 sample mounted in a diamond anvil cell ascertaining the hydrostatic compression conditions. The obtained experimental variation of volume of the triclinic unit cell of α-SrSi2O2N2:Eu with rising pressure served for determination of the Birch-Murnaghan equation of state. The determined above quoted bulk modulus is 103(5) GPa, its first derivative is 4.5(1.1). The above quoted bulk modulus value is found to be comparable to that of earlier reported oxynitrides of different composition.
ABSTRACT
Endowing a single material with various types of luminescence, that is, exhibiting a simultaneous optical response to different stimuli, is vital in various fields. A photoluminescence (PL)- and mechanoluminescence (ML)-based multifunctional sensing platform is built by combining heterojunctioned ZnS/CaZnOS:Mn2+ mechano-photonic materials using a 3D-printing technique and fiber spinning. ML-active particles are embedded in micrometer-sized cellulose fibers for flexible optical devices capable of emitting light driven by mechanical force. Individually modified 3D-printed hard units that exhibit intense ML in response to mechanical deformation, such as impact and friction, are also fabricated. Importantly, they also allow low-pressure sensing up to ≈100 bar, a range previously inaccessible by any other optical sensing technique. Moreover, the developed optical manometer based on the PL of the materials demonstrates a superior high-pressure sensitivity of ≈6.20 nm GPa-1 . Using this sensing platform, four modes of temperature detection can be achieved: excitation-band spectral shifts, emission-band spectral shifts, bandwidth broadening, and lifetime shortening. This work supports the possibility of mass production of ML-active mechanical and optoelectronic parts integrated with scientific and industrial tools and apparatus.