Research of Fluorescent Properties of a New Type of Phosphor with Mn2+-Doped Ca2SiO4

Synthesis, Structure and Luminescence Properties of Mn-doped MgAl2O4 Red-Emitting Phosphors with Varying Sintering Temperature

Oxide matrix red-emitting phosphors are deemed as excellent color converters for white light emitting diodes (WLEDs) and laser diodes (LDs). Manganese-doped MgAl2O4 powder was synthesized by a solid-state reaction method at different sintering temperatures. Microstructure shows that grain size is mainly in the range of 0.2-5 μm, and grain agglomeration occurs with increased sintering temperature. XPS analysis indicates that the doped Mn ion exhibits a valence state of + 4 within the MgAl2O4 matrix. The diffraction peak of the phosphors is shifted by the sintering temperature, which affects lattice constant. Upon excitation by 300 nm ultraviolet light, the samples emit asymmetric broadband red light within the range of 620-720 nm, attributed to Mn4+ ion's transition from 2Eg to 4A2g states. With the increasing temperature, the main emission peak shifts from 677 nm to 650 nm, ascribed to the change in energy level (2Eg) resulting from the reduction of Al2O3 phase. Crystal field theory confirmed that Mn4+ ions are within a strong crystal field environment created by MgAl2O4 matrix. By affecting particle size and crystallinity, the sintering temperature influences the fluorescence lifetime of the Mn4+ ion. Notably, these red-emitting phosphors exhibits remarkable thermal stability as their emission intensity remains approximately at 58% of initial intensity even at elevated temperature (435 K). Consequently, Mn4+: MgAl2O4 red-emitting phosphors with high thermal stability render them promising candidates for WLED applications.

Luminescence Dynamics of BaAl2O4:Eu2+ Phosphor

We studied steady-state and time-resolved photoluminescence of Eu doped BaAl2O4 phosphor. The undoped BaAl2O4 sample shows a dominant blue emission band at ~ 428 nm and two secondary maxima at ~ 405 and 456 nm due to F-centre and aggregate defects such as F2 -centre. The samples after doping of Eu at 1-5% show additional emission bands at ~ 485 and 518 nm due to Eu2+ centre and a red emission band at ~ 657 nm is attributed to Eu3+ centre. The sample doped with 2% of Eu shows anomalous emission having the dominant peak at ~ 494 nm. The average luminescence lifetime of the emission band at ~ 428 nm in the undoped sample was estimated to be (3.29 ± 0.91) ns. The average luminescence lifetime of this emission band after doping of Eu was found to increase by 102 orders of magnitude. The intensity of the 428 nm blue emission band was found to quench after doping of Eu beyond 3%. The concentration quenching effect was attributed to dipole-quadrupole interaction. Further, a non-radiative fluorescence energy transfer mechanism from an extrinsic Eu2+ centre to an intrinsic F-centre is proposed to describe the luminescence dynamics of the samples.

Recent Advances in Light-Conversion Phosphors for Plant Growth and Strategies for the Modulation of Photoluminescence Properties

The advent of greenhouses greatly promoted the development of modern agriculture, which freed plants from regional and seasonal constraints. In plant growth, light plays a key role in plant photosynthesis. The photosynthesis of plants can selectively absorb light, and different light wavelengths result in different plant growth reactions. Currently, light-conversion films and plant-growth LEDs have become two effective ways to improve the efficiency of plant photosynthesis, among which phosphors are the most critical materials. This review begins with a brief introduction of the effects of light on plant growth and the various techniques for promoting plant growth. Next, we review the up-to-date development of phosphors for plant growth and discussed the luminescence centers commonly used in blue, red and far-red phosphors, as well as their photophysical properties. Then, we summarize the advantages of red and blue composite phosphors and their designing strategies. Finally, we describe several strategies for regulating the spectral position of phosphors, broadening the emission spectrum, and improving quantum efficiency and thermal stability. This review may offer a good reference for researchers improving phosphors to become more suitable for plant growth.

Spatially Resolved Temperature Distribution in a Rare-Earth-Doped Transparent Glass-Ceramic

Knowing the temperature distribution within the conducting walls of various multilayer-type materials is crucial for a better understanding of heat-transfer processes. This applies to many engineering fields, good examples being photovoltaics and microelectronics. In this work we present a novel fluorescence technique that makes possible the non-invasive imaging of local temperature distributions within a transparent, temperature-sensitive, co-doped Er:GPF1Yb0.5Er glass-ceramic with micrometer spatial resolution. The thermal imaging was performed with a high-resolution fluorescence microscopy system, measuring different focal planes along the z-axis. This ultimately enabled a precise axial reconstruction of the temperature distribution across a 500-µm-thick glass-ceramic sample. The experimental measurements showed good agreement with computer-modeled heat simulations and suggest that the technique could be adopted for the spatial analyses of local thermal processes within optically transparent materials. For instance, the technique could be used to measure the temperature distribution of intermediate, transparent layers of novel ultra-high-efficiency solar cells at the micron and sub-micron levels.

Transition Metals (Cr3+) and Lanthanides (Eu3+) in Inorganic Glasses with Extremely Different Glass-Formers B2O3 and GeO2

Glasses containing two different network-forming components and doped with optically active ions exhibit interesting properties. In this work, glass systems based on germanium dioxide and boron trioxide singly doped with lanthanides (Eu³⁺) and transition metals (Cr³⁺) ions are research subjects. Optical spectroscopy was the major research tool used to record excitation and emission spectra in a wide spectral range for studied systems. The emitted radiation of glasses doped with Cr³⁺ ions is dominated by broadband luminescence centered at 770 nm and 1050 nm (⁴T₂ → ⁴A₂). Interestingly, the increase of concentration of one of the oxides contributed to the detectable changes of the R-line (²E → ⁴A₂) of Cr³⁺ ions. Moreover, EPR spectroscopy confirmed the paramagnetic properties of the obtained glasses. The influence of molar ratio GeO₂:B₂O₃ on spectroscopic properties for Eu³⁺ ions is discussed. The intensity of luminescence bands due to transitions of trivalent europium ions as well as the ratio R/O decrease with the increase of B₂O₃. On the other hand, the increase in concentration B₂O₃ influences the increasing tendency of luminescence lifetimes for the ⁵D₀ state of Eu³⁺ ions. The results will contribute to a better understanding of the role of the glass host and thus the prospects for new optical materials.