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Highly efficient transparent nanophosphor films for tunable white light-emitting layered coatings
摘要： Bright luminescence in rare-earth (RE) nanocrystals, so-called nanophosphors, is generally achieved by choosing a host that enable the effective excitation of the RE activator through charge or energy transfer. Although tungstate, molybdate or vanadate compounds provide the aforementioned transfer, a comparative analysis of the efficiency of such emitters remains elusive. Herein we perform a combined structural and optical analysis, which reveals that the tetragonal GdVO4 matrix gives rise to the highest efficiency among the different transparent nanophosphor films compared. Then we demonstrate that by sequential stacking of optical quality layers made of Eu3+ and Dy3+ doped nanocrystals, it is possible to attain highly transparent white light emitting coatings of tunable shade with photoluminescence quantum yields above 35%. Layering provides precise dynamic tuning of the chromaticity based on the photoexcitation wavelength dependence of the emission of the nanophosphor ensemble without altering the chemical composition of the emitters or degrading their efficiency. Total extinction of incoming radiation along with the high quantum yields achieved make these thin layered phosphors one of the most efficient transparent white converter coatings ever developed.
关键词： rare-earth nanocrystals,transparent coatings,nanophosphors,phosphor materials,white-light emission
更新于2025-11-14 15:23:50
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Analytical and Monte Carlo comparisons on the optical transport mechanisms of powder phosphors
摘要： In indirect medical imaging systems, the optical transfer properties of powder phosphor materials are affected by the intrinsic mechanisms of light extinction. Light extinction (absorption and scattering) can be described either through theoretical models or with Monte Carlo simulation techniques. The purpose of the present paper is to compare both methodologies and assess the association of their optical parameters by examining either the structural (e.g., particle size) or the optical (e.g., light wavelength) intrinsic properties of the phosphor. Comparisons were carried out for the widely used host Gd2O2S for granular phosphors. The parameters considered in Monte Carlo simulation were: (i) a phosphor layer composed of grains with diameter 4–12 μm, (ii) the light wavelength (420 nm, 545 nm and 610 nm), (iii) the refractive index of the phosphor (real part: 2.3, imaginary part: 10?6 and 10?5), (iv) the packing density 50%. The results were compared with the Swank analytical model, based in Boltzman diffusion equation, by considering three cases for optical coefficients determination with the help of which the Luminescence Efficiency (LE) and the Modulation Transfer Function (MTF) of the phosphor could be predicted. It was found that Swank's model seems more appropriate for estimating the MTF values, presenting a deviation less than 5% in all the frequency range. for: wavelength 420 nm, considering (i) grain size 4 μm and thicknesses above 250 μm, (ii) grain size 12 μm and thicknesses above 300 μm, (b) wavelength 545 nm, grain size 8 μm and thicknesses above 160 μm, and (c) wavelength 610 nm, considering (i) grain size 4 μm and thicknesses above 200 μm, (ii) grain size 8 μm and thicknesses above 120 μm and (iii) grain size 12 μm and thicknesses above 80 μm.
关键词： Optical diffusion,X-ray detectors,Phosphor materials
更新于2025-09-19 17:15:36
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Calcination effect to the physical and optical properties of Zn <sub/>2</sub> SiO <sub/>4</sub> composite prepared by impregnation of ZnO on SiO <sub/>2</sub> amorphous nanoparticles
摘要： In this study, Zn2SiO4 composite-based ceramic was synthesised using amorphous SiO2 nanoparticles as a silicon source. The amorphous SiO2 nanoparticles which obtained from a simple precipitation process were mixed with aqueous zinc nitrate. Amorphous SiO2 nanoparticles were encapsulated by the zinc source in aqueous solution, dried, and subjected to calcination. The underwent calcination showed the changing of phases, morphology, and size with increased temperatures. During calcination, ZnO phase appeared at the beginning of heating temperature and Zn2SiO4 phase started to emerge at 800 °C onwards, as shown by XRD patterns. The optical band gap analysis of Zn2SiO4 composite was determined to be within the range of 3.12 to 3.19 eV. The diffusion of zinc ions into SiO2 nanoparticles with high surface area also reduced the phase formation temperature for Zn2SiO4, compared to a conventional solid state method. This optical characteristic is expected to be a potential candidate for phosphor materials in opto-electronic devices application.
关键词： optical properties,Zn2SiO4 composite,amorphous SiO2 nanoparticles,phosphor materials,calcination
更新于2025-09-10 09:29:36