Broadband Solar-blind Ultraviolet Spectroscopy Modulation And Its Application Based On Energy Transfer Of Rare Earth Ions

The strong absorption of the atmosphere makes ultraviolet(UV)light with a wavelength of200 to 280 nm belong to the blind zone in the Earth,which is known as solar-blind UV window because it cannot reach the Earth's surface.Due to the low natural background of the solar-blind spectral region,the detector acting on this window has the advantages that other detection equipments can not match,such as high signal-to-noise ratio,high accuracy and work no matter what the weather or time.Benefitted from this distinctive advantage,solar-blind photodetectors are expected to be applied in missile warning and tracking,UV communications,medical diagnosis,flame detection and other fields.Solar-blind UV photodetectors based on quantum dot materials and wide bandgap(WBG)semiconductors are appearing in an endless stream in the latest century.However,the WBG semiconductor usually requires complex preparation process and high technical requirements.Most of the materials used in quantum dot based detectors contain toxic elements such as lead,which will cause environmental pollution and other problems in the process of actual production and application.In addition,most of the existing solar-blind UV detection techniques can only achieve narrow range detection.Therefore,it is of great significance for the rapid development of photoelectric technology to explore a solar-blind UV detector with simple preparation method,environmental friendliness and wide response range.Down-conversion(DC)luminescent materials doped with rare earth(RE),due to its simple synthesis method,environmentally friendly raw materials and special quantum tailoring properties,are expected to be used as spectral converters to achieve spectral modulation of solar-blind UV light.That is,they can convert solar-blind UV light into visible light that can be responded by ordinary semiconductors.In addition,the DC luminescent materials have broadband solar-blind UV light absorption spectrum,so it is expected to realize broadband solar-blind UV detection by combining with ordinary semiconductor.With that in mind,the main research contents and conclusions of this paper are as follows:1.Gd₂O₃:x%Eu³⁺(x=0?1?3?5?7?10)phosphors were synthesized by hydrothermal method.XRD patterns showed that all the samples had cubic phase structure and good crystallinity.By observing the UV-visible(UV-Vis)absorption spectra,it was found that the samples had a wide band absorption in the solar-blind UV region,and the fluorescence spectra showed a sharp emission peak near the visible light at 610 nm.These results show that the Gd₂O₃:Eu³⁺phosphors with excellent spectral modulation characteristics.Subsequently,the Gd₂O₃:Eu³⁺phosphor was mixed with PMMA to form a transparent organic-inorganic composite film,which was used as a spectral converter to cover the surface of silicon based photosensitive resistance(Si-BPR).The current-voltage(I-V)characteristic curve of Si-BPR was observed under excitation of solar-blind UV light with different wavelength.An obvious photocurrent signal was detected when the wavelength of the excitation source was greater than 234 nm.The photoelectric response of detecting equipment under pulse excitation shows that the photovoltage value increases/attenuates rapidly when the light source is turned on/off,and then tends to be stable.In multiple test periods,the photovoltage value does not attenuate.These results prove that the composite device can realize the high efficiency,sensitivity and stability detection of broadband solar-blind UV light.2.The Y₂O₃:x%Eu³⁺(x=5,10,12,15,20)phosphors were synthesized by hydrothermal method.The optical properties show that all the samples have a wide band absorption spectrum in the solar-blind UV region,and their fluorescence emission is attributed to the characteristic emission spectrum of Eu³⁺,which is attributed to the ⁵D₀-⁷F_J(J=0,1,2,3)level state transitions.Y₂O₃:15%Eu³⁺-PMMA composite film is transparent when it's exposed to natural light.However,the composite film emits bright red light just like a red sun under the excitation of UV light,which proves that the composite film can effectively modulate UV radiation into visible light.Similarly,when the Y₂O₃:15%Eu³⁺-PMMA film is composite with ordinary semiconductor,an obvious photoelectric response is observed under the excitation of broadband solar-blind UV light.And the detection equipment based on Y₂O₃:Eu³⁺phosphor also has high sensitivity and good stability and repeatability.The solar-blind UV detection scheme proposed in this paper is universal and suitable for a variety of DC luminescent materials doped with RE.3.A series of Y₂O₃:x%Eu³⁺+y%M⁺(x,y=0?5?7?10?12?15;M=Li?Na?K)phosphors were synthesized by low temperature combustion.And the effects of alkali ions on the structure and morphology,optical and photoelectric properties of the DC luminescence layer were investigated in this paper.XRD and SEM images show that the introduction of alkali metal ions(Li⁺?Na⁺?K⁺)did not change the crystal structure of the phosphors,but improves the crystallinity of the samples and the size of the phosphors nanoparticles.The optical properties of the samples showed that the introduction of alkali metal ions did not change the characteristics of UV-Vis absorption and emission spectra.However,the intensity of the emission peak of the sample is significantly enhanced,which is attributed to the change of the symmetry of the crystal field near Eu³⁺ions by alkali metal ions.In addition,it was found that the solar-blind UV detection device has high sensitivity,good reproducibility and excellent stability before and after the introduction of alkali metal ion Li⁺.The difference is that the introduction of Li⁺ions makes the response signal of the photoelectric detection equipment increase to about 2 times compared with the original,which proves that the introduction of alkali metal ions realizes the enhancement of the solar-blind UV detection based on RE luminescent materials.