| Environmental protection and energy conservation have become contemporary research hotspots.Light-emitting diodes(LEDs)are considered fourth-generation lighting sources with the advantages of environmental protection,high efficiency,and long life compared with the traditional incandescent lamp.Commercially available white LEDs(w-LEDs)combine a blue chip with a yellow emitting phosphor to obtain white light.However,due to a lack of a red component in the practical application of this combination design,the obtained w-LEDs suffer limitations of undesirable color-correlated temperature and low color-rendering index.Presently,the overwhelming majority of commercial red phosphors are developed with Eu3+-and Sm3+-activated oxynitride and nitride,which have outstanding red luminescence properties.However,these phosphors require harsh synthesis conditions and expensive raw materials.In recent years,Mn4+-activated phosphor has become a potential activator for red-emitting phosphors due to its attractive price,simple preparation processes,and good luminescent property.Mn4+-doped oxide phosphors have become potential red phosphors for plant growth LED because of their wide emission peak and large wavelength.In this article,a serious of Mn4+-activated phosphors are synthesized using a high-temperature solid-state reaction method in air.X ray diffraction(XRD),X-Ray Photoelectron Spectroscopy(XPS),scanning electron microscope(SEM),UV-vis absorption spectra(UV-vis),photoluminescence excitation(PLE)spectra,emission spectra(PL)spectra,Decay times,and Temperature-dependent PL spectra are used to investigate the properties of the samples.And use a large number of theoretical calculations to further explore the mechanism of concentration quenching of samples.The main research content is as follows:(1)A series of novel Ba,LaSb06(BLS):xMn4+ red-emitting phosphors are synthesized by high-temperature solid-state method.Analyses of XRD and crystal structure confirm that Mn4+ occupies the location of Sb5+ in BLS lattice.The samples are efficiently excited from 250 nm to 500 nm,which matches well with the wavelengths of UV chips for light-emitting diodes(LEDs).The photoluminescence spectra present a strong emission peak at 678 nm due to 2Eg?4A2 spin forbidden transition in Mnin ions.The decay times decrease from 0.141 ms to 0.071 ms with increasing Mn4+ concentration from x=0.03%to 0.2%because of concentration quenching.The values of decay times are within microsecond range,indicating the luminescence to be due to the forbidden transition in the intra-d-shell Mn4+ ions.The activation energy(Ea)is calculated to be?0.359 eV,confirming a good thermal stability.Quantum efficiencies of the sample are determined to be 20.2%,which is greater than that of some commercial phosphors.And the parameters of the as-fabricated LED prove BLS:Mn4+ phosphor as a potential red-emitting phosphor for W-LEDs.(2)A novel red-emitting BaLaZnTaO6:Mn4+ phosphor is synthesized by a solid-state reaction.The XRD of the as-prepared samples well match the monoclinic phase of BaLaZnTa06 without any other impurity phase.The phosphor can be excited at 350 nm,which well matches the near-UV excitation of InGaN chip(365 nm)for white-light-emitting diodes(w-LEDs),and emits 695 nm red light.A bright red emission peak is found in the PL spectrum and attributed to the spin-forbidden 2Eg?4A2 transition of Mn4+ ions.All decay times are in the range of microseconds,indicating a forbidden character of intra-d-shell transitions in Mn4+.The quantum efficiency of BLZT:0.0025Mn4+phosphor is determined to be 16.1%.The parameters of the obtained w-LED device are determined to be as follows:luminous efficiency,0.21 lm/W;CRI,81.2;and CCT,3803 K.All these results indicate that the samples can be applied in W-LEDs.(3)A deep-red-emitting Ca2LaNbO6:Mn4+(CLN:Mn4+)phosphor was synthesized by high-temperature solid-state reaction method.No traces of impurity phases are observed in the XRD patterns,and all diffraction peaks match well with those of the monoclinic phase Ca2LaTaO6.The UV-vis spectra showed that the doping of Mn4+ ions play a significant effect on the band gap of the CLN hosts.Excitation spectra showed two broad excitation peaks(358 and 518 nm),which can be attributed to the near-UV emitting InGaN chip.An obvious emission peak centered at 685 nm due to the spin-forbidden and parity-forbidden 2E?4A2g transition of the Mn4+ ions.CLN:Mn4+ phosphor showed temperature quenching from 298 K to 498 K,and Ea calculation(0.315 eV)revealed that the sample had good thermal stability.The analysis results of the as-fabricated W-LEDs were determined to be CCT:4288 K,CRI:87.9,and luminous efficiency:0.53 lm/W.All these results indicate that the samples can be applied in W-LEDs.(4)A series of novel Ba2LaNbO6(BLN):Mn4+,Yb3+ phosphors were successfully synthesized through a high-temperature solid-state reaction.XRD analysis showed that the sample was pure phase,and Mn4+ could replace Nb5+ in the BLN lattice.The excitation peaks of the two samples were all located at 352 nm,indicating that the samples could be excited by commercial LED near UV chips.UV-vis spectra indicate Mn4+ exerts important effects on the absorption of the BLN host,but Yb3+ exerts little effect on the absorption of the BLN:Mn4+phosphors.The emission peak of Mn4+ centered at 677 nm matched the red light emission required for phototropism well,while that of Yb3+ centered at 998 nm matched the far-red light emission required for photomorphogenesis.The activation energy of Mn4+ in the BLN:Mn4+ phosphor was calculated to be approximately 0.462 eV,thus confirming the good thermal stability of the material.Analysis of fluorescence lifetimes proved the occurrence of energy transfer between Mn4+ and Yb3+.The results showed that BLN:Mn4+,Yb3+ is a phosphor that can potentially be applied to plant-cultivation LEDs. |
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