Dynamics of the host-sensitization by energy transfer from the self-trapped excitons and fabrication of novel white phosphors

我们一直在寻找对稀土离子（Gd^<3+>, Tb^<3+>, Eu^<3+>和Pr^<3+>）具有增敏效应的新型真空紫外（VUV）激发材料，以实现白色荧光粉。在本研究中，我们研究了硼酸钪(LaSc_3（BO_3)_4 (LSB)）和磷酸盐(Li_3Sc_2 (PO_4)_3 (LSP), K_3Sc (PO_4)_2 (KSP), K_2CsSc（PO_4)_3 (KCSP)）和氟锆酸盐（LaZr_2F_11 (LZF)），其中宿主对VUV光的吸收可能导致有效的能量转移到稀土离子（Gd^<3+>, Tb^<3+>, Eu^<3+>和Pr^<3+>）。我们观察了自困激子（STE）向Gd^<3+>、Tb^<3+>和Eu^<3+>离子的能量转移，并确定了它们的动力学。在本研究中得到的结果如下。(1)发现硼酸钪(LaSc_3（BO_3)_4(LSB)）和磷酸盐(Li_3Sc_2(PO_4)_3（LSP）、K_3Sc(PO_4)_2（KSP）、K_2CsSc（PO_4)_3 (KCSP)）和氟锆酸盐（LaZr_2F_11(LZF)）在紫外可见区表现出寄主辐射，并测定了它们的寿命。宿主辐射被认为是由于BO_3^<3->或PO_4^<3->基团的带隙激发或分子内跃迁而产生的STEs。Gd^<3+>, Tb^<3+>和Eu^<3+>被宿主激发（STEs）的能量转移所敏化，并在这些材料中确定了它们的动力学。(2)在紫外激发下，未掺杂的LSB在315和366 nm处表现出本征宽发射带。在315 nm处峰值的主发射可以归因于STE的重组，这可能与带隙激发或BO_3^<3->基团的分子跃迁有关。在Gd^<3+>和Tb^<3+>掺杂样品（LSB: Gd和LSB: Tb）中，宿主发射随Gd^<3+>或Tb^<3+>浓度的增加而降低（5-50 at）。%)，这伴随着Gd^<3+>或Tb^<3+>跃迁的增加。这表明从宿主到Gd^<3+>离子的有效能量转移。此外，在Gd^<3+>-或Tb^<3+>-掺杂样品中，随着Gd^<3+>或Tb^<3+>浓度的增加，宿主发射的衰减时间减小。这一发现为LSB: Gd和LSB: Tb从STE到Gd^<3+>或Tb^<3+>的能量转移提供了进一步的证据。通过时间分辨测量，确定了从STE到Gd^<3+>和Tb^<3+>的能量转移率。这些观测到的速率在估计的偶极子-偶极子能量转移速率的一个数量级之内。确定了宿主排放物的温度依赖性。结果表明，从STE到Gd^<3+>和Tb^<3+>的能量转移可能是由于激子迁移而热激活的。(3) Gd^<3+>掺杂的LSP和KSP在VUV激发下也观察到自困激子（STE）的能量转移。宿主到gd ^<3+>的能量转移动力学。得到了主发射光谱（归属于STE）和激发光谱，以及在157 nm处激发的时间分辨发射光谱。从时间分辨测量，宿主的能量传输速率。到gd ^<3+>是确定的。从估计的偶极子-偶极子能量转移率与实验测量的辐射强度的温度依赖性比较，表明从STE到Gd^<3+>的热激活能量转移过程与LSB: Gd和LSB: Tb一样发生。(4) GdPO_4: Tb^<3+>和Sr_3Gd(PO_4)_3: Tb^<3+>和Na_2GdF_2PO_4: Tb^<3+>在主晶格和Tb^<3+> 4f^8-4f^7-5d激发下均观察到明显的量子切割。在Tb^<3+> 4f^75d态激发后，能量通过一对Tb^<3+>之间的交叉弛豫过程转移。Tb^<3+>和/或Tb^<3+>。Gd ^ < 3 + >;在VUV区主晶格激发后，激发能要么直接转移到4f^75d态的Tb^<3+>，要么先转移到Gd^<3+>的^6G能级，然后再转移到4f^75d态的Tb^<3+>，然后通过交叉弛豫能转移到Tb^<3+> 4f^7-5d态的弛豫能。在Na_2GdF_2PO_4: Eu_<3+>中观察到从Gd^<3+>到Eu^<3+>和Eu^<3+>到Eu^<3+>的有效能量转移。少

We have been searching for new vacuum ultraviolet (VUV)-excited materials that exhibit a sensitization effect for rare-earth ions (Gd^<3+>, Tb^<3+>, Eu^<3+>, and Pr^<3+>) toward realizing white phosphors. In this study, we investigate scandium borate (LaSc_3(BO_3)_4 (LSB)) and phosphates (Li_3Sc_2 (PO_4)_3 (LSP), K_3Sc (PO_4)_2 (KSP), K_2CsSc(PO_4)_3 (KCSP)), and fluorozirconate (LaZr_2F_11 (LZF)), in which the absorption of VUV light by the host may lead to efficient energy transfer to rare-earth ions ( Gd^<3+>, Tb^<3+>, Eu^<3+> , and Pr^<3+> ). We observed energy transfer from the self-trapped exciton (STE) to Gd^<3+>, Tb^<3+>, and Eu^<3+> ions and we determined their dynamics. In this research the results obtained are as follows.(1) Scandium borate (LaSc_3(BO_3)_4(LSB)) and phosphates(Li_3Sc_2(PO_4)_3(LSP), K_3Sc(PO_4)_2(KSP), K_2CsSc(PO_4)_3 (KCSP)), and fuluorozirconate (LaZr_2F_11(LZF)) have been found to exhibit host emission in the UV-visible region and the lifetimes of these h … More ost emissions have been determined. The host emissions have been ascribed to STEs which are derived from band gap excitations or intramolecular transitions of the BO_3^<3-> or PO_4^<3-> group. Sensitizations of the Gd^<3+>, Tb^<3+>, and Eu^<3+> by energy transfer from the host excitations (STEs) have been demonstrated and their dynamics have been determined in these materials.(2) Under VUV-excitation, undoped LSB exhibits intrinsic broad emission bands at 315 and 366 nm. The host emission with a peak at 315 nm can be assigned to recombination of the STE that could be associated with band-gap excitations or molecular transitions with the BO_3^<3-> group. In Gd^<3+>-and Tb^<3+>-doped samples (LSB : Gd and LSB : Tb), host emission decreases with increasing Gd^<3+> or Tb^<3+> concentration (5-50 at.%) and this is accompanied by an increase in the transition of Gd^<3+> or Tb^<3+>. This suggests efficient energy transfer from the host to Gd^<3+> ions. In addition, in the Gd^<3+>-or Tb^<3+>-doped samples the decay time of the host emission decreases with increasing Gd^<3+> or Tb^<3+> concentration. This finding provides further evidence for energy transfer from the STE to Gd^<3+> or Tb^<3+> in LSB : Gd and LSB : Tb. From time-resolved measurements, the energy transfer rates from the STE to Gd^<3+> and Tb^<3+> were determined. These observed rates are within an order of magnitude of the estimated dipole-dipole energy transfer rates. The temperature dependences of the host emissions were determined. It was demonstrated that the energy transfers from STE to Gd^<3+> and Tb^<3+> are thermally activated probably due to exciton mobility.(3) Energy transfer from the self-trapped excitons (STE) upon VUV excitation was also observed in Gd^<3+>-doped LSP and KSP. The dynamics of the host-to-Gd^<3+> energy transfer. The host emission (ascribed to STE) and excitation spectra, as well as time-resolved emission excited at 157 nm were obtained. From time-resolved measurements, the energy transfer rate of the host.to-Gd^<3+> are determined. From a comparison of estimated dipole-dipole energy transfer rate with the experimentally measured temperature dependence of emission intensity, it was suggested that a thermally activated energy transfer process from the STE to Gd^<3+> occurs as with LSB : Gd and LSB : Tb.(4) Visible quantum cutting was observed in GdPO_4 : Tb^<3+> and Sr_3Gd(PO_4)_3 : Tb^<3+>, and Na_2GdF_2PO_4 : Tb^<3+> upon the host lattice and Tb^<3+> 4f^8-4f^7-5d excitations. Upon excitation at the Tb^<3+> 4f^75d state, then energy transfers via a cross relaxation process between a pair of Tb^<3+>.Tb^<3+> and/or Tb^<3+>.Gd^<3+> ; upon host lattice excitation in the VUV region, the excitation energy either directly transfers to a Tb^<3+> in its 4f^75d state or first transfer to the ^6G level of Gd^<3+> then to Tb^<3+> in its 4f^75d state, then relaxes via cross relaxation energy transfer as that excited at Tb^<3+> 4f^7-5d state. An efficient energy transfer from Gd^<3+> to Eu^<3+> and Eu^<3+> to Eu^<3+> was observed in Na_2GdF_2PO_4 : Eu_<3+>. Less