Abstract
Crystalline powders of Ln3+ doped LaPO4 (Ln=Nd, Gd, Dy, Ho, Er, Tm, Yb) have been synthesized to serve in a case study for linking doping homogeneity as determined by NMR to luminescent properties. Samples obtained via different synthesis methods act as examples of homo‐ and inhomogeneous doping. The sample quality was verified by X‐ray diffraction. The homogeneously doped samples show improved luminescent properties in terms of brightness and lifetime which is consistent with the interpretation that, NMR visibility curves probe the distribution of paramagnetic dopants on a similar length scale as necessary for an efficient energy transfer in crystalline phosphors i. e. between sensitizers and activators, and to killer sites. Thus “NMR homogeneity” as observed by visibility curves may serve as a tool to optimize luminescent materials.
Highlights
Paramagnetic dopants, especially the paramagnetic lanthanide ions, play an important role in various applications, for exampleY3Al5O12:Ce3 + is used as scintillator material,[1] Y2O3 : Eu3 + in cathode ray tubes,[2] Gd2O2S : Tb3 + as X-ray phosphor,[3]SrAl2O4 : Eu2 +,Dy3 + as long persistent phosphor[4] andY3Al5O12 : Nd3 + in solid-state lasers.[5]
Their doping homogeneity was evaluated by X-ray diffraction (XRD), i. e. by Rietveld refinement and Vegard’s law.[40]
For the samples obtained via a solid-state reaction a phase separation of LnPO4 and LaPO4 becomes evident at high doping concentration (x 0.2) from the powder diffractograms (Supporting Information Figure S5)
Summary
Paramagnetic dopants, especially the paramagnetic lanthanide ions, play an important role in various applications, for example. Y3Al5O12 : Nd3 + in solid-state lasers.[5] In case of the application scenario of light-converting phosphors, brightness, efficiency and lifetime are related to the local pair distance[6] and the effective dopant concentration,[7] which are both microscopically related to the dopant distribution. E. quantum yields, phosphors may suffer from concentration quenching[6,8] at high doping level which inhibits higher emission intensities. A homogeneous distribution of dopants ensures a high effective doping concentration while it avoids concentration quenching[6] at low doping concentration and improves quantum yields (Figure 1 and 2).
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