Doping homogeneity in co-doped materials investigated at different length scales

Li, Wenyu; Smet, Philippe; Martin, Lisa I. D. J.; Pritzel, Christian; Günne, Jörn Schmedt auf der

doi:10.1039/c9cp05599a

Cited by 9 publications

(7 citation statements)

References 42 publications

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“…The concentration-dependent PL study indicates that the intensity of the IR emission scales with the product of the concentrations of both dopants; however, drawing quantitative conclusions is hindered by the limited number of concentrations that can be prepared and does not account for uncontrollable microscopic concentration differences 47 – 50 . To get a more detailed picture, a microscopic study is performed.…”

Section: Resultsmentioning

confidence: 99%

Broadband infrared LEDs based on europium-to-terbium charge transfer luminescence

Joos¹,

Heggen²,

Martin³

et al. 2020

Nat Commun

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123

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Efficient broadband infrared (IR) light-emitting diodes (LEDs) are needed for emerging applications that exploit near-IR spectroscopy, ranging from hand-held electronics to medicine. Here we report broadband IR luminescence, cooperatively originating from Eu 2+ and Tb 3+ dopants in CaS. This peculiar emission overlaps with the red Eu 2+ emission, ranges up to 1200 nm (full-width-at-half-maximum of 195 nm) and is efficiently excited with visible light. Experimental evidence for metal-to-metal charge transfer (MMCT) luminescence is collected, comprising data from luminescence spectroscopy, microscopy and X-ray spectroscopy. State-of-the-art multiconfigurational ab initio calculations attribute the IR emission to the radiative decay of a metastable MMCT state of a Eu 2+ -Tb 3+ pair. The calculations explain why no MMCT emission is found in the similar compound SrS:Eu,Tb and are used to anticipate how to fine-tune the characteristics of the MMCT luminescence. Finally, a near-IR LED for versatile spectroscopic use is manufactured based on the MMCT emission.

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Section: Resultsmentioning

confidence: 99%

Broadband infrared LEDs based on europium-to-terbium charge transfer luminescence

Joos¹,

Heggen²,

Martin³

et al. 2020

Nat Commun

Self Cite

123

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“…Given the only slightly smaller ionic radius of Nd 3+ (1.163 Å for nine-fold coordination) compared to that of La 3+ (1.216 Å for ninefold coordination) [62], a full range of solubility of NdPO4 within the LaPO4 host is expected. Synthesis of the solid solutions La1-xNdxPO4 by a co-precipitation approach instead conventional heterogeneous mixing and subsequent thermal annealing permits a more random distribution of the Nd 3+ activators substituting for the La 3+ ions, as has also been recently independently established by solid state magic angle spinning nuclear magnetic resonance (MAS-NMR) experiments on the 31 P nuclei in lanthanide-activated LaPO4, whose resonances sensitively react on paramagnetic impurities in their close environment [63][64][65]. Figure 1a depicts the XRPD patterns of the Nd 3+ -activated LaPO4 nanocrystals as prepared by the hydrothermal co-precipitation approach.…”

Section: Structural and Morphological Characterization Of The Nd 3+ -mentioning

confidence: 98%

Making Nd3+ a Sensitive Luminescent Thermometer for Physiological Temperatures—An Account of Pitfalls in Boltzmann Thermometry

et al. 2020

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Ratiometric luminescence thermometry employing luminescence within the biological transparency windows provides high potential for biothermal imaging. Nd3+ is a promising candidate for that purpose due to its intense radiative transitions within biological windows (BWs) I and II and the simultaneous efficient excitability within BW I. This makes Nd3+ almost unique among all lanthanides. Typically, emission from the two 4F3/2 crystal field levels is used for thermometry but the small ~100 cm−1 energy separation limits the sensitivity. A higher sensitivity for physiological temperatures is possible using the luminescence intensity ratio (LIR) of the emissive transitions from the 4F5/2 and 4F3/2 excited spin-orbit levels. Herein, we demonstrate and discuss various pitfalls that can occur in Boltzmann thermometry if this particular LIR is used for physiological temperature sensing. Both microcrystalline, dilute (0.1%) Nd3+-doped LaPO4 and LaPO4: x% Nd3+ (x = 2, 5, 10, 25, 100) nanocrystals serve as an illustrative example. Besides structural and optical characterization of those luminescent thermometers, the impact and consequences of the Nd3+ concentration on their luminescence and performance as Boltzmann-based thermometers are analyzed. For low Nd3+ concentrations, Boltzmann equilibrium starts just around 300 K. At higher Nd3+ concentrations, cross-relaxation processes enhance the decay rates of the 4F3/2 and 4F5/2 levels making the decay faster than the equilibration rates between the levels. It is shown that the onset of the useful temperature sensing range shifts to higher temperatures, even above ~ 450 K for Nd concentrations over 5%. A microscopic explanation for pitfalls in Boltzmann thermometry with Nd3+ is finally given and guidelines for the usability of this lanthanide ion in the field of physiological temperature sensing are elaborated. Insight in competition between thermal coupling through non-radiative transitions and population decay through cross-relaxation of the 4F5/2 and 4F3/2 spin-orbit levels of Nd3+ makes it possible to tailor the thermometric performance of Nd3+ to enable physiological temperature sensing.

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“…The NMR relaxation behavior as a function of the dopant concentration can be used to assess the homogeneity of the dopant in the sample. − In the glass we see a nearly inverse squared dependence of the T 1 and T 2 relaxation times with the Gd(III) concentration as one would expect for homogeneous doping in the absence of spin diffusion . On the other hand, a significant weaker, shortening of T 1 with dopant concentration is observed for 29 Si and 6 Li in the crystalline system, with approximately T 1 ∝ [Gd] −1.5 and [Gd] −1 , respectively.…”

Section: Resultsmentioning

confidence: 83%

The Effect of Disorder on Endogenous MAS-DNP: Study of Silicate Glasses and Crystals

et al. 2023

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In dynamic nuclear polarization nuclear magnetic resonance (DNP-NMR) experiments, the large Boltzmann polarization of unpaired electrons is transferred to surrounding nuclei, leading to a significant increase in the sensitivity of the NMR signal. In order to obtain large polarization gains in the bulk of inorganic samples, paramagnetic metal ions are introduced as minor dopants acting as polarizing agents. While this approach has been shown to be very efficient in crystalline inorganic oxides, significantly lower enhancements have been reported when applying this approach to oxide glasses. In order to rationalize the origin of the difference in the efficiency of DNP in amorphous and crystalline inorganic matrices, we performed a detailed comparison in terms of their magnetic resonance properties. To diminish differences in the DNP performance arising from distinct nuclear interactions, glass and crystal systems of similar compositions were chosen, Li2OCaO·2SiO2 and Li2CaSiO4, respectively. Using Gd(III) as polarizing agent, DNP provided signal enhancements in the range of 100 for the crystalline sample, while only up to around factor 5 in the glass, for both 6Li and 29Si nuclei. We find that the drop in enhancement in glasses can be attributed to three main factors: shorter nuclear and electron relaxation times as well as the dielectric properties of glass and crystal. The amorphous nature of the glass sample is responsible for a high dielectric loss, leading to efficient microwave absorption and consequently lower effective microwave power and an increase in sample temperature which leads to further reduction of the electron relaxation time. These results help rationalize the observed sensitivity enhancements and provide guidance in identifying materials that could benefit from the DNP approach.

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Doping homogeneity in co-doped materials investigated at different length scales

Abstract: Doping homogeneity is important for the properties of co-doped phosphors, as it can affect the energy transfer between sensitizer and activator ions.

Cited by 9 publications

References 42 publications

Broadband infrared LEDs based on europium-to-terbium charge transfer luminescence

Broadband infrared LEDs based on europium-to-terbium charge transfer luminescence

Making Nd3+ a Sensitive Luminescent Thermometer for Physiological Temperatures—An Account of Pitfalls in Boltzmann Thermometry

The Effect of Disorder on Endogenous MAS-DNP: Study of Silicate Glasses and Crystals

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