Rapid Nondestructive Detection Enabled by an Ultra‐Broadband NIR pc‐LED

Abstract

The rapid development of near‐infrared (NIR) spectroscopic techniques has greatly stimulated the discovery of novel broadband NIR‐emitting phosphors as advanced light sources. Herein, a novel double‐perovskite phosphor La2MgHfO6:Cr3+/Yb3+ that displays ultra‐broadband NIR emissions with a full‐width at half maximum (FWHM) of 333 nm is reported. The remarkable luminescence property stems from the multiple crystallographic sites, relatively weak crystal field, and efficient Cr3‐to‐Yb3+ energy transfer (ET). The site occupation of Cr3+ is elaborately verified by the Rietveld refinement and first‐principles calculation. By controlling the ET process, the internal/external quantum efficiency (IQE/EQE), bandwidth, and thermal stability of NIR emissions are substantially improved. The as‐prepared phosphors are further integrated into a miniaturized NIR light‐emitting diode (LED) package, demonstrating superior performance in rapid nondestructive detection of structural failure in thin electronic cables. The results described here provide a novel pointcut for designing broadband NIR‐emitting phosphors with desired optical properties toward applications in industrial inspection and medical diagnosis.

Efficient and Thermally Robust Broadband Near‐Infrared Emission in a Garnet Ca3MgHfGe3O12:Cr3+ Phosphor

“…The signals with binding energies at 348, 124, 17, 32, and 531 eV, should be assigned to Ca-2p, Mg-2p, Hf-4f, Ge-3d, and O-1s, respectively; while the signal peak corresponding to Cr-2p appears at 578 eV, indicating that only trivalent Cr ions are presented in this sample without a secondary valence state. [36] These results confirmed the elemental composition of this sample as expected, and suggest that the valence state of Cr 3+ can be perfectly self-balanced when simultaneously cosubstituting Mg 2+ and Hf 4+ ions in octahedral site of this specific crystal structure (visualized as Figure 2e).…”

“…= 0.71 Å). [ 36 ] Moreover, the X‐ray photoelectron spectroscopy (XPS) as depicted in Figure 2d was adopted to examine the elemental composition and valence state of Ca 3 Mg 0.98 Hf 0.98 Cr 0.04 Ge 3 O 12 sample. The signals with binding energies at 348, 124, 17, 32, and 531 eV, should be assigned to Ca‐2p, Mg‐2p, Hf‐4f, Ge‐3d, and O‐1s, respectively; while the signal peak corresponding to Cr‐2p appears at 578 eV, indicating that only trivalent Cr ions are presented in this sample without a secondary valence state.…”

Enhanced Thermal Stability and Energy Transfer by Crystal‐Field Engineering in a Garnet Phosphor for Thermometry and NIR‐LED

“…The energy transfer efficiencies from the Cr 3+ to Yb 3+ or Nd 3+ ions are very close to the reported maximum values. [22] These results indicate that the energy transfer from Cr 3+ to Yb 3+ or Nd 3+ is more efficient in the stronger crystal field. Energy transfer can be applied to improve the sensitivity of optical thermometry, because of the temperate dependent energy transfer efficiency and the different thermal quenching behaviors between the luminescent ions.…”

Producing Tunable Broadband Near-Infrared Emission through Co-Substitution in (Ga1–xMgx)(Ga1–xGex)O3:Cr3+

“…Over the past several years, researchers have developed multiple workarounds to overcome the lack of optimal Cr 3+ coordination environments, including the “multiple-site strategy”, Cr 3+ -Yb 3+ energy transfer, and crystal field engineering, all of which have been applied to increase the coverage of long-wavelength NIR emission. − For example, La 3 Ga 5 GeO 14 :Cr 3+ and La 2 MgZrO 6 :Cr 3+ have full width at half maximum (FWHM) values of 330 and 210 nm, respectively, due to their multiple substitution sites. , Ca 2 LuZr 2 Al 3 O 12 :Cr 3+ ,Yb 3+ , La 2 MgHfO 6 :Cr 3+ ,Yb 3+ , LiIn 2 SbO 6 :Cr 3+ ,Yb 3+ , and LiScP 2 O 7 :Cr 3+ ,Yb 3+ each have a FWHM of over 210 nm benefiting from efficient Cr 3+ -Yb 3+ energy transfer. − Crystal field engineering was applied by forming solid solutions, like in Mg 2–2 x Li x Sc x GeO 4 :Cr 3+ , to shift the emission peak from 940 to 1110 nm and widen the corresponding FWHM from 236 to 300 nm . Although most of these strategies are effective, the basic way to regulate the luminescence properties of Cr 3+ -activated material still depends on controlling the strength of the crystal field.…”