CaZnOS:Nd³⁺ Emits Tissue-Penetrating near-Infrared Light upon Force Loading

Abstract

Mechanoluminescent (ML) materials are mechano-optical converters that can emit light under an external mechanical stimulus. All the existing ML materials can only emit light from near ultraviolet to red, which is outside the near-infrared (NIR) windows desired for biomechanical imaging. No studies have been done on doping rare earth (RE) ions with photoluminescence (PL) in the NIR region into a compound to form a ML material that emits NIR light in response to an external force. Here, we show that doping RE ions with a NIR PL into an inorganic compound does not usually result in the formation of a NIR ML material, which can only be achieved in the combination of Nd ions and a CaZnOS compound among the combinations we studied. The newly discovered NIR ML material (CaZnOS:Nd) is biocompatible and can efficiently convert mechanical stress into NIR light over the first and second tissue-penetrating bioimaging window. Its NIR ML emission appeared at a very low force threshold (even when the material was shaken slightly), increased sensitively and linearly with the increase in the force (up to >5 kN), and could penetrate the tissue as deep as >22 mm to enable biomechanical detection. Such a force-responsive behavior is highly reproducible. Hence, CaZnOS:Nd is a new potential ultrasensitive biomechanical probe and expands the ML application horizons into in vivo bioimaging.

Near infrared mechanoluminescence from Sr3Sn2O7: Nd3+for in situ biomechanical sensor and dynamic pressure mapping

“…The refinement process also produced lattice parameters of a = 20.676 03 Å, b = 5.728 16 Å, c = 5.710 01 Å for Sr 2.99 Sn 2 O 7 : 0.01Nd 3+ . These parameters are smaller than a = 20.68 83 Å, b = 5.736 07 Å, c = 5.710 07 Å for the blank sample, which can be ascribed to the successful substitution of larger Sr 2+ sites (R Sr 2+ = 1.41 Å for CN = 9 where CN means coordination number) by smaller Nd 3+ ions (R Nd 3+ = 1.163 Å for CN = 9) . Figure C denotes a perovskite stacked crystal structure of Sr 3 Sn 2 O 7 .…”

“…Comparison between the experimental and calculated results confirms that the sample crystallizes into orthorhombic where CN means coordination number) by smaller Nd 3+ ions (R Nd 3+ = 1.163 Å for CN = 9). 22,23 Figure 1C The SEM images of Sr 3-x Sn 2 O 7 : xNd 3+ with different Nd 3+ contents are shown in Figure 2A-F. Large amounts of intertwined columnar polyhedra are attached to the grain surfaces, and the main grain size ranges from 0.3 to 10 μm. Energy-dispersive X-ray (EDX) data of Sr 2.99 Sn 2 O 7 : 0.01Nd 3+ depicted in Figure 2G confirm that the sample is composed of Sr, Sn, O, and Nd elements, and the elements distribute uniformly throughout the samples.…”

Trap-controlled mechanoluminescent materials

“…Once bonded, these ML composites simultaneously "feel" (sense) and "see" (image) changes in stress distribution at the contact between the structure and the ML sensor. Another requirement is that the intensity of the ML signal in the surface-attached ML composite material scales quantitatively with the amplitude and distribution of load/stress/strain in the target structure [7,15,16,[124][125][126][127][128][129][130][131][132][133]. Once demonstrated, the effectiveness of a mechano-optical skin can be further enhanced by integrating multiple types of ML particles within the polymer coating, each of which may emit a unique color corresponding to a particular energy range, or type of defect.…”

“…The emission spectra of ML materials in the first two categories are strongly influenced by the crystal field strength [223], and so the ML spectra may differ for different host lattices, even if these hosts are doped with the same luminescent ion. The third category of luminescent ions includes the trivalent lanthanide ions (Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ , Tb 3+ , Dy 3+ , Ho 3+ , Er 3+ , Tm 3+ and Yb 3+ ) that emit narrow emission peaks due to 4f-4f transitions -examples include (Ba,Ca)TiO 3 :Pr 3+ (red) [89], mCaO•Nb 2 O 5 :Pr 3+ (m = 1, 2 and 3) (red) [112], LiNbO 3 :Pr 3+ (red) [113], NaNbO 3 :Pr 3+ (red) [129,130] [124], and CaZ-nOS:Pr 3+ /Nd 3+ /Sm 3+ /Eu 3+ /Tb 3+ /Dy 3+ /Ho 3+ /Er 3+ /Tm 3+ /Yb 3+ (from violet to NIR) [108,111,125,131]. Because the internal 4f shell is shielded by the 5 s 2 and 5p 6 orbitals, the energy of the sharp emission bands associated with 4f-4f transition in this category of ML materials is not sensitive to the nature of the ligand [223].…”

Short-Term Non-Decaying Mechanoluminescence in Li2MgGeO4:Mn2+

“…Mechanoluminescent (ML) materials that can quantitatively convert mechanical stimuli into light emission have drawn great attention due to potential applications ranging from stress distribution visualization [1,2] and structural health diagnosis [3][4][5] to light sources [6][7][8][9][10][11][12][13] and anti-counterfeiting [14][15][16]. Dozens of inorganic ML materials with reproducible mechanoluminescence (ML) have been developed during the past two decades [17,18].…”