Large‐Scale Room‐Temperature Synthesis of the First Sb3+‐Doped Organic Ge(IV)‐Based Metal Halides with Efficient Yellow Emission for Solid‐State Lighting and Latent Fingerprint Detection

Organic–inorganic hybrid Ge(II)‐based metal halides have garnered significant interest due to their intriguing photophysical properties and environmentally friendly characteristics. However, challenges such as poor stability, low emission intensity, and a complex synthesis process have hindered their widespread application. In addressing these issues, a breakthrough in the large‐scale production of Sb3+‐doped Ge(IV)‐based metal halide (C13H14N3)2GeCl6 phosphors at room temperature through a straightforward solution method is presented. The synthesized compound exhibits a remarkable bright broad yellow emission band at 590 nm, boasting a photoluminescence quantum efficiency of 99.53 ± 0.06% the highest among Ge(IV)‐based metal halides. Notably, the introduction of Sb3+ induces the formation of Jahn–Teller‐like self‐trapped excitons in [SbCl6]3− species, attributable to lattice distortion and strong electron–phonon coupling. Consequently, Sb3+‐doped (C13H14N3)2GeCl6 demonstrates a large Stokes shift (221 nm) and a prolonged decay lifetime (3.06 μs). Furthermore, the Sb3+‐doped compound exhibits commendable chemical‐ and photostability, prompting exploration in applications such as white light‐emitting diodes and latent fingerprint detection. This work not only provides a practical approach for designing economically viable, environmentally friendly, and highly efficient emission phosphors but also paves the way for novel directions in their expanded application.


Introduction
In recent years, organic-inorganic hybrid lead halide perovskites (OIHLHPs) have garnered significant attention in applications such as light-emitting diodes, solar cells, lasers, and scintillators, due to their intriguing photoelectric properties. [1]The tunability of the structural dimension in OIHLHPs, facilitated by a diverse range of organic ligands, has further fueled the advancement of perovskite materials in optoelectronic devices.Despite their progress in this field, [2] the toxicity of lead and their poor stability pose limitations to their commercial viability.Hence, there is an urgent need to explore nontoxic and environmentally friendly alternatives to replace OIHLHPs.
Recognizing that Sn 2þ and Ge 2þ belong to the same main group IVA as Pb 2þ , and exhibit low toxicity, they have emerged as promising candidates for substitution.The chemical properties and coordination configurations of these main group elements are similar, making Sn 2þ and Ge 2þ excellent contenders for replacing Pb 2þ .Recently, Sn(II)-based and Ge(II)-based metal halides have demonstrated remarkable results in optoelectronic devices due to Organic-inorganic hybrid Ge(II)-based metal halides have garnered significant interest due to their intriguing photophysical properties and environmentally friendly characteristics.However, challenges such as poor stability, low emission intensity, and a complex synthesis process have hindered their widespread application.In addressing these issues, a breakthrough in the large-scale production of Sb 3þ -doped Ge(IV)-based metal halide (C 13 H 14 N 3 ) 2 GeCl 6 phosphors at room temperature through a straightforward solution method is presented.The synthesized compound exhibits a remarkable bright broad yellow emission band at 590 nm, boasting a photoluminescence quantum efficiency of 99.53 AE 0.06% the highest among Ge(IV)-based metal halides.Notably, the introduction of Sb 3þ induces the formation of Jahn-Teller-like self-trapped excitons in [SbCl 6 ] 3À species, attributable to lattice distortion and strong electron-phonon coupling.Consequently, Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 demonstrates a large Stokes shift (221 nm) and a prolonged decay lifetime (3.06 μs).Furthermore, the Sb 3þ -doped compound exhibits commendable chemical-and photostability, prompting exploration in applications such as white light-emitting diodes and latent fingerprint detection.This work not only provides a practical approach for designing economically viable, environmentally friendly, and highly efficient emission phosphors but also paves the way for novel directions in their expanded application.their outstanding photophysical properties.For instance, the 2D compound (C 8 H 17 NH 3 ) 2 SnBr 4 exhibits intense emission and has been developed as a scintillator with exceptional radioluminescence intensity. [3]Another example is the 0D compound (C 4 N 2 H 14 Br) 4 SnBr 3 I 3 , which emits broadband yellow light upon photoexcitation and has been employed as a downconversion phosphor for solid-state lighting (SSL). [4]In a parallel context, 0D (1-mpz)GeBr 4 displays orange emission, while Bmpip 2 GeBr 4 exhibits near-infrared emission. [5]Numerous organic Sn(II)-based and Ge(II)-based metal halides and appear to be ideal substitutes for OIHLHPs.However, the susceptibility of Sn 2þ and Ge 2þ to oxidation in the air environment, leading to a þ4 oxidation state, results in luminescence quenching and poses a challenge to their widespread application.
Over the past few years, emphasis has been placed on organic Sn(IV)-based metal halides due to their commendable stability.However, their poor emission intensity attributed to the stereochemically inactive nature of Sn 4þ with a 4d 10 5s 0 outer-shell electron configuration and low radiation recombination rate necessitates further improvement. [6]Metal ion doping has proven effective in regulating the optical properties of the host matrix.Consequently, Sb 3þ with a 5s 2 electron configuration has been introduced into organic Sn(IV)-based compounds, leading to significant advancements.For example, Sb 3þ -doped (C 10 H 16 N 2 )SnCl 6 exhibits red emission with a photoluminescence quantum efficiency (PLQE) of 77%, [7] and Sb 3þ -doped (C 13 H 30 N) 2 SnCl 6 produces an efficient tunable white emission with near-unity PLQE. [8]Moreover, all Sb 3þ -doped organic Sn(IV)-based compounds showcased outstanding stability, enabling their further application in SSL, fluorescence anticounterfeiting, information encryption, and other related fields.
Given the effective luminescence observed in Sb 3þ -doped organic Sn(IV)-based metal halides, this approach appears promising for Ge(IV)-based metal halides as well.Building on this concept, we successfully developed the first Sb 3þ -doped Ge(IV)-based metal halide as a high-efficiency phosphor through a straightforward large-scale synthesis process at room temperature (RT).Upon photoexcitation, Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 exhibits a broadband yellow emission peaking at 590 nm with a full width at half-maximum (FWHM) of 180 nm, which should originate from the self-trapped excitons (STE) emission in the [SbCl 6 ] 3À species.Notably, the as-synthesized compound displayed a remarkable stability and an ultrahigh PLQE of 99.53 AE 0.06%.Finally, the applications of this compound were demonstrated in high-performance white light-emitting diodes (WLEDs) and latent fingerprint (LFP) detection.In summary, the synthesized Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 phosphors exhibit great potential for advanced optical applications.

Large-Scale Synthesis
In this work, we developed a simple large-scale synthesis process to synthesize Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 phosphors.In the air environment, the entire synthesis process only takes a few minutes at RT, and this method allows for the large-scale synthesis of ≈10.56 g with a yield of 80% for Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 phosphors in one time.Generally, the traditional hydrothermal and antisolvent recrystallization methods require high temperature (160-200 °C), toxic organic solvents (e.g., DMSO, DMF, and diethyl ether), or long reaction time (>24 h).In contrast, our synthesis process has unparalleled advantages, which lays a solid foundation for the further applications of lead-free metal halide phosphors.The detailed large-scale synthesis process of Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 phosphors is given in Figure 1a.When C 13 H 13 N 3 hydrochloric acid solution is quickly dropped into a mixed HCl solution containing corresponding molar ratios of GeO 2 and SbCl 3 , the powder precipitates appear immediately within a few minutes and shows efficient yellow emission under photoexcitation (Figure 1a, right).

Crystal Structure
The crystal structure analysis of (C 13 H 14 N 3 ) 2 GeCl 6 was performed using single-crystal (SC) X-ray diffraction (SCXRD), and the results are presented in Figure 1b.(C 13 H 14 N 3 ) 2 GeCl 6 crystallizes in the trigonal system with the R3 space group.The corresponding lattice parameters are a = 16.2646 ( 16) Å, b = 16.2646 ( 16) Å, c = 14.2518 (13) Å, and V = 3265.0(7) Å 3 .The Ge─Cl bond length ranged from 2.416 to 2.435 Å, while the Cl─Ge─Cl bond angle ranged from 87.18°to 94.15°.The crystal structure of (C 13 H 14 N 3 ) 2 GeCl 6 revealed that the [GeCl 6 ] 2À anions and the surrounding organic cations of C 13 H 14 N 3 þ were bonded together through ionic interactions.The unit cell contained two organic cations and one [GeCl 6 ] 2À cluster, where each germanium atom coordinates with six chlorine atoms to form an octahedral structure.Importantly, the [GeCl 6 ] 2À clusters were encapsulated by the surrounding organic cations, leading to the classification of (C 13 H 14 N 3 ) 2 GeCl 6 as a typical 0D ionic crystal at the molecular level (Figure 1b).In this 0D compound, the Ge-Ge distance was ≈10.47 Å, indicating the absence of significant Ge-Ge interactions (Figure S1, Supporting Information).The experimental powder X-ray diffraction (PXRD) pattern of pure (C 13 H 14 N 3 ) 2 GeCl 6 is provided in Figure S2, Supporting Information, consistent with the simulated results from SCXRD.
Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 was synthesized by introducing a small quantity of SbCl 3 into the precursor.Figure S3, Supporting Information, displays the crystal structure of Sb 3þdoped (C 13 H 14 N 3 ) 2 GeCl 6 , with the dopant occupying the Ge site due to their similar atomic radii.Comparative analysis with the pure sample reveals an identical PXRD profile for the Sb 3þdoped (C 13 H 14 N 3 ) 2 GeCl 6 (Figure 1c), confirming the phase purity of Sb 3þ -doped samples.Furthermore, the diffraction peak of the Sb 3þ -doped sample shifted to a lower angle, attributed to lattice expansion, as the ionic radius of Ge 4þ (r = 0.53 Å, CN = 6) is smaller than that of Sb 3þ (r = 0.76 Å, CN = 6).The scanning electron microscopy (SEM) image of Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 microcrystals is presented in Figure S4, Supporting Information, and the elemental mapping indicated a homogeneous distribution of Sb 3þ on the crystal surface.Additionally, energy-dispersive X-ray spectroscopy (EDS) results confirm the incorporation of Sb 3þ into the host lattice (Table S1, Supporting Information).X-ray photoelectron spectroscopy (XPS) analysis of Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 powders is shown in Figure S5, Supporting Information, revealing distinct characteristic peaks for Ge and Sb and further supporting the successful doping of Sb ions into (C 13 H 14 N 3 ) 2 GeCl 6 .Notably, a characteristic band at 34.1 eV in Figure S5b, Supporting Information, confirmed the presence of Ge 4þ in (C 13 H 14 N 3 ) 2 GeCl 6 . [9]

Optical Properties
In subsequent experiments, we conducted a thorough investigation of the optical properties of the samples.Pure (C 13 H 14 N 3 ) 2 GeCl 6 did not exhibit light emission under photoexcitation (Figure S6, Supporting Information).In sharp contrast, Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 phosphors displayed yellow emission under 365 nm excitation (Figure 1a, right).The RT optical properties of Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 phosphors are presented in Figure 2. The photoluminescence excitation (PLE) spectrum revealed a robust excitation band at 369 nm (Figure 2a).Under 369 nm excitation, the compound emitted a broadband yellow emission at 590 nm with FWHM of 180 nm.Consequently, this compound exhibits a substantial Stokes shift of 221 nm, indicating a negligible self-absorption in Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 .Figure S7, Supporting Information, shows the Sb 3þ doping concentration-dependent photoluminescence (PL) spectra, which exhibit a similar spectral characteristic.As the concentration of Sb 3þ increases from 5% to 20%, the PL intensity strengthens due in [SbCl 6 ] 3À luminescence centers.However, at higher Sb 3þ doping concentrations, the PL intensity diminishes due to concentration quenching. [10]tably, the 15%Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 exhibited the strongest emission accompanied by a remarkable PLQE of 99.53 AE 0.06% (Figure S8, Supporting Information).To the best of our knowledge, this represents the highest PLQE reported for Ge-based metal halides.The CIE coordinate of 15%Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 is situated at (0.47, 0.49), corresponding to yellow emission (Figure 2b).The absorption spectra of pristine and 15%Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 are illustrated in Figure S9, Supporting Information, and Figure 2c, respectively.For (C 13 H 14 N 3 ) 2 GeCl 6 , a strong absorption in the 250-310 nm range was observed, corresponding to the electronic transition from the valence band to the conduction band.After Sb 3þ doping, a notable low-energy absorption band at 370 nm emerged, attributed to the 1 S 0 -to-3 P 1 transition of Sb 3þ , correlating with the PLE spectrum of Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 (Figure 2a). [11]The experimental bandgap values of pure (C 13 H 14 N 3 ) 2 GeCl 6 and Sb 3þ -doped compounds were determined to be 2.61 and 2.35 eV, respectively.The significant decrease in the bandgap after Sb 3þ doping indicated an extended absorption range.
Further experiments were conducted to investigate the intrinsic emission mechanism of Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 .The excitation power-dependent PL spectra of the Sb 3þ -doped compound are shown in Figure S10a, Supporting Information, revealing a linear relationship between PL intensity and excitation power (Figure S10b, Supporting Information), ruling out the possibility of broadband emission in Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 stemming from permanent defects. [12]oreover, PL spectra under various excitation wavelengths exhibited similar characteristics (Figure S11, Supporting Information), and the PLE spectra monitored at 550-600 nm displayed an identical profile (Figure S12, Supporting Information).Consequently, the broad yellow emission in Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 was attributed to the same excited state.The PL decay lifetime of 15%Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 is presented in Figure 2d, fitting well with a monoexponential function based on its exciton radiation characteristics.The decay lifetime of this compound is 3.06 μs, indicating that the yellow emission is phosphorescence emission. [13]Based on these findings, the yellow broadband emission in Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 is a typical STE emission, a phenomenon reported in other Sb 3þ -doped systems. [14]

Photophysical Mechanism
The temperature-dependent PL spectra (80-300 K) of 15%Sb 3þdoped (C 13 H 14 N 3 ) 2 GeCl 6 were acquired under 310 excitation (Figure 3a).The PL intensity gradually increased as temperature decreased from 300 to 80 K, indicating the suppression of nonradiative transitions at lower temperatures.Additional insights into the temperature-dependent behavior are provided by Figure S13 and S14, Supporting Information, which present the PL peak position and FWHM of Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 under various temperatures.Notably, as the temperature increases, the emission peak position shows a continuous blueshift, and the same phenomenon was found in other lead-free compounds with broadband emission of (NII) 2 SbCl 5 [15]   and TTA 2 InCl 5 : Sb 3þ . [16]This shift was attributed to the lattice deformation and changes in the valence band with temperature. [17]Furthermore, the FWHM of the yellow emission band broadened at higher temperatures, suggesting an increase in electron-phonon coupling. [18]Subsequently, the activation energy (E a ) of Sb 3þ -doped sample was calculated using Equation (1). [19]T where I 0 is the PL intensity at 0 K, and k B is the Boltzmann constant.Based on the fitting results in Figure 3b, the activation energy (E a ) of Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 is 61 meV.In general, nonradiative transitions occur when the excited electrons reach the crossing point of 1 S 0 and STE states, leading to the thermal quenching of STE emission (Figure 3d).Importantly, the calculated E a for Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 is significantly larger than the RT thermal ionization energy (26 meV), as reported in a previous study. [20]This substantial difference in energy values indicates that it is challenging for electrons to overcome the energy barriers and undergo nonradiative relaxation.Therefore, the photogenerated excitons in Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 can remain stable at RT, resulting in efficient yellow emission. [21]he strength of electron-phonon coupling can be reflected by the Huang-Rhys factor (S), which is calculated by fitting the FWHM versus temperature using Equation (2). [22]gure 2. a) PLE and PL spectra of 15%Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 .b) CIE coordinate of (C 13 H 14 N 3 ) 2 GeCl 6 : 15%Sb 3þ .c) The absorption spectrum and the Tauc plot of 15%Sb 3þ doped-(C 13 H 14 N 3 ) 2 GeCl 6 .d) Time-resolved PL spectrum of 15%Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 monitored at 590 nm.where ω phonon is phonon frequency, and the calculated S value of Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 is 19.58 (Figure 3c).Notably, this S value is comparable to that of some 0D metal halides known for efficient STE emission, [23] indicating a significant electronphonon interaction in Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 , which plays a crucial role in the favorable formation of STEs.Subsequently, we conducted Raman spectroscopy on (C 13 H 14 N 3 ) 2 GeCl 6 : 15%Sb 3þ to further explore the impact of electron-phonon coupling on STEs (Figure S15, Supporting Information).Typically, Raman vibrations in the range of 50-500 cm À1 primarily arise from inorganic lattices.Additionally, the characteristic peaks at 86 and 160 cm À1 can be attributed to the intramolecular liberation and bending of SbCl 3 , [24] indicating the successful incorporation of Sb 3þ ions into the GeCl 4 lattice.Furthermore, Raman peaks at 160, 222, 246, and 415 cm À1 can be considered as overtones and sum frequencies of the bands at 86 and 160 cm À1 .These results substantiate the presence of a strong anharmonic electron-phonon interaction in the Sb 3þ -doped compound.This unique phonon spectral feature provides compelling evidence for the formation of STEs. [25]t is now understood that 0D metal halides typically exhibit a significant separation between metal halide clusters, indicating negligible interaction.Consequently, the emission in 0D crystals is expected to originate from independent inorganic halide polyhedra, such as [SnCl 3 ] À , [25a] [MnBr 4 ] 2À , [26] and [Cu 2 I 4 ] 2À . [27]In the case of our Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 system, the broad yellow emission was attributed to [SbCl 6 ] 3À centers, as the pure Ge(IV)-based compound does not emit light.Based on the aforementioned results, the excited-state dynamic processes of Sb 3þdoped (C 13 H 14 N 3 ) 2 GeCl 6 are illustrated in Figure 3d.Upon photoexcitation (e.g., 369 nm), electrons within the [SbCl 6 ] 3À clusters transition from the ground state ( 1 S 0 ) to the excited state ( 3 P 1 ).The photogenerated excitons rapidly underwent self-trapping due to strong electron-phonon coupling.Subsequently, STEs tend to experience intersystem crossing, transitioning from the excited state to the STE state.Consequently, the broad yellow emission in Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 was observed when STEs returned to the ground state.

Stabilities and Applications
The stability of materials plays a crucial role in determining their suitability for various applications.In our investigations, we explored the stability of the synthesized compounds using 15%Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 as a representative example.Figure S16, Supporting Information, presents the thermogravimetric analysis of 15%Sb 3þ -doped sample, revealing a decomposition temperature of 200 °C.After two months of exposure to air, the sample exhibited a PXRD pattern similar to the fresh sample (Figure S17a, Supporting Information), with only a 7% reduction in emission intensity (Figure S17b, Supporting Information).This remarkable air stability of the as-synthesized Sb 3þ -doped phosphors can be attributed to the high valence states of Sb and Ge, making them less prone to oxidation.25b] Subsequently, the synthesized 15%Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 was utilized as a down-conversion phosphor and applied to SSL.Specifically, we mixed the yellow-emitting (C 13 H 14 N 3 ) 2 GeCl 6 : 15%Sb 3þ with the blue phosphor BaMgAl 10 O 17 : Eu 2þ and coated them on a commercial 365 nm chip.Figure 4a illustrates the electroluminescence (EL) spectrum of the WLED, and the inset shows optical images of the device.The device exhibited efficient warm-white emission with a Commission Internationale de I'Eclairage (CIE) color coordinate of (0.36, 0.32), a correlated color temperature (CCT) of 4502 K, and a color-rendering index (CRI) of 92.9 (Figure 4b), Notably, the CRI value is significantly higher than that of other 0D metal halides-based WLEDs (such as Cs 2 ZrCl 6 : Bi 3þ /Te 4þ (85.1), [28] (TEA) 2 InCl 5 : Sb 3þ (85.1), [23c] and Cs 3 Cu 2 I 5 (82.4) [29] ).This high CRI ensures outstanding color reproduction in the fabricated WLED (Figure S19, Supporting Information).Moreover, the EL spectra at different driving currents exhibit consistent profiles, indicating excellent color stability of the device (Figure 4c).
Additionally, the luminous efficiency of the device remained essentially unchanged after running for 240 min (Figure 4d).Therefore, these results underscore the excellent potential of (C 13 H 14 N 3 ) 2 GeCl 6 : Sb 3þ in SSL applications.
In recent years, LFP detection has extensively been used in medical diagnosis, national security, access control, and forensic investigation. [30]Formed by the secretion of sweat from sweat pores when fingers touch objects, LFPs often persist even after thorough hand drying, especially on smooth surfaces.These fingerprints, invisible to the naked eye, are a common type found at crime scenes.Luminescent materials have been increasingly employed for LFP visualization, including CdS quantum dots [31] and perovskite nanocrystals. [30]However, the complex synthesis processes and high toxicity associated with some of these materials limit their applicability.In recent research, the Saparov group demonstrated that lead-free metal halides hold promise for LFP detection.Nevertheless, the low PLQE of these materials has hindered their effective use in visualization applications. [30,32]n the present study, the exceptional properties of 15%Sb 3þdoped (C 13 H 14 N 3 ) 2 GeCl 6 discussed earlier provide a solution to the limitations of the previously mentioned luminescent materials.A high-quality luminescent ink was created by uniformly dispersing Sb 3þ -doped phosphors in polydimethylsiloxane (PDMS), and its application in LFP detection was explored.Figure 5a displays a luminescent fingerprint created using luminescent ink on black cardboard, and the overall ridge features of the fingerprint can be witnessed clearly.In the locally enlarged images of LFPs (Figure 5b), the latent features of 1) bifurcation; 2) island; 3) core; 4) spur; 5) bridge; and 6) ridge ending can be observed clearly under 365 nm excitation.As each fingerprint is unique, the above is crucial for personal identification.Importantly, the naked eye visualization of these features highlights the significant application potential of 15%Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 in LFP detection.Furthermore, fingerprints were deposited on cardboards with different colors, as depicted in Figure 6a, demonstrating the ink's ability to retain good recognition features under various conditions.To illustrate the universality of 15%Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 ink in LFP detection, it was applied to surfaces of diverse materials, including a table, glass slide, and polyethylene transparent plastic bag (Figure 6b).Fingerprint visibility was confirmed on all substrates with the naked eye.To assess durability, the treated fingerprints on different substrates were exposed to ethanol, a commonly used disinfectant and cleaning agent, and remained visible under UV light (Figure 6c).Furthermore, the fabricated fingerprints demonstrated outstanding stability, retaining high-intensity emission even after two weeks of storage in the air (Figure 6d).Consequently, these results provide initial evidence for the reliability of Sb 3þ -doped Ge(IV)-based compound in the field of LFP detection.

Conclusion
In summary, we have reported a facile large-scale synthesis of Sb 3þ -doped 0D organic Ge(IV)-based metal halide phosphors at RT.The as-synthesized Sb 3þ -doped phosphors show broad yellow emission band at 590 nm with FWHM of 221 nm and a long decay lifetime of 3.06 μs, which should be attributed to the STE emission due to the lattice distortion and intense electronphonon coupling.Particularly, the Sb 3þ -doped Ge(IV)-based compound has an ultrahigh PLQE of 99.53 AE 0.06%, which is the highest value for organic Ge(IV)-based halides.Moreover, Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 phosphors also exhibit remarkable chemical and photostabilities, which enables us to further demonstrate their optical applications.Thus, a high-performance WLED was fabricated by combining yellow phosphors of Sb 3þdoped (C 13 H 14 N 3 ) 2 GeCl 6 with blue phosphors of BaMgAl 10 O 17 : Eu 2þ , which exhibits CIE color coordinate of (0.36, 0.32), CCT of 4502 K, and CRI of 92.9.Moreover, the LFP detection application based on Sb 3þ -doped (C 13 H 14 N 3 ) 2 GeCl 6 ink was also demonstrated.Our findings suggest that organic Ge(IV)-based compounds have excellent prospects in optoelectronic applications and are worthy of further development in the future.

Figure 4 .
Figure 4. a) EL spectrum of the prepared WLED.The inset shows the photos of the prepared WLED.b) CIE coordinate of the WLED.c) EL spectra under various drive currents.d) Operational stability of WLED.

Figure 6 .
Figure 6.a) The fingerprints deposited on the cardboards with different colors.b) The fingerprints are deposited on table, glass slide, and polyethylene transparent plastic bag, respectively.c) Optical images of fingerprints after treatment by ethanol under 365 nm excitation.d) Optical images of fingerprints stored in air for two weeks under 365 nm excitation.