Supporting Information

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1 Supporting Information Selective formation of gallium nitride quantum dots inside a zinc methylimidazolate framework Daniel Esken, a Stuart Turner, b Christian Wiktor, a,b Suresh Babu Kalidindi, a Gustaaf Van Tendeloo b a and Roland A. Fischer a Department of Inorganic Chemistry II, Ruhr-University Bochum, Bochum, Germany b Electron Microscopy for Materials Science (EMAT), University of Antwerp, 2020 Antwerp, Belgium General remarks Analytical instrumentation. All chemicals were purchased from commercial suppliers (Sigma-Aldrich and STREM) and used without further purification. Manipulations were carried out under inert conditions using Schlenk-line and glove-box techniques (O 2, H 2 O, below 1 ppm). Solvents were purified, dried and saturated with Ar using an automatic catalytic Solvent Purification System (MBraun, Garching). Elemental Analyses were performed in the Microanalytical Laboratory of the Department of Analytical Chemistry at the Ruhr-University Bochum. For metal determination (Zn, Ga) an AAS apparatus by Vario of type 6 (1998) was employed, C, H, N - analyses were carried out using a Vario CHNSO EL (1998) instrument. Infrared spectra were recorded inside a glove-box on a bruker Alpha-P FT- IR instrument in the ATR geometry with a diamond ATR unit. 1 H, 2 H, and 13 C-CP-MAS- NMR-spectra were measured with a Bruker DSX, 400 MHz spectrometer under MAS conditions in 2.5 mm ZrO 2 rotors with a sample volume of 12 µl. The rotation frequency was 1

2 20 khz. All spectra were measured applying pulse programs written by H.-J. Hauswald at the Department of Analytical Chemistry of the Ruhr-University Bochum. For the proton and deuterium MAS-NMR measurements a ZG4PM pulse program was used. The carbon NMR measurements were carried out with the pulse program CP4C (cross polarization) and were referenced to adamantine at ppm. Powder XRD (PXRD) measurements of the samples were recorded on a D8-Advance Bruker AXS diffractometer with Cu K α -radiation (λ = Å) and a focused Göbel mirror in θ - 2θ geometry with a position sensitive detector in a 2θ range from 5 90 at a scan speed of 10 s / step. The experimental set-up was in capillary mode. For data accumulation, the samples were filled under inert gas (glove-box) into 0.7 mm capillaries which were then sealed. N 2 sorption measurements were performed using a Quantachrome Autosorp-1 MP instrument and optimized protocols. Thermo gravimetric analyses (TGA) were performed on a Seiko TG/DTA 6300S11 instrument (sample weight approximately 10 mg) at a heating rate of 5 K min 1 in a temperature range from 303 K 1273 K. The measurement was performed at atmospheric pressure under flowing dinitrogen ( %; flow rate = 300 ml min 1 ). Photoluminescence (PL) experimental setup: the sample was excited at 300 nm (4.13 ev) by a modulated (lock-in-technique) 30 W deuterium lamp combined with a band pass filter at room temperature. The resulting photoluminescence was collected by a quartz lens dispersed through a monochromator (spectral resolution of 1 nm) and registered by means of a photomultiplier (Hamamatsu R 375 P). Transmission electron microscopic measurements were carried out at the EMAT laboratory of the University of Antwerp, Belgium. ADF-STEM and spatially resolved STEM-EELS experiments were carried out on a FEI Titan cubed microscope fitted with an aberration-corrector for the probe forming lens and a GIF Quantum spectrometer, operated at 120kV with low electron dose to minimize possible beam damage to the nanoparticle supported framework. The STEM convergence semi-angle used was ~18.5mrad, the ADF 2

3 collection semi-angle β was ~ 30 mrad for the ADF images in Figure 2, the ADF and EELS collection semi-angle β mrad was ~ 60 mrad for the images in Figure 3. The EELS data was acquired by scanning the electron probe over the sample and acquiring an EELS spectrum at each point of a 90*89 pixel spectrum image. After acquisition, the EELS data was treated using principle component analysis (PCA) to minimise the effect of random noise. Maps were generated by integrating the EELS signals over an appropriate energy window after powerlaw background removal. BFTEM images were acquired on a Philips CM30 equipped with a field-emission gun operated at 300 kv. Synthesis and further analytical methods ZIF-8. The ZIF-8 material was purchased from Sigma-Aldrich and activated at 573 K in dynamic vacuum (10-3 mbar) for 24 h. N 2 sorption measurements (BET model) reveal a surface area of 1918 m 2 g -1. Trimethylamine gallane. Synthesis of the volatile precursor followed the procedure described by Shriver et al. (Inorg. Synth. 1977, 17, 42) Therefore, 2.7 g (15.3 mmol) GaCl 3 were dissolved in 10 ml diethylether and cooled to 196 K before 1.95 g (245.3 mmol) LiH (dissolved in 45 ml Et 2 O) were added and slowly warmed (6 h) to room temperature. Filtration of this suspension leads to a colorless solution, which was again cooled to 196 K g (14.0 mmol) (CH 3 ) 3 NHCl were carefully added to the solution, resulting in the loss of dihydrogen (gas evolution). The reaction was kept at 253 K for 6h and again filtrated. The solvent was removed under vacuum (10-3 mbar) at 243 K, leading to the formation of a bright white precipitate with a yield of 89 % (1.8 g). Elemental analysis (wt.-%): calculated: C, 27.3; H, 9.2; N, 10.6; Ga, 52.8; found: C, 28.1; H, 8.9; N, 10.2; Ga, H-NMR (ppm): 1.82 (H 3 C) 3 GaH 3 ; 4.96 (H 3 C) 3 GaH C-NMR (ppm): (H 3 C) 3 GaH 3. 3

4 Chemical vapor infiltration. Typical amounts of 200 mg activated ZIF material were placed together with the selected amount of trimethylamin gallane [(CH 3 ) 3 NGaH 3 ], both contained in small glass vials, in a glass tube under Ar atmosphere. The tube was evacuated to 10-5 mbar and cooled to 273 K. During the loading procedure a visible reduction of the precursor amount can be observed. After 7 days the tube was opened under inert gas conditions and the material was transferred in a glass vessel and stored under Ar atmosphere at 243 K. Elemental analysis (wt.-%): found: C, 39.1; H, 5.7; N, 21.3; Zn, 22.6; Ga, Cyclotrigallazane@ZIF mg of [(CH 3 ) 3 NGaH 3 ]@ZIF-8 were filled in an autoclave under inert gas conditions. After a short evacuation period 1 bar gaseous ammonia (d 3 - ammonia) were introduced to the autoclave and the system was heated to 323 K. After a reaction time of 48 h dynamic vacuum (10-3 mbar) was applied to get rid of excess ammonia (d 3 -ammonia) and further by-products. The white powder was transferred in a glass vessel and stored under Ar atmosphere at room temperature. Elemental analysis (wt.-%): found: C, 35.2; H, 4.3; N, 23.7; Zn, 22.6; Ga, GaN@ZIF mg of (H 2 GaNH 2 ) were filled in an autoclave under inert gas conditions and shortly evacuated. 3 bar gaseous ammonia were applied and the system was heated up to 423 K for 24h. Subsequently, thermal annealing under dynamic vacuum (473 K, 10-3 mbar) was performed for additional 24 h, resulting in the final formation of GaN@ZIF-8. Elemental analysis (wt.-%): found: C, 35.9; H, 3.9; N, 23.7; Zn, 24.8; Ga, N 2 sorption measurements (BET model) reveal a surface area of 1055 m 2 g -1. 4

5 Figure S1. Thermo gravimetric analyses (TGA) of (black), (H 2 GaNH 2 ) 3 /NMe (blue), and [(CH 3 ) 3 NGaH 3 ]@ZIF-8 (red) show a thermal stability of the composite materials up to 773 K. [(CH 3 ) 3 NGaH 3 ]@ZIF-8 reveals a weight loss of 12 wt.%, which is in good agreement with the elemental analysis. The TGA curve of (H 2 GaNH 2 ) 3 /NMe shows only a weight loss of 2.5 %, indicating the release of residual NMe 3 as a by-product. 5

6 Figure S2. 1 H-MAS NMR spectra of [(CH 3 ) 3 NGaH 3 ]@ZIF-8 (a), (H 2 GaNH 2 ) (b), GaN@ZIF-8 (c), and activated ZIF-8 (d). 6

7 Figure S3. 13 C-CP-MAS NMR spectra of activated ZIF-8 (a), [(CH 3 ) 3 NGaH 3 ]@ZIF-8 (b), (H 2 GaNH 2 ) (c), and GaN@ZIF-8 (d). A signal at 48.4 ppm is visible in (b), corresponding to the methyl groups of [(CH 3 ) 3 NGaH 3 ]@ZIF-8. 7

8 Figure S4. Powder x-ray diffraction patterns of activated ZIF-8 (a), [(CH 3 ) 3 NGaH 3 ]@ZIF-8 (b), (H 2 GaNH 2 ) (c), GaN@ZIF-8 (d), and a physical mixture of GaN powder (13 wt.%) with activated ZIF-8 (e). A decrease in intensity of the first ZIF-8 reflection (110) of the PXRD pattern of [(CH 3 ) 3 NGaH 3 ]@ZIF-8 and (H 2 GaNH 2 ) is present, giving hint for pore filling. The absence of GaN reflections in (d) seems to result from a concentration effect, since the PXRD pattern of a physical mixture of hexagonal GaN bulk powder with ZIF-8 looks similar to that of GaN@ZIF-8. 8

9 Figure S5. The 2 H-MAS NMR spectrum of (H 2 GaND 2 ) shows two nearby signals, which can be assigned to the deuterated amido groups of the embedded trimer. Figure S6. 1 H-MAS NMR spectrum of (H 2 GaNH 2 ) (a) and (H 2 GaND 2 ) (b). 9

10 Figure S7. FT-IR spectra of (H 2 GaNH 2 ) (black) and (H 2 GaND 2 ) (red). Two weak absorption bands in the region of cm -1 are observable in the spectrum of (H 2 GaND 2 ) indicating ND 2 strechting vibrations. 10

11 h = J s Planck's constant m n = 0.27 m 0 m p = 0.8 m 0 m 0 = kg effective mass of electrons in GaN effective mass of holes in GaN rest mass of the electron Figure S8. Calculation of the average GaN particle diameter was performed using this equation. It correlates the absolute value of the energy shift E, derived from the PL spectrum with quantum dot size a. Figure S9. Bright-field TEM image of GaN@ZIF-8 showing speckled contrast in medium magnification, indicating the presence of nanoparticles. 11