Enabling Broadband Solar‐Blind UV Photodetection by a Rare‐Earth Doped Oxyfluoride Transparent Glass‐Ceramic

Abstract Oxyfluoride transparent glass‐ceramics (GC) are widely used as the matrix for rare‐earth (RE) ions due to their unique properties such as low phonon energy, high transmittance, and high solubility for RE ions. Tb3+ doped oxyfluoride glasses exhibit a large absorption cross section for ultraviolet (UV) excitation, high stability, high photoluminescence quantum efficiency, and sensitive spectral conversion characteristics, making them promising candidate materials for use as the spectral converter in UV photodetectors. Herein, a Tb3+ doped oxyfluoride GC is developed by using the melt‐quenching method, and the microstructure and optical properties of the GC sample are carefully investigated. By combining with a Si‐based photo‐resistor,a solar‐blind UV detector is fabricated, which exhibits a significant photoelectric response with a broad detection range from 188 to 400 nm. The results indicate that the designed UV photodetector is of great significance for the development of solar‐blind UV detectors.

Actually, the incorporation of RE into crystal structures was uncontrollable in the traditional oxyfluoride GCs due to the due to a severe mismatch of ionic radius between RE ions and substitutable ions.A large number of fluoride crystals without the activator ions are precipitated.In our GCs, the crystallization of KTb2F7 is completely governed by a small number of the doped RE ions and RE ion is a part of the crystal.Tb 3+ ions were spontaneously incorporated into fluoride crystals during the crystallization process of GCs.The quantity of crystals in GC is small and the incorporation of RE into crystal structures is controllable.However, the quantum yield vualue in Tb 3+ doped NaYF4 GC is 40.20%.These results indicate that our designed GC is a more efficient material for the emission of Tb 3+ .

Fig. S10 Transmission spectra of GCs containing various concentration of Tb 3+ ,
the inset is photos of the corresponding GC samples.As presented in Fig. S1, the diffraction peaks of Tb 3+ doped GCs are broader than those in no-doped GC, indicating that the crystal sizes in Tb 3+ doped GCs are smaller than in no-doped GC.As a result, the transmittance of Tb 3+ doped GCs are all higher than that of the non-doped GC.

Fig. S11
Transmission spectra of our KTb2F7 GC and Tb 3+ doped NaYF4 GC, the inset is the photos of the GCs (left: KTb2F7 GC, right: NaYF4 GC).The KTb2F7 GC possesses high tranmittance in visible region, which is much higher than the Tb 3+ doped NaYF4 GC.In the traditional NaYF4 GC, a large number of crystals are precipitated in the GC, leading to severe scattering and low transmittance.The NaYF4 GC is almost opaque.Therefore, our designed GC is more tranparent than the traditional NaYF4 GC.

Fig
Fig. S1 XRD patterns of xTb 3+ doped glass and GCs, and and JCPDS Cards No: 85-1382 (K2SiF6) and 32-0849 (KTb2F7).No crystal is precipitated in the as-quenched glass.After heat-treatment, only K2SiF6 crystals are precipitated in the no-doped GC.The crystal phase turns to KTb2F7 by the doping of 0.5% Tb 3+ and the diffraction peaks increase monotonously when the doping concentration is increased from 0.5 to 6.0%.

Fig. S2
Fig. S2 Schematic diagram of crystallization mechanism for traditional GCs and our GCs.In the traditional oxy-fluoride GCs, a large number of Ln(Ln=Y, Lu, Gd, La)F3 were added into the glass to precipitate fluoride crystals like NaLn(Ln=Y, Lu, Gd)F4, LaF3 and YF3.Then rare earth (RE) activators were expected to enter these fluoride crystal structures via cationic substitution for Y 3+ , Lu 3+ , Gd 3+ or La 3+ ions.

Fig. S3
Fig. S3 Raman spectra of GCs doped with different concentration of Tb 3+ .The intensity of the band peaking at 349 cm -1 increases with the increase of Tb 3+ concentration, implying the growth in the fraction of the precipitated KTb2F7 crystals.

Fig
Fig. S4 Decay curves of Tb 3+ emission at 544 nm of glass and GC heat treated at 540 o C for 10h.Excited by 371 nm light, the emission lifetime of glass monitored at

Fig
Fig. S5 Emission spectra of 5.0Tb 3+ doped GCs fabricated by heat treatment at 540 o C for different durations.Under excitation at 371 nm, intense emissions peaks around 544 nm are observed in the spectra of GCs.The emission intensity rises as the heat treatment duration increases from 5 h to 10 h because of the increase in the number and volume of KTb2F7 crystals precipitated.By further increasing the heat treatment duration to 11 and 13 h, the emission intensity decreases possibly due to enhanced inter-particle coupling that leads to quenching.

Fig. S6
Fig. S6 Emission spectra of 5.0Tb 3+ doped GCs fabricated by heat treatment at various temperatures.The emissions of GC heat treated at 530 o C is weak, which is ascribed to the low concentration of crystals in the sample.By rising the heat treatment temperature to 540 o C, more crystals are precipitated in the GC and the emission intensity of Tb 3+ increases notably.However, for the GC heat treated at 550 o C, too many crystals are precipitated from the glass, which could lead to the decrease of emission caused by enhanced inter-particle coupling.

Fig. S7
Fig. S7 Transmisson spectra of glass and GCs heat treated at different temperatures.The GC heat treated at 540 o C exhibit high transmittance (~90% at 544 nm).However, the tranmittance decreases obviously and the scattering becomes severe when the heat treated temperature rises to 550 o C due to the enlargement of crystal size.

Fig. S8
Fig. S8 Emission spectra of KTb2F7 GC and Tb 3+ doped NaYF4 GC.Under excitation at 371 nm, emissions of Tb 3+ are observed in the spectra of GCs.The emission intensity of KTb2F7 GC is stronger than that of NaYF4 GC due to the comtrollable incorporation of Tb 3+ into fluoride crystals.