作为可见光通信的颜色转换器的钙钛矿纳米晶体

Visible light communication (VLC) is an emerging technology that uses light-emitting diodes (LEDs) or laser diodes for simultaneous illumination and data communication. This technology is envisioned to be a major part of the solution to the current bottlenecks in data and wireless communication. However, the conventional lighting phosphors that are typically integrated with LEDs have limited modulation bandwidth and thus cannot provide the bandwidth required to realize the potential of VLC. In this work, we present a promising light converter for VLC by designing solution-processed CsPbBr3 perovskite nanocrystals (NCs) with a conventional red phosphor. The fabricated CsPbBr3 NC phosphor-based white light converter exhibits an unprecedented modulation bandwidth of 491 MHz, which is ∼40 times greater than that of conventional phosphors, and the capability to transmit a high data rate of up to 2 Gbit/s. Moreover, this perovskiteenhanced white light source combines ultrafast response characteristics with a high color rendering index of 89 and a correlated color temperature of 3236 K, thereby enabling dual VLC and solid-state lighting functionalities.

We synthesized CsPbBr3 perovskite NCs via a modifified hotinjection method similar to that presented in previous work28 (see the Experimental Methods). The NCs were characterized by high-resolution transmission electron microscopy (HRTEM) (Figures S1), which revealed uniform cubic-shaped NCs with an average size of 8.3 ± 0.8 nm. The X-ray diffffraction (XRD) pattern of the NCs exhibited the cubic CsPbBr3 phase (see Figure S2). The inset in Figure 1a shows the absorption and photoluminescence (PL) spectra of the NCs dispersed in toluene. As can be seen, the absorption spectrum of the CsPbBr3 NCs does not exhibit any spectral features at wavelengths longer than 520 nm, which is consistent with previous reports The NCs exhibit a sharp PL emission peak at 512 nm with a narrow full width at half-maximum (fwhm) of 22 nm.

Time-resolved laser spectroscopy has proven to be a critical part of studying excited-state dynamics.31−33 Here, to study the carrier dynamics of these CsPbBr3 NCs, we performed femtonanosecond transient absorption (fs-ns-TA) experiments (experimental setup detailed elsewhere34,35) and time-resolved PL measurements, and the results are presented in Figure 1. The ns-TA measurement was recorded following laser pulse excitation at 350 nm with a pump flfluence of 9 μJ/cm2 . In this TA experiment, we followed the ground-state bleach (GSB) recovery to monitor the charge recombination dynamics, as shown in Figure 1a. The GSB observed at approximately 505 nm, which corresponds to the steady-state absorption spectrum, reveals a full recovery in a 30 ns time window with a time constant of 6.4 ns (shown in Figure 1b). Because of the low pump intensity for photoexcitation, Auger recombination due to carrier multiplication generated by multiphoton absorption is not appreciable.36 To also confifirm that a multiple exciton generation process is not dominant in the observed dynamics, we performed the TA experiments at two difffferent pump flfluences (9 and 18 μJ/cm2 ), and almost identical kinetics are recorded as shown in Figure 1b.

Additionally, we have performed the fs-TA of CsPbBr3 NCs, and the results are shown in Figure 1c. The GSB recovery shows an additional component with a characteristic time constant of 103 ± 40 ps, which may be attributed to nonradiation recombination due to surface traps.37,38 To further understand the carrier dynamics and the radiative recombination process, we measured the PL lifetime via timecorrelated single-photon counting (TCSPC) using a flfluorescence up-conversion spectrometer with excitation at 400 nm (Figure 1d). The PL lifetime decay profifile was collected at 515 nm. The decay curve can be fifitted with a single-exponential function with a lifetime of approximately 7.0 ± 0.3 ns. It is worth pointing out that the PL decay of CsPbBr3 NCs with two difffferent excitation flfluencies shows a similar decay trend (see Figure 1d), which is consistent with TA data. This short lifetime of about 7 ns is comparable with the reported values for similar sized CsPbBr3 NCs.21,39,40 We have also observed a similar kinetics trend from both solution and fifilm samples of CsPbBr3 NCs in time-resolved experiments shown in Figure S3. Because of their high PLQY of ∼70% and short radiative recombination lifetime of 7.0 ± 0.3 ns, CsPbBr3 NCs are promising materials for generating VLC and SSL.

To study the white light generated by utilizing CsPbBr3 NCs as light converters for SSL, a mixture of a green-emitting CsPbBr3 NC phosphor with a red-emitting nitride phosphor (LAM-R-6237, Dalian Luming Group) (CsPbBr3 NCs are drop-casted onto a red-emitting phosphor to form a fifilm) is excited by a GaN blue-emitting LD (λ = 450 nm) (see Figure 2a inset). Operating at 200 mA, the LD generates a warm white light (CCT = 3236 K) with a CRI value of 89, as calculated after its emission passes through the phosphor mixture. Compared with the warm white LED bulbs available on the market, which have a typical CRI of 70−80, the white light generated herein achieves higher quality emission that is suitable for lighting. Figure 2a,b show the spectrum and the chromaticity diagram (CIE 1931) coordinates (0.3823, 0.3079) of the generated white light. The CRI value of the CsPbBr3 NCs with a red-emitting phosphor is also greater than the reported value of 76 for organic down-converted white VLC transmitters.10 Our device also shows enhanced performance over commercial WLEDs based on a YAG:Ce3+ phosphor, which exhibits a relatively low CRI (<75) and high CCT (>7765 K). The device using a perovskite NC phosphor as demonstrated in this work suggests a better quality of white light. In comparison, our results present a higher CRI of 89 and a lower CCT of 3236 K, which are essential factors for indoor illumination42 and optical display applications.

Fig1

The crude solution was cooled with an ice−water bath and transferred to centrifuge tubes directly. After centrifuging at 8000 rpm for 15 min, supernatant was discarded and the precipitate was collected separately. The precipitate was dispersed in toluene for centrifugation at 7000 rpm for 5 min, the supernatant was removed, and the new precipitate was collect for another centrifugation by dispersing in toluene. Then the shiny green solution was collected for further experiment.