The infrared emitter is an important photoelectric component for various applications such as wireless communication, multispectral imaging systems, and biomedical sensing technology [1–4]. It is mainly covering the short-wave infrared (0.75–3 μm), mid-wave infrared (3.0–6.0 μm), and long-wave infrared (6.0–15.0 μm) wavelength ranges, which have some significant advantages of strong diffraction ability, anti-electromagnetic interference, high concealment performance, and so on. Light emitting diodes (LEDs) and MEMS thermal radiation sources have been widely studied because of their significant advantages and mature research technology [5–7].

The infrared emitting diode (IR LED) was fabricated by using gallium arsenide (GaAs) and gallium aluminide (GaAlAs) [8,9]. The IR LED could directly convert electrical energy into infrared optical signals for further applications. Generally, these infrared emitters have some remarkable characteristics of small size, low operating voltage, fast response, and long service life. Tseng et al. and Tillement et al. designed and fabricated a GaSb/GaAs quantum dot heterojunction infrared diode. The interface carrier aggregation can be realized based on the GaSb/GaAs electron/hole confinement effect, and NIR signals with central peaks of 1142, 1133, and 1125 nm were emitted stably in room temperature condition [10,11]. With the introduction of quantum dots, perovskite, and fluorescent powder, researchers have also developed a series of high-performance infrared LEDs. Lim et al. have synthesized near-infrared emitting ${\text{CuInS}}_2/\mathrm{ZnS}$ quantum dots using binary sulfur precursors composed of 1-dodecyl mertan (DDT) and HMDS, and the resulting quantum dots exhibit 65% high photoluminescence quantum efficiency (PLQE) at a long emission wavelength of 920 nm [12]. To acquire mid-infrared signals, Granger et al. constructed an OP-GaAs waveguide architecture based on orientation patterned gallium arsenide. By using its nonlinear response and wide transparent window, mid-infrared frequency reduction was realized with the help of an integrated ultra-fast fiber pump source. Its wavelength can be continuously tuned from 4 to 9 μm excited by 2750 nm pulse laser [9]. As a kind of typical infrared emitters, most of them focus on the near-infrared frequency range. Higher emitting power and longer transmission distance have also been studied by researchers in recent years.

Compared with IR LEDs, the thermal infrared MEMS irradiation source could emit mid-/far-infrared signals driven by external bias voltage. Müller et al. proposed high-emission silicon-based micro-hot plate to produce a hemispheric spectral absorbance of 0.97 μm in the wavelength range [13]. The device shows 2.6 times higher infrared emission intensity compared to uncoated silicon-based emitters. Li et al. designed $\mathrm{Al}/{\mathrm{SiO}}_2/\mathrm{Si}$ hexagonal perforated microarrays and used silicon wafers on insulators to produce hexagonal photonic crystal infrared emitters by using MEMS technology [14]. The MEMS-based plasmon infrared emitters can generate middle and far uniform infrared emission signals at 10 V bias voltage. Wang et al. simulated the thermal radiation characteristics of silicon carbide (SiC) microstructures. By optimizing the structural parameters, the thermal emission/absorption spectrum and direction control can be effectively achieved [15]. In the same year, Asano et al. fabricated a resonant heat emitter in the near-infrared ($\sim 1.5\mathrm{\mu m}$) wavelength range. The results demonstrated that by controlling the doping concentration in silicon and the resonance enhanced absorption, accurate control of the material absorption coefficient can be achieved. Thus, the thermal infrared emission peak of the photon structure can be modulated without adding additional absorption properties of the material [16].

In the field of carbon-based infrared radiation, graphene has excellent carrier mobility and thermal stability, which provide a novel approach to develop an infrared emitter source. Lots of attention was focused on carbon-based materials and the infrared emitter [17,18]. Freitag et al. fabricated graphene back-gated transistors to explore thermal radiation behavior. An $(1.6\pm 0.8)\%$ emissivity value was extracted in the near-infrared frequency range based on Planck’s law [19]. Chae et al. exhibited the joule heat formation process such as electron–phonon interaction, the phonon decay mechanism, and lattice temperature change. And the strong scattering effect between phonons and phonons was the dominant factor for acquiring a wide infrared emission spectrum [20]. In practical applications, graphene was commonly integrated on various substrates such as Si-based substrate. However, the carrier transport and phonon scattering effect are sensitive to the disturbances of the surface or edge state when graphene is attached on the surface of the substrate. For this reason, Dorgan et al. constructed the graphene suspension structure by attaching graphene microstrips to metal electrodes. By eliminating the influence of the substrate, the highest radiation temperature exceeded 2500 K because of the enhancing mechanism of the optical resonator [21]. Besides that, exploring the appropriate substrate is also an effective method. Gao et al. integrated wafer-level graphene emitter arrays on the silicon substrate, and the graphene emitting unit exhibited temperature change modulation range (300–800 K). Its energy emission intensity was increased linearly with the external control electrical field values. The results are expected to meet the requirements of large area integration and high-performance infrared emitting devices [22]. It is important to understand the graphene-based infrared emitting principle and explore the high-performance infrared source for further applications. In this paper, we adopted PZT polarized substrate to support and protect graphene crystal. Higher carrier mobility, [$\mathrm{11,361.55}{\mathrm{cm}}^2/(\mathrm{V}\cdot \mathrm{s})$] can be acquired because of polarized substrate for enhancing the electron–phonon coupling effect. A slight Raman redshift was observed as the external bias voltage varied from 3 to 15 V, indicating an increase in temperature and an elongation of the C–C bond length. Its infrared emitting efficiency reached 0.7 and 0.758 at 1.0–3.8 and 8–14 μm wavelength. The temperatures of graphene/PZT heterostructure can be tuned by external bias voltage with good linearity, in which $\sim 180.3°\mathrm{C}$ can be acquired at 11 V bias voltage in the process. During the voltage-application process, pulses were applied to the graphene/PZT structure periodically at intervals of approximately 5 s. The heterostructure exhibited a 1.5 s rise time and a 1.08 s fall time in the temperature change between 26°C and 172°C. This pulse test process was continued for 2000 cycles without any attenuation. Besides that, the infrared images could be clearly observed at $3\mathrm{mm}\times 3\mathrm{mm}@20\mathrm{m}$. Combining with multiple display units, alphabetic information could be transmitted in the infrared frequency band. All these parameters could provide support for the infrared emitting source and optical communications.

The infrared emitter contains graphene and ferroelectric PZT substrate. The PZT film with 100 nm thickness was first prepared on the 50 μm mica substrate based on the sol-gel method. The single-layer graphene used here was purchased from SixCarbon Technology Shenzhen (China). The wet process was adopted to transfer CVD graphene from copper substrate to PZT substrate. In the process, copper sulfate solution was used for copper substrate, deionized water was used for impurity ions, and acetone solution was used to remove the surface photoresist of graphene. When CVD graphene was attached to PZT substrate, the sample was placed in a vacuum drying oven to remove residual solution for better interface contact.

Electrical curves including the $I\text{-}V$, cyclic performance test, and pulse voltage were obtained by the 2611B instrument. The graphene/PZT sample was attached to the electrical base surface, and a probe station was subsequently fixed with electrical base for further testing by the PPMS-9 instrument. Some important parameters including carrier density, resistivity, and mobility could be directly exported through matching software based on the following formulas: $n=1/R_{H}e$ ($R_H$ is the Hall coefficient) and $\text{μ }=1/n\rho e$ ($n$ is the carrier density, $\rho$ is the electrical resistivity, and $\mu$ is the carrier mobility). The relevant data were completed by the sci-go instrument testing platform. Raman data of the sample at different bias voltages were obtained by the in situ testing method; i.e., Raman spectra excited by the 532 nm laser were collected at a center location in real time when external bias voltages were applied to both sides.

The infrared test contains infrared efficiency and infrared image display contents. For the infrared efficiency test, 2602B instrument and infrared emissivity equipment were used to test the device properties of the sample in the near-mid infrared frequency band. The test system mainly consists of three parts: the power supply system, vacuum cold environment system, and control measurement system. In the test process, the sample was placed in a vacuum blackbody radiation chamber, and the data were results from the ratio of the spectral emissivity of the sample to the spectral emissivity of the reference black body with the same temperature based on ${\epsilon }_{\lambda }(T)=M_{\lambda }(T)/M_{h\lambda }(T)$. [$M_{\lambda }(T)$ is the spectral radiative exitance of the sample, $M_{h\lambda }(T)$ is the spectral emissivity of the reference blackbody, and ${\epsilon }_{\lambda }(T)$ is the spectral emissivity of the sample.] For infrared image display, Keithley 2602 instrument and FLIR T540 infrared camera were used to tune and observe the infrared image of graphene/PZT heterostructure unit. Accurate temperature and current changes could be read directly from the matching software.

Graphene has extremely high carrier mobility and in-plane phonon transport efficiency. When external bias voltage was applied on graphene crystal, its electrons in non-equilibrium state could cause the heating and acceleration behavior at bias voltage [Fig. 1(a)]. The carrier transport behavior and electron–phonon inelastic scattering mechanism can be explained by the Boltzmann equilibrium equation [22–24]. The corresponding was expressed as follows: $$U_{k^{\prime }k}^{ac}=\int {\mathrm{d}}^{2}r{\psi }_{k^{\prime }}^{*}(r)V_s(r){\psi }_k(r),$$in which $V_s(r)$ is the scattering potential of electrons and acoustic phonons, $s$ represents the different acoustic modes (including the longitudinal acoustic mode and transverse acoustic mode), and ${\psi }_k(r)$ is the electron wave function in graphene. The electron–phonon scattering effect requires conservation of energy and momentum, and its derivation formula is as follows: $$k^{\prime }+k-\left(\frac{V_s}{V_F}\right)q_x=0$$in which $k^{\prime }$ and $k$ are the wave vectors of the electron before and after scattering. $V_s$ and $V_F$ are the Fermi velocity of the electron and acoustic phonon velocity, and $q_x$ is the phonon wave vector. In formula of $k^{\prime }+k-(V_s/V_F)q_x\ge k-(V_s/V_F)q_x=G$, $V_s$ is much less than $V_F$; then $k$ is much less than $q_x$ and leads to $G=(1-V_s/V_F)q_x>0$. As a result of that, inter-band absorption could not occur in the electron–phonon scattering process [Fig. 1(b)]. From the point of view of energy matching, multiple electron–phonon coupling processes will promote electrons to jump to the higher energy band. Subsequently, infrared signals could be produced when electrons fall back from excited state to stable state through intra-band and inter-band irradiation, which is the main reason for producing near-infrared irradiation signals [25]. On the other hand, phonon oscillation also could be induced by the rapid movement of electrons in graphene film under external bias voltage, in which infrared signals also could be emitted. Researchers find that non-equilibrium phonon vibration has played an important role in mid-/far-infrared irradiation [26,27]. Higher sound velocity is useful for fast response infrared emitting because of lighter carbon atom and C–C strong chemical bond. And graphene was commonly integrated on the surface of the substrate for various applications. The interface between graphene and substrate significantly hinders the phonon transport efficiency [28,29]. PZT is a typical ferroelectric film with surface electrostatic field, which can be used to modulate the Fermi level and increase the carrier concentration of graphene crystal. Together with surface charge injection, the electron–phonon interaction could be further enhanced to promote infrared emission.

Ferroelectric materials with spontaneous polarization have been usually used to tune the electronic structure and carrier density of 2D film integrated on its surface [30–32]. As a typical ferroelectric material, PZT could produce obvious surface potential for enhancing the interaction force between ferroelectric substrate and graphene film based on the intrinsic polarized electric field for inhibiting interface phonon scattering, which leads to higher efficiency of energy transport in graphene crystals. Besides that, the Fermi level may also be tuned by the surface electric potential of PZT film for increasing the electrons’ concentration. Larger current could be acquired at the lower bias voltage, and stronger interaction between electrons and phonons leads to brighter infrared emitting light. Combining with ultra-low thermal conductivity of PZT preventing the loss of graphene heat, the graphene/PZT heterostructure was finally proposed to construct a high-performance infrared emitting source. A series of heterostructure characterization and analysis was provided as follows. Figure 1(c) is a schematic of the graphene/PZT infrared emitting structure. The gap distance of graphene covered by two metal electrodes is $\sim 3\mathrm{mm}$. Compared to some other graphene-based infrared emission devices, the device presented in the paper presented larger size and emitting area and reliable fabrication process based on the impressive structure and emitting theory.

Figure 2(a) shows the SEM images of the graphene/PZT heterostructure sample. Graphene was flat attached to the surface of the PZT substrate. Smooth graphene film and minor fold can ensure better contact and larger interface interaction force including van der Waals force and electrostatic field force. And flat contact interface also can form a uniform electron distribution or stable phonon vibration for stable and durable infrared irradiation performance. The reason for wrinkles and irregularities is probably the non-equilibrium force or self-deformation in the external environment, which is important for carrier transport in graphene crystal. The optical performance is closely related to carrier transport behavior and electron–phonon coupling interactions. Some irregularities such as wrinkles or impurities are easier to cause local accumulation of carriers and high energy concentration at external bias voltage, which lead to the structure being burned out and scrapped. Because PZT film was prepared on the surface of mica film substrate, the I-V curves and carrier mobility of graphene on PZT and mica substrates were tested and are exhibited in Figs. 2(b) and 2(c). It is obvious that the graphene on PZT substrate presented larger current values than the graphene/mica structure. Higher current and lower resistivity can be acquired for the graphene/PZT sample. The Hall coefficient ($R_H$) and electrical resistivity ($\rho$) of the sample can be directly measured by PPMS-9 equipment. The carrier densities of graphene/mica and graphene/PZT were $\sim 8.57\times {10}^{18}{\mathrm{cm}}^{-3}$ and $2.82\times {10}^{18}{\mathrm{cm}}^{-3}$ based on the formula of $n=1/(R_H\times e)$. ($n$ is the carrier density, $R_H$ is the Hall coefficient, and $e$ is the elementary charge.) Its carrier mobility of graphene/mica and graphene/PZT samples was $2736.07{\mathrm{cm}}^2/(\mathrm{V}\cdot \mathrm{s})$ and $\mathrm{11,361.55}{\mathrm{cm}}^2/(\mathrm{V}\cdot \mathrm{s})$ based on the formula of $\mu =1/(n\times \rho \times e)$. ($\rho$ is the electrical resistivity.)

The results show a significant modulation effect of PZT polarized substrate on graphene film. Larger current and higher carrier mobility could induce more phonons due to strong scattering between electrons and phonons. The interaction between phonons and electrons in the graphene crystal induces electrons into an excited state upon receiving external energy, while phonon scattering generates higher temperatures, enabling thermal infrared irradiation. Consequently, the heterostructure may exhibit higher efficiency in infrared emission intensity.

Higher temperature or electron–phonon interaction will influence the chemical bonding vibration of molecules, which can be characterized by Raman spectra for further analysis. Meanwhile, thermal conductivity of graphene film is the sum of contributions of all phonon modes. By detecting the anharmonic properties of individual optical phonon modes through Raman spectrum signals (frequency shift or linewidth), the heat irradiation mechanism of graphene crystal can be revealed. In Fig. 2(d), the positions of the G peak are $1572.1{\mathrm{cm}}^{-1}$, $1571.8{\mathrm{cm}}^{-1}$, $1571.2{\mathrm{cm}}^{-1}$, and $1569.3{\mathrm{cm}}^{-1}$ at 3 V, 5 V, 10 V, and 15 V bias voltage, respectively. The positions of the 2D peak are $2682.4{\mathrm{cm}}^{-1}$, $2681.2{\mathrm{cm}}^{-1}$, $2680.1{\mathrm{cm}}^{-1}$, and $2679.3{\mathrm{cm}}^{-1}$ at 3 V, 5 V, 10 V, and 15 V bias voltage, respectively. Then a slight redshift is produced at the G peak ($\mathrm{\Delta }f\approx 2.8{\mathrm{cm}}^{-1}$) and the 2D peak ($\mathrm{\Delta }f\approx 3.1{\mathrm{cm}}^{-1}$) when higher external bias voltage is applied. The phenomenon may result from the longer C–C chemical bond and stronger electron–phonon interaction under higher temperature condition [33,34].

Figures 3(a) and 3(b) show the emission spectra in the near-infrared (1–3 μm) and mid-infrared (7–25 μm) ranges. Due to PZT being prepared on the surface of mica substrate, the infrared emitting efficiency of graphene/mica was characterized as the reference sample. In the near-infrared frequency band, its maximum emitting efficiency increased from 0.6 to 0.7. For the PZT/graphene heterostructure, higher electron density led to stronger electron–phonon interaction. When electrons get energy from inelastic scattering with multiphonons, they will transition to higher energy levels. Near-infrared photons will be emitted with the interband transition of electrons. It should be noticed that a single phonon could not excite interband transition of electrons limited by own energy values. It is important to construct a polarized heterostructure to enhance the electron–phonon coupling mechanism. For mid-far-infrared signals, its photon resulted from the phonon vibration model. In Fig. 3(b), the infrared emitting efficiency has an obvious increasing trend from 0.103 to 0.65 with the bias voltage increasing from 3 to 11 V. The increasing trend resulted from high speed/energy electrons in greater electric field intensity, which led to stronger interaction between electrons and phonons. The maximum electric field intensity was $\sim 37\text{V/}\mathrm{cm}$ at 11 V bias voltage. And the value is lower than 800 V/cm for nonlinear saturation state [35]. Electronically controlled infrared emitting efficiency is an effective way, and Figs. 3(c) and 3(d) provide a relative electro-optical conversion test. When the excited voltage varied from 5 to 11 V, its optical power density was also varied from 0.22 to $2.72\mathrm{mW}/{\mathrm{cm}}^2$, which is directly measured by optical power equipment. Electrical output power and infrared radiant power were also exhibited in Fig. 3(d); its maximum electro-optical conversion value is $\sim 6.2\times {10}^{-2}$ under 8 V excited voltage (electrical power: 15.84 mW; infrared radiant power: 0.98 mW). The electro-optical conversion value will increase in the initial voltage stage. However, the optical power presented an upward trend with the increase of external excited voltage. Its corresponding electro-optical conversion value tended to a saturation infrared radiant power in the $\sim 5.6\times {10}^{-2}$ to $\sim 6.2\times {10}^{-2}$ range.

For exhibiting the emission intensity in the 7–14 μm wavelength range, we adopted a Fourier infrared camera to observe the infrared radiant area. Its corresponding temperature values were positively correlated with infrared intensity. It can be seen from Figs. 4(a) and 4(c) that the infrared emitting area was uniformly distributed on the surface of PZT/graphene heterostructure, and a linear increase was produced with the increase of external bias voltages in Figs. 4(b) and 4(d). Benefiting from its surface potential of PZT ferroelectric film substrate, higher carrier concentrations and mobility can be acquired when the Fermi level of graphene is tuned by a polarized substrate. Larger current and stronger electron–phonon interaction will lead to more obvious infrared emitting phenomenon in the graphene/PZT heterostructure. As a result of that, the graphene on mica substrate and PZT substrate has presented uniform and stable maximum temperatures of 42.9°C and 180.3°C, respectively. More pronounced infrared images also can be presented at the graphene/PZT heterostructure under the same bias voltage. A better linear temperature–voltage curve means more reliable control ability for applications [Fig. 4(d)]. For comparison, we also provide graphene infrared testing on the ${\mathrm{SiO}}_2/\mathrm{Si}$ substrate, which just exhibits 25.6°C under the 18.6°C room temperature condition at 11 V bias voltage. The graphene/PDMS structure presented maximum temperature 28.8°C under the 24.8°C room temperature condition at 11 V bias voltage. The results further verify that the ferroelectric substrate has huge potential for enhancing the infrared emission efficiency of graphene.

Response time is another important factor for the infrared emitting source. Just as described above, the electron–phonon coupling interaction caused by external voltage realizes the infrared signal emission. Current values reflected the ability of carrier mobility. By tuning the response time of the impulse current, the temperature of the graphene/PZT heterostructure can be synchronously regulated (Visualization 1). Figure 5(a) exhibits 40 ms rise time and 30 ms fall time when subjected to pulsed current excitation. Figure 5(b) shows the corresponding temperature impulse signals for the same sample excited by external bias voltage. Its temperature was varied from 26°C to 172°C within $\sim 0.96\mathrm{s}$. And the fall time from 172°C to 26°C was $\sim 0.98\mathrm{s}$. If the half of maximum value is set as the endpoint, then rise and fall times of graphene/PZT heterostructure will be $\sim 250$ and $\sim 330\mathrm{ms}$, respectively. We also provided a step test of external excited voltage and temperature values [Fig. 5(c)] for directly observing the following ability. Although some time delays were produced because of the generation and escape of heat, the heterostructure still reflected good followability and consistency in thermal radiation. Based on Wien’s displacement law, ${\lambda }_{m}T=a$, in which ${\lambda }_m$ is the peak wavelength of blackbody spectral emissivity, $T$ is the absolute temperature of the black body, and $a$ is 2897.8 μm·K. Then its temperature can reflect the corresponding thermal infrared emission wavelength and intensity. With the help of a Fourier infrared camera and external control circuit, a stable temperature value of $\sim 1041\mathrm{K}$ ($\sim 768°\mathrm{C}$) and a maximum temperature value of 1173 K ($\sim 900°\mathrm{C}$) were recorded. The Umklapp phonon–phonon scattering effect at high temperatures results in a significant reduction in the thermal conductivity of graphene, which suppresses lateral heat dissipation. And the vertical thermal conductivity of the graphene integrated on the PZT substrate is also suppressed because of poor heat transfer efficiency of PZT film and graphene crystal. Then produced heat cannot be effectively conducted out, but is localized in the center of the heterostructure, resulting in the localization of a large numbers of high-energy electrons. The bright white light was therefore greatly emitted based on the high-energy electrons falling back from high-energy state to low-energy state and electron–phonon coupling enhancement. More important is that very bright white light was observed by the naked eye. Its switch between indoor temperature and $\sim 900°\mathrm{C}$ will be finished within $\sim 1.2\mathrm{s}$. Its excellent thermal infrared emission properties and reliable fabrication methods exhibit huge potential in light engineering. Considering its application reliability, more cycles were tested for durability application verification. Here, 2000 cycles were carried out to check the reliability of infrared emitter at 11 V excitation voltage. During all the tests, the output current values were almost the same without attenuation, which verified a reliable application condition. We also characterized infrared radiation properties of graphene integrated on ${\mathrm{SiO}}_2/\mathrm{Si}$ wafer, mica slice, and flexible PDMS substrate film. The PZT/graphene heterostructure is far beyond the other structures mentioned above, which resulted from enhanced interface interactions of graphene on polarized ferroelectric PZT substrate, which leads to efficient phonon transport and electron–phonon coupling mechanisms.

Morse code is an on–off signal code that expresses different letters, numbers, and punctuation symbols through different orders of arrangement. Infrared communication has significant advantages such as anti-electromagnetic interference and strong concealment. The important information could be sent reliably based on the Morse mode method in the infrared frequency band. The traditional infrared LED source has a short transmission distance less than 7 m, which limits its further applications in optical communications. It is an important research topic to enhance the infrared signal intensity and transmission distance. Here, we fabricated a square graphene/PZT emitting unit with $3\mathrm{mm}\times 3\mathrm{mm}$ area. Brighter mid-infrared light could be observed easily by a Fourier infrared camera. Figure 6(a) shows the optical image of the camera and infrared source with a transmission distance of 20 m. Figures 6(b) and 6(c) show output current signals and temperature signals according to Morse code arrangement. The transmitting and receiving mode of infrared optical information mainly depends on visibility of the infrared light source. Figures 6(d)–6(g) display the images of the infrared source at 1 m, 5 m, 10 m, and 20 m, respectively. The transmission distance is better than that of the current common infrared wireless communication devices.

Uniform and highlighted multipixel display is another important research content. Five infrared units could be controlled simultaneously to produce obvious radiation images. With the increase of bias voltage, all infrared units tend to be brighter emission signals. Five infrared emission sources were encapsulated with ceramic package and glass window [Fig. 7(a)]. Its control circuit can be realized in series or a parallel way through the bottom breadboard. More infrared emission units can be introduced to further enrich its image composition and information transfer efficiency. Figures 7(b)–7(d) show the infrared display array, and its temperature values were directly extracted from Fourier infrared image processing software. The average temperatures of Figs. 7(b)–7(d) were 116.64°C, 140.5°C, and 160.38°C, respectively at 7 V, 9 V, and 11 V. The maximum difference of temperature of Figs. 7(a)–7(d) was 34.2°C, 61.9°C, 72.6°C, and 72.6°C limited by graphene uniformity and manufacturing accuracy in the laboratory. For evaluating sample-to-sample variability, we have fabricated 10 infrared emitters for testing its infrared signals and temperature values at three bias voltages. The maximum temperatures of 10 samples at 4 V, 8 V, and 10 V bias voltages were collected and compared (data not shown). The average temperatures of three temperature stages are 53.83°C, 91.64°C, and 155.38°C. Thestandard deviation of the three temperature stage is equal to 6.6°C, 14.1°C, and 10.6°C. Limited by errors introduced by the laboratory device fabrication process, the devices have different resistance values and carrier transfer efficiencies. With the increase of voltage, the difference of electric power of different devices will become larger under the same voltage. In the experiments, resistance compensation modules could be used to tune the infrared emitting intensity or power for stable and bright display.

Despite the temperature difference, the graphene/PZT emitting source still presented obvious infrared optical images. Different from impulse optical signals for information transmission in Fig. 6, the introduction of spatial images could speed up the efficiency of information transmission. Just as shown in Fig. 7(e), points and lines could be switched by an external tunable circuit in milliseconds. Three letters “N, U, C” could be transmitted within a shorter time, which greatly improves the efficiency of information transmission relying on the infrared frequency band.

Graphene has unique energy band structure and excellent dynamic tunable characteristics. By systematically studying the electron–phonon interaction process in graphene crystal film, PZT/graphene heterostructure was selected to construct a high-performance emission unit. Ultra-wide near–mid–far infrared spectra were excited by external bias voltage. Inter-band transition and phonon vibration are essential reasons for wide spectrum infrared signals. Higher carrier mobility [$\mathrm{11,361.55}{\mathrm{cm}}^2/(\mathrm{V}\cdot \mathrm{s})$] and phonon transport efficiency of PZT/graphene heterostructure promote maximum working temperature $\sim 1041\mathrm{K}$ ($\sim 768°\mathrm{C}$) and limiting temperature 1173 K ($\sim 900°\mathrm{C}$) in the air environment. The heterostructure also exhibits high reliability (2000 cycles) and switching time ($\sim 299$ to 445 K within $\sim 0.96\mathrm{s}$ rise time and $\sim 0.98\mathrm{s}$ fall time). By consulting relevant literature, the infrared emitting structure was first proposed and systematically tested. A reliable fabrication process and theoretical research is helpful for its practical applications (Visualization 1). Then a $3\mathrm{mm}\times 3\mathrm{mm}$ infrared unit was used for “N, U, C” letters transmission at 20 m distance. Combining with its spatial image display properties, its information efficiency will be further promoted. Compared with the laser communication collimation problem and low emission intensity of the traditional LED device, the PZT/graphene heterostructure may provide a new solution method in theory and engineering application.