Preparation of ZnGa₂O₄ nanoflowers and their full-color luminescence properties

Abstract

Gallate material, a luminescent matrix with excellent performance is normally prepared by vapor deposition or solid phase sintering method at high temperature. However, it has not been solved to prepare gallate-based fluorescent materials with full-color luminescent properties at low temperature. In this paper, ZnGa₂O₄ undoped or doped with Cr or Mn nanoflowers composed of nanosheet-level structure were prepared by hydrothermal method at low temperature. Under ultraviolet light irradiation, ZnGa₂O₄, ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄:Cr³⁺ display three primary colors of blue, green and red luminescence through self-excitation, Mn²⁺ and Cr³⁺ excitation respectively. The solid fluorescence yields of blue, green, and red colors are 32.3, 36.5, and 40.7%, respectively. It is highly expected to be applied to color display, biological imaging, white light devices.

Introduction

In recent years, inorganic luminescent materials have attracted people's attention because of their wide applications in fluorescence imaging, color display, white Light Emitting Diodes (LEDs) and so on^1–3. Therefore, constructing and designing efficient inorganic luminescent materials has become a hot topic for material scientists. Zinc gallate (ZnGa₂O₄), a ternary spinel material with a band gap of 4.4–4.7 eV, has exhibited excellent potential in future display system due to its prominent blue emission, high chemical and thermal stability, and good cathodoluminescence characteristics at low-voltage^4,5. Compared with other luminescent materials, zinc gallate can be self-excited by Ga-O group, and has blue light emission^6,7. ZnGa₂O₄ can also be used as the matrix of fluorescent materials, which has high luminous efficiency and narrow spectral band. The luminescent color can be changed by adjusting the surface properties^4,8 and composition of fluorescent materials^9,10, or by doping the dopant activators^11,12. Most fluorescent materials use rare earth metals as activators, such as Eu³⁺, Tb³⁺, Y³⁺, etc.^13–15, but rare earth metals are expensive and lack of resources. Previous studies have shown that transition metal ions Mn²⁺ and Cr³⁺ can be used as activators of fluorescent materials, such as ZnGa₂O₄:Mn²⁺ emitting green fluorescence and ZnGa₂O₄:Cr³⁺ emitting red fluorescence^11,16,17. Various synthetic methods have been adopted to synthesize these fluorescent materials, such as thermal evaporation¹⁸, solid-state reaction method¹⁹, Chemical Vapor Deposition (CVD), Atomic Layer Deposition (ALD) and so on²⁰. These synthetic methods usually require high reaction temperature, which is over 900 °C, so the energy consumption is high, which brings hidden dangers to environmental pollution control. Therefore, it is an urgent problem to find a low-temperature synthesis method for energy saving and emission reduction in the field of synthesis of full-color luminescent materials.

In this paper, undoped (ZnGa₂O₄), Mn²⁺-doped (ZnGa₂O₄:Mn²⁺) and Cr³⁺-doped (ZnGa₂O₄:Cr³⁺) nano-luminescent materials have been synthesized at low temperature by one step hydrothermal method under the template action of ethylenediamine. These luminescent materials are composed of 5 μm-sized nano-flowers, each of which is composed of 6–10 nm nanoflake hierarchical structure. Under ultraviolet irradiation, ZnGa₂O₄, ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄:Cr³⁺ display three primary colors of blue, green and red through self-excitation, Mn²⁺ excitation and Cr³⁺ ion excitation, respectively.

Methods

Raw materials and reagents

Gallium nitrate hydrate (Ga(NO₃)₃·xH₂O), Zinc acetate dihydrate (Zn(CH₃COO)₂·2H₂O), Manganese acetate tetrahydrate (Mn(CH₃COO)₂·4H₂O), Chromium nitrate nonahydrate (Cr(NO₃)₃·9H₂O), and Anhydrous ethylenediamine (NH₂(CH₂)₂NH₂) are analytically pure and boughten from Sigma-Aldrich Shanghai trading Co., Ltd.. Anhydrous ethanol (CH₃CH₂OH), ≥ 99.9% are boughten from Shanghai Sinopharm Chemical Co., Ltd. All reagents were not further treated before use. Water used in the experiment is Milli-Q ultrapure water.

Sample preparation

Synthesis of ZnGa₂O₄

Ga(NO₃)₃·xH₂O 0.512 g (2 mmol) and Zn(CH₃COO)₂·2H₂O 0.220 g (1 mmol) are added into 20 mL deionized water, magnetically stirred for 20 min at room temperature. And then 10 mL anhydrous ethylenediamine is added into the above solution, with continue stirring for 20 min. The mixed solution is transferred to a 50 mL reaction kettle and placed into an oven, and stirred at 220 °C for 12 h. The white precipitate was obtained by washed with water and absolute ethanol several times, and dried at 60 °C for 12 h.

Synthesis of ZnGa₂O₄:Mn²⁺

Ga(NO₃)₃·xH₂O 0.512 g (2 mmol) and Zn(CH₃COO)₂·2H₂O 0.220 g (1 mmol) are added into 17.5 mL deionized water, magnetically stirred for 20 min at room temperature. And then 2.5 mL Mn(CH₃COO)₂ solution with a concentration of 4 mmol L⁻¹ is added to above solution so that the concentration of Mn²⁺ is 1% of that of Zn²⁺, and magnetically stirred at room temperature for 20 min. Next, 10 mL anhydrous ethylenediamine is added into the above solution, with continue stirring for 20 min. The mixed solution is transferred to a 50 mL reaction kettle and placed into an oven, and stirred at 220 °C for 12 h. The white precipitate was obtained by washed with water and absolute ethanol several times, and dried at 60 °C for 12 h.

Synthesis of ZnGa₂O₄:Cr³⁺

The method is as same as the preparation of ZnGa₂O₄:Mn²⁺, and finally the concentration of Cr³⁺ is 0.5% of that of Zn²⁺.

Sample characterization

The phase structure of the sample was determined at room temperature by X-ray powder diffraction analyzer (Rigaku D/Max 2200PC, graphite monochromator filter, Cu Kα radiation, λ = 0.1542 nm) with the condition of tube voltage 40 kV, the tube current 20 mA, the scanning range 10°–80° (2θ) and the scanning speed 10 min⁻¹. The morphology and microstructure of the product were characterized by transmission electron microscope (JEM-100CXII, accelerating voltage 80 kV), high resolution transmission electron microscope (Philips Tecnai 20U-TWIN, accelerating voltage 200 kV) and scanning electron microscope (FE-SEM, S-4800, Hitachi, accelerating voltage 5 kV). X-ray photoelectron spectrometer (PHI-5300 ESCA spectrometer, Perkin Elmer, Al Kα as excitation light source) was used to analyze the surface properties of the samples. Before the spectrogram analysis, the electron binding energies of all elements were corrected with the C_1s peak at 284.6 eV as reference. Photoluminescence (PL) and fluorescence lifetime of samples were measured by Agilent Cary Eclipse Fluorescence Spectrometer. The UV–Vis absorption spectrum of the sample at room temperature was tested by Agilent Cary Series UV-VIS spectrometer, and BaSO₄ was used as baseline correction before the test. The infrared spectrum of the sample was tested by NICOLET FT-IR spectrometer, and the KBr was used as the background.

Results and discussion

Phase structure and morphology characteristics

ZnGa₂O₄ is a bimetallic oxide composed of ZnO and Ga₂O₃, with Fd-3m space group symmetry, a = b = c = 8.335, and spinel structure with chemical formula AB₂O₄, in which Zn²⁺ occupying tetrahedral center, Ga³⁺ occupying octahedral center²¹, as shown in Fig. 1a. Usually, the charge imbalance caused by the introduction of impurity ions is unfavorable to the luminous intensity of luminophores, so higher energy is needed to eliminate the charge imbalance, such as calcination at high temperature for a long time²². The effective compensation factor φ when ions are substituted was calculated according to the formula φ = Z/r, in which Z is the charge number of ions and r is the effective radius of ions²³. The greater the difference of φ, the more difficult it is to substitute ions. As shown in Table S1, for hexa-coordinate substitution of Mn²⁺, the effective compensation factor φ is 2.41, which is much lower than that of Ga³⁺ 4.83, so it is difficult for Mn²⁺ to replace Ga³⁺, while easy to replace Zn²⁺ due to the small difference of effective compensation factor^11,17. Furthermore, in the substitution reaction of ZnGa₂O₄, ions with similar effective radii are easy to be substituted with each other, that is, Mn²⁺ replaces Zn²⁺ to produce four coordinate substitutions, and Cr³⁺ replaces Ga³⁺ to produce six coordinate substitution^17,24.

Figure 1.

(a) Cubic spinel structure of ZnGa₂O₄, SEM images of (b-c) ZnGa₂O₄, (d–e) ZnGa₂O₄:Mn²⁺ and (f–g) ZnGa₂O₄:Cr³⁺, TEM images of (h) ZnGa₂O₄, (i) ZnGa₂O₄:Mn²⁺, (j) ZnGa₂O₄:Cr³⁺ (k) HRTEM image of ZnGa₂O₄, with the inset showing the corresponding SAED patterns.

The SEM photos of the three nanomaterials (ZnGa₂O₄, ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄:Cr³⁺) with different magnification is shown in Fig. 1b–g. They all present a flower-like nanostructure of about 5 μm, which is composed of multiple nanosheet-level substructures with a thickness of 6–10 nm interspersed together. The difference between the three samples is that the nanosheets composed of ZnGa₂O₄ are thicker and the degree of curling of the nanosheets is smaller, while the nanosheets doped with Mn²⁺ and Cr³⁺ are thinner, and the nanosheets are freely curled to form spherical nanoflowers. As shown in Fig. S1. Zn, Ga, O and the corresponding doped elements Mn and Cr are uniformly distributed in the flower-like nanostructures confirmed by the element distribution surface scans. The flower-like structure of ZnGa₂O₄, ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄:Cr³⁺ can also be seen from the TEM photos in Fig. 1h–j. Each flower is composed of the sub-structure of nano-flakes, and the size of nano-flowers is about 5 μm. From the contrast of the electron microscope photos, it can be clearly seen that the nano-flakes constituting the flower-like structure become thinner in turn, which is similar to that of Scanning electron microscope (SEM). The phenomenon may be due to the impurity ions adsorbed on the initial grain surface during hydrothermal process, which inhibiting the crystallization of the material to some extent, preventing the grain growth in some directions, and resulting in the formation of thinner nanosheets. High-resolution photos and corresponding selective electron diffraction photos of ZnGa₂O₄ are shown in Fig. 1k. The lattice spacing 0.44 nm is corresponding to the (200) crystal plane of ZnGa₂O₄, and the selective electron diffraction photo clearly shows single crystal structure of a ZnGa₂O₄ nanoflake. In the single crystal structure of the sheet, the diffraction points correspond to (200) and (111) crystal plane. The direction of the crystal zone axis is confirmed to [011] by calculating, therefore the exposed surface of the nanoplate is (110) plane.

As shown in Fig. 2a the diffraction peaks of ZnGa₂O₄, ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄:Cr³⁺ all correspond to the diffraction peaks of standard card JCPDS38-1240 ZnGa₂O₄, which are cubic spinel structure. After doping Mn²⁺ and Cr³⁺, the intensity of the diffraction peak decreases, and the corresponding FWHM (full width at half maximum) increases in sequence. The results of X-ray diffractometer (XRD) analysis also indicate that the secondary structure nanosheets that make up the nanoflowers become thinner in turn after doping Mn²⁺ and Cr³⁺, which consistent precisely with the observation results of SEM and transmission electron microscopy (TEM). As shown in Fig. 2b–e the electron binding energies of 2p_1/2 orbitals and 2p_3/2 orbitals of Ga are located at 1143.6 eV and 1116.8 eV, respectively. And the electron binding energies of 2p_1/2 orbitals and 2p_3/2 orbitals of Zn are located at 1043.8 eV and 1021.1 eV, respectively. The characteristic peaks of electron binding energies located at 654.4 eV and 645.5 eV belong to 2p_1/2 orbitals and 2p_3/2 orbitals of Mn, respectively and manganese ions show +2 valences. The characteristic peaks of electron binding energy at 586.5 eV and 576.5 eV respectively belong to 2p_1/2 orbitals and 2p_3/2 orbitals of Cr and chromium ions show +3 valences. The intensity of these characteristic peaks is small due to the low contents of Mn and Cr.

Figure 2.

(a) XRD patterns of ZnGa₂O₄, ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄:Cr³⁺. The XPS spectra of ZnGa₂O₄, ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄: Cr³⁺: (b) Zn 2p, (c) Ga 2p, (d) Mn 2p in ZnGa₂O₄:Mn²⁺ and (e) Cr 2p in ZnGa₂O₄:Cr³⁺.

Infrared and ultraviolet spectral characteristics

In order to understand the chemical composition of the sample, the Fourier transform infrared spectrum is conducted. The Fourier Transform infrared spectroscopy (FT-IR) of ZnGa₂O₄, ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄:Cr³⁺ in Fig. S2 also indicate the samples were binary metal oxides consisting of Zn-O and Ga-O groups. As showed in Fig. S2, the broad absorption peak at the 3445 cm⁻¹ wavelength belongs to the stretching vibration of O-H and N-H. The stretching vibration of N-H may come from the residual ethylenediamine in the sample, but there is no obvious stretching vibration peak of it near 1190 cm⁻¹. Therefore, the residual ethylenediamine may be very small and can be ignored after repeated cleaning of water and anhydrous ethanol. In the fingerprint region at low wavelength, the larger peaks of 585 cm⁻¹ and 425 cm⁻¹ are attributed to the vibration absorption of Zn-O and Ga-O, respectively. Through the infrared spectrum analysis, no other vibration peaks are observed except Zn-O and Ga-O in the sample, so it is determined that the sample is a binary metal oxide composed of Zn-O group and Ga-O group. The UV-vis absorption spectra of ZnGa₂O₄, ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄:Cr³⁺ samples are shown in Fig. S3. It can be seen from the figure that the absorption regions of the three samples are basically the same, and there is only absorption in the region smaller than 350 nm. It is also confirmed that ZnGa₂O₄ can only be excited at wavelengths less than 350 nm. However, in the 300–350 nm wavelength region, compared with the absorption peak of ZnGa₂O₄, the absorption of ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄:Cr³⁺ increases slightly, which may be due to the absorption of a small amount of Mn and Cr itself, because the amount of Mn²⁺ and Cr³⁺ is very small, only 0.4% and 1%, so the absorption of these two elements is also very weak.

Luminescent properties

The excitation and emission spectra of ZnGa₂O₄, ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄:Cr³⁺ are shown in Fig. 3a–c. For undoped ZnGa₂O₄, three peaks can be seen in the excitation spectrum, which are located at 226 nm 239 nm and 257 nm, respectively. These excitation peaks are caused by the charge transfer from O²⁻ to octahedral center Ga³⁺ and the ultraviolet absorption of ZnGa₂O₄ itself²⁵. The emission spectrum obtained using 226 nm as the excitation wavelength is a broad peak with the highest peak of 456 nm in the range of 340–750 nm. This broad emission peak is in all probability caused by the self-excitation of Ga-O hexahedron in the spinel structure. The luminescent properties of fluorescent host materials are usually changed by introducing impurity ions²⁶, that is also applicable to ZnGa₂O₄ host materials. Mn²⁺-doped ZnGa₂O₄ has green fluorescence emission, as shown in Fig. 3b. Except for the charge transfer from O^2- to Ga³⁺ in the octahedral center and the ultraviolet absorption of ZnGa₂O₄ itself, the absorption of Mn²⁺ excites a red shift of 32 near 300 nm, which is consistent with the analysis of ultraviolet-visible absorption spectrum in Fig. S3. Due to the activation of Mn²⁺, the emission spectrum with the highest emission peak of 505 nm is located in the range of 470–600 nm with the excitation wavelength of 226 nm.

Figure 3.

Excitation and emission spectra of (a) ZnGa₂O₄, (b) ZnGa₂O₄:Mn²⁺, (c) ZnGa₂O₄:Cr³⁺ and (d) photoluminescence decay curves and bi-exponential fittings for the ZnGa₂O₄, ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄: Cr³⁺.

After enlarged locally as shown in Fig. S4, the five smaller excitation peaks located between 351–443 nm and centered at 351 nm, 379 nm, 410 nm, 422 nm and 443 nm respectively correspond to ⁵A₁–⁴E, ⁶A₁–⁴T₂, ⁶A₁–⁴A₁, ⁴E₁ and ⁶A₁–₄T of Mn²⁺.²⁷ When excited at 226 nm, ZnGa₂O₄:Mn²⁺ has green emission at 505 nm, which belongs to the ⁴T₁–⁶A₁ d orbital electron forbidden transition of Mn^2+11,17. This is the process of energy transfer from ZnGa₂O₄ matrix to Mn²⁺²⁷. The transition process of ⁴T₁–⁶A₁ of Mn²⁺ is accompanied by strong 3d shell lattice vibration coupling, and is affected by crystal field and symmetric sites. If Mn²⁺ is in a weak crystal field, i.e. tetrahedron, the splitting of excitation energy will be weak, which will be accompanied by high energy emission, that is, green light and if Mn²⁺ is in a strong crystal field, i.e., octahedron, it will emit yellow or red light^17,27, which is consistent with our previous analysis of crystal structure. In our investigation, Mn²⁺ replaces Zn²⁺ with similar ionic radius in cubic ZnGa₂O₄ matrix to generate tetrahedral coordination and emit green light, which is completely consistent with the test results of fluorescence spectrum.

The excitation and emission spectra of ZnGa₂O₄:Cr³⁺ are shown in Fig. 3c. There is a wide excitation peak between 200–350 nm, including four intensity excitation peaks (226 nm, 240 nm, 257 nm, 266 nm), which related to the charge transfer transition of O²⁻ to the octahedral center Ga³⁺ and the absorption transition with the belt, and the excitation spectrum of 300–350 nm is caused by the absorption of Cr³⁺. A red emission peak at 696 nm was obtained by excitation at 226 nm, which was attributed to the ²E–⁴A₂ characteristic transformation of Cr³⁺²⁸. Meanwhile, a similar red emission peak at 696 nm was obtained by excitation at 416 nm and 572 nm. These two excitation peaks at 416 nm and 572 nm are caused by d–d electron-electron transitions of Cr^3+24,29, corresponding to the ⁴A₂–⁴T₁ and ⁴A₂–⁴T₂ characteristic transitions of Cr³⁺, respectively³⁰.

Undoped, Mn²⁺ doped and Cr³⁺ doped ZnGa₂O₄ have blue, green and red emission properties under ultraviolet (UV) excitation, respectively. The excitation wavelengths used in the emission spectra of ZnGa₂O₄, ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄:Cr³⁺ are all 226 nm, indicating that the hetero ions in ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄:Cr³⁺ can effectively enter the lattice of ZnGa₂O₄ under hydrothermal conditions to replace Zn²⁺ and Ga³⁺ to form tetrahedral and octahedral coordination, respectively. This is related to the addition of an appropriate amount of ethylenediamine during hydrothermal. Ethylenediamine aqueous solution is a strongly alkaline solution, which plays an effective role in promoting the crystallization of materials and the entry of hetero ions into the crystal lattice of the matrix under the condition of hydrothermal high temperature and high pressure. We also conduct experiment keeping other conditions remaining the same without ethylenediamine in the synthesis. The obtained ZnGa₂O₄ doped with Mn²⁺ and Cr³⁺ does not show green and red emission properties after UV excitation, indicating that it is difficult for hydrothermal hetero ions to enter into the lattice of ZnGa₂O₄ matrix under the condition of non-strong alkaline solvent.

The fluorescence attenuation curves of ZnGa₂O₄, ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄:Cr³⁺ are fitted exponentially as shown in Fig. 3d. The attenuation curves of the three samples are all fitted by double exponents, which are in accordance with the formula.

$$I=I_1\text{exp}\left(-t/{\tau }_1\right)+I_2\text{exp}\left(-t/{\tau }_2\right)$$ 1

where I is the fluorescence intensity when the time is t, I₁ and I₂ are fitting constants, and τ₁ and τ₂ are fluorescence lifetime. After fitting, each sample corresponds to two millisecond lifetimes, a shorter lifetime τ₁ and a relatively longer life τ₂. The specific fitting parameters are shown in Table S2. The longer lifetimes of each sample of ZnGa₂O₄, ZnGa₂O₄:Mn₂₊ and ZnGa₂O₄:Cr³⁺ correspond to the self-excitation of Ga-O in the bulk phase of luminescent materials, the ⁴T₁-⁶A₁ transition of Mn²⁺ and the ²E–⁴A₂ transition of Cr³⁺, respectively. The short lifetime of the three samples is due to the fact that the surface effect of the materials has a great influence on the luminescence lifetime. These materials are all composed of ultra-thin 6–10 nm nanosheets with large surface area, and the increase of surface atoms leads to the appearance of more activated ions on the surface of the nanosheets. However, the impurities, unsaturated bonds, vacancies and other surface defects on the surface of the nanoparticles will quenched the activated ions and lead to radiation-free transition, thus shortening the life of the activated ions.⁸

Excited by 254 nm's handheld UV lamp, ZnGa₂O₄, ZnGa₂O₄:Mn²⁺ and ZnGa₂O₄:Cr³⁺ appear bright blue, green and red, respectively. Their optical photos are shown in Fig. 4a. The solid fluorescence yields of blue, green, and red colors are 32.3, 36.5, and 40.7%, respectively. Under the light excitation of 226 nm wavelength, the Normalized fluorescence emission spectra of the three materials are shown in Fig. 4b. The maximum fluorescence emission spectra of the three materials are located in 456 nm, 505 nm and 696 nm, respectively, which basically correspond to the central regions of blue, green and red. Their emission spectra are imported into the CIE color coordinate software, respectively, and the color coordinate diagram shown in Fig. 4c is obtained. The color coordinates are located at (0.19, 0.23), (0.10, 0.65) and (0.66, 0.34), respectively, which indicates that any color including white in the triangular area connected by the three points can be obtained by changing the ratio of the three luminescent materials.

Figure 4.

(a) Digital images of ZnGa₂O₄, ZnGa₂O₄:Mn²⁺, and ZnGa₂O₄:Cr³⁺ on glass substrates under UV light excitation. (b) Normalized PL emission spectra of ZnGa₂O₄, ZnGa₂O₄:Mn²⁺, and ZnGa₂O₄:Cr³⁺ samples. (c) The for ZnGa₂O₄ (0.19, 0.23), ZnGa₂O₄:Mn²⁺ (0.10, 0.65), and ZnGa₂O₄:Cr³⁺ (0.66, 0.34) samples.

In order to demonstrate whether there is white luminescence phenomenon when mixing the three samples, we conducted packaged white LED luminescence testing on their mixture. As shown in Fig. 5a, the encapsulated white LED device and the emitting color are shown. The encapsulated white LED prepared has a correlated colour temperature (CCT) of 26702K and a color rendering index (CRI) of 55.1. Within the constant voltage range of 20 mA to 120 mA and 3 V, the relationship between the luminous intensity of the encapsulated white LED and the input forward current is shown in Fig. 5b. From the color of the encapsulated white LED device and the CIE chromaticity diagram, we can see that the light emitted by this mixture is not pure white light, but a cyanish white-like light. According to the emission spectrum of the mixture, we speculate that the reason is that the emission wavelength of red light is mostly in the invisible near-infrared region after 650 nm, and there is an empty window in the wavelength range of 600–650 nm, resulting in the emission color of encapsulated white LED being a cyan white light, rather than a pure white light like the results made by other phosphors^31,32.

Figure 5.

(a) Encapsulated white LED devices and emitting colors. (b) The relationship between the luminous intensity of packaged white LED and the input forward current.

Conclusions

ZnGa₂O₄ nanoflowers with single size composed of ZnGa₂O₄ flake substructures with a thickness of 6-10 nm were synthesized by a simple hydrothermal method under the action of ethylenediamine template. The luminescence color of ZnGa₂O₄ is controlled by doping Mn²⁺ and Cr³⁺. Under UV excitation, undoped ZnGa₂O₄, ZnGa₂O₄ doped with Mn²⁺ and Cr³⁺ have blue, green and red emission properties, respectively. The luminescence properties of the same matrix material with three primary colors are obtained. The blue, green and red fluorescence comes from the self-excited electron transfer of Ga-O itself and the 3d electron energy transfer of Mn²⁺ and Cr³⁺. The three samples are mixed to do the encapsulated white LED luminescence test, which has the phenomenon of cyan white luminescence. These ZnGa₂O₄-based fluorescent nanomaterials are expected to be used in color display, biological imaging and white light devices.

Author contributions

Y.L.: Conceptualization, methodology, formal analysis, investigation, writing—original draft, writing—review and editing, T.Z.: conceptualization, data curation, formal analysis, funding acquisition, methodology, supervision, writing-original draft, writing-review & editing. X.Z.: supervision, conceptualization, methodology, invisualization, writing-review & editing. C.C.: supervision, conceptualization, methodology, invisualization, writing-review & editing.

Data availability

All data generated or analyzed during this study are included in this published article (and its Supplementary Information files).

Competing interests

The authors declare no competing interests.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-023-41658-5.