The authors thank the funding of the National Natural Science Foundation of China (82001945), the Shanghai Pujiang Program (20PJ1410700), and the starting grant of ShanghaiTech University. The authors thank the Centre for High-resolution Electron Microscopy (ChEM), School of Physical Science and Technology, ShanghaiTech University (No. EM02161943) for the material characterization support. The authors thank the Analytical Instrumentation Center (#SPST-AIC10112914), School of Physical Science and Technology, ShanghaiTech University for the spectral test support and XRD test support. The authors also thank Prof. Jianfeng Li for the help with the material characterizations.

1. Synthesis of Zn2GeO4: Mn PLNPs
<ol>
	<li>Prepare 2 M/L sodium hydroxide solution by dissolving 10 mM sodium hydroxide in 5 mL of deionized water.</li>
	<li>Prepare 0.4 M/L sodium germanate solution by adding 2 mM of germanium oxide into 5 mL of sodium hydroxide solution, and then stir at room temperature for about 30 min.</li>
	<li>Add 4 mM of zinc chloride, 0.01 mM of manganese nitrate and 600 &#181;L of nitric acid (65%-68%, wt) to a 100 mL small beaker conta...

Hydrothermal Synthesis of Persistent Luminescent Nanoparticles

This article introduces a synthesis method for persistent luminescent nanomaterials and polymerization for color rendering applications. The materials showed extremely stable optical properties and a visible afterglow after ceasing excitation of ultraviolet light. A persistent luminescent nanomaterial (Zn2GeO4: Mn) was prepared using a hydrothermal method with different pH (Figure 1A). The TEM image showed that ZGO: Mn PLNPs whose pH is 9.4 were rod-shaped with an avera...

Persistent luminescence (PL) is a unique optical process that can store energy from ultraviolet light, visible light, X-rays, or other excitation sources and then release it in the form of photon emission for seconds, minutes, hours, or even for days1. The discovery of continuous luminous phenomenon originated from the Song dynasty in ancient China 1000 years ago when a painter accidentally discovered a painting that glowed in the dark. It was later found that some natural raw materials and minerals could absorb sunlight and then glow in the dark and can even be made into fascinating glowing pearls2. However, the first adequate record of persistent phosphors needed to be traced back to the discovery of PL emission from Bologna stone in the early 17th century, which gave off a yellow to orange afterglow in the dark1,2,3,4. Later, it was discovered that the natural impurities of Cu+ in BaS played an important role in this persistent luminescence phenomenon1,4. Until the mid-1990s, the production of persistent phosphors was largely limited to sulfides5. In 1996, Matsuzawa et al. reported a new metal oxide (SrAl2O4:Eu2+, Dy3+) phosphor showing extremely bright afterglow, which greatly stimulated the expansion of persistent luminescence research6.
The unique properties of persistent luminescent materials are mainly derived from two kinds of active centers: emission centers and trap centers1,7,8. Among them, the former determines the emission wavelength, while the sustained intensity and time are mainly determined by the trap centers. Therefore, the design of PL materials should take both aspects into consideration in order to achieve the desired emission wavelength and long-lasting luminescence9,10. The emission centers can be lanthanide ions with 5d to 4f or 4f to 4f transitions, transition metal ions with d to d transitions, or post-transition metal ions with p to s transitions1,11,12,13. On the other hand, trap centers are formed by lattice defects or various co-dopants14,15, which usually do not emit radiation but instead store the excitation energy for a while and then gradually release it to the emitting center through thermal or other physical activation16,17. Many phosphors with different hosts and dopant ions have been reported. So far, inorganic metal compounds18, metal-organic frameworks8, certain organic composites19, and polymers20 have been found to have PL properties. In recent years, deep trap persistent luminescent materials with controllable energy storage and photon release properties have shown great potential applications in information storage21, multi-layer anti-counterfeiting22, and advanced displays23.
Based on the above composition, PLNPs with various matrices have been successfully designed and synthesized, such as BaZrSi3O97, Y2O2S24, Ca14Mg2(SiO4)825, CaAl2O426, SrAl2O426,27 , and Sr2MgSi2O728 with multi-doped luminescent centers, in which the luminescence centers strongly depend on the crystal field effect of the host lattice, while the defects generated or improved by different doping serve as auxiliary centers to control the afterglow intensity and duration. In addition to co-doping, long-lasting emission can also be observed in the case of only one activator, such as heterogeneous PLNPs with the matrix of Y3Al2Ga3O1229, BaGa2O430, Ca2SnO431, CdSiO332 , and Zn3Ga2Ge2O1033. Germanate-based ternary oxides include Ca2Ge7O16, Zn2GeO4, BaGe4O9, etc., which are typical wide-bandgap semiconductor materials with tunable emission, reproducible and stable luminescence, high quantum yield, environmental friendliness and wide availability34,35,36. These advantages make it a good activator-type photoluminescent carrier. In the past few years, germanates with various microstructures35,37, have been prepared by conventional solid-state reactions or chemical solution methods, and these characteristics make Zn2GeO4 useful in sterilize38, anti-counterfeiting39, catalysis40, light diodes41 , biosensing42, battery anodes43, detectors44,45, etc.
In order to expand the application of PL materials, the controllable synthesis of uniform and persistent luminescent nanoparticles has been developed. A decade ago, persistent phosphors were synthesized by solid-state synthesis46. However, the long reaction time and high annealing temperature during the synthesis process resulted in large and irregular phosphors, which limited their application in other fields such as biomedicine. In 2007, Chermont et al. used sol-gel approach to synthesize nanoparticles for the first time and prepared Ca0.2Zn0.9Mg0.9Si2O6: Eu2+, Dy3+, Mn2+, which opened the era of PLNPs47. However, the top-down synthesis strategy is accompanied by problems such as uncontrollable size and morphology, so researchers have done a lot of work in the development of controllable bottom-up synthesis of PLNPs. Since 2015, various synthesis methods have emerged one after another, such as the template synthesis method, hydrothermal/solvent thermal method, sol-gel method and other wet chemical synthesis methods for the synthesis of uniform and controllable PLNPs47,48,49,50. Among them, hydrothermal synthesis is one of the most commonly used methods for preparing nanomaterials, which can provide an adjustable and mild synthetic method to prepare compounds or materials with special structures and properties51.
Here, we present a detailed experimental procedure for synthesizing Zn2GeO4: Mn PLNPs with 1D nanorods morphology via the hydrothermal method and providing them with a rigid environment for further illumination applications. It was found that the luminescence properties of PLNPs, including emission wavelength and afterglow decay curve, can be changed by adjusting the pH value of the precursor. On the other hand, to emphasize the versatility of this method, we also synthesize PLNPs with Cr as the luminescent center using ZnGa2O4 as the matrix (ZnGa2O4: Cr), which exhibits afterglow emission (697 nm) in the near-infrared region after being excited by ultraviolet light (365 nm). This article mainly focuses on Zn2GeO4: Mn whose pH value of precursor solution is 9.4 for two-dimensional and three-dimensional artworks production and visualization. Zn2GeO4: Mn is a type of nanomaterial with Mn ions as the luminescent center which obtains strong green light emission (~ 537 nm) under the excitation of 365 nm ultraviolet light. At the same time, the continuous green light can still be seen after stopping excitation. In order to promote the polymerization of PLNPs in methyl methacrylate, ligands (Poly-ethylene glycol) were added during the hydrothermal synthesis process, and then PLNPs were polymerized with methyl methacrylate (MMA) in a two-dimensional or three-dimensional mold so that it can form glowing artwork while smoothly demolding.
This protocol provides a feasible method for the hydrothermal synthesis, polymerization reactions, and luminescent applications of PLNPs in advanced color rendering. Any differences in pH, temperature, and chemical reagents during nanocrystal growth will affect the size and optical properties of PLNP nanostructures. This detailed protocol aims to help new researchers in the field to improve the reproducibility of PLNPs using a hydrothermal method for further wider applications.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>azobisisobutyronitrile (99%)</td>
			<td>Macklin</td>
			<td>A800354</td>
			<td>Further purification required</td>
		</tr>
		<tr>
			<td>methyl methacrylate(99%)</td>
			<td>Sigma-Aldrich</td>
			<td>M55909</td>
			<td>Further purification required</td>
		</tr>
		<tr>
			<td>deionized water</td>
			<td>Merck</td>
			<td>ZEQ7016T0C</td>
			<td>Milli-Q&#160;Direct Water Purification System</td>
		</tr>
		<tr>
			<td>alkaline aluminum oxide (100-200 mesh)</td>
			<td>Macklin</td>
			<td>A800033</td>
			<td></td>
		</tr>
		<tr>
			<td>&#160;ammonium hydroxide&#160; (25%-28%, wt)</td>
			<td>Macklin</td>
			<td>A801005</td>
			<td></td>
		</tr>
		<tr>
			<td>beaker&#160;</td>
			<td>Synthware</td>
			<td>B220100</td>
			<td></td>
		</tr>
		<tr>
			<td>chromium(III) nitrate nonahydrate (99.95%)</td>
			<td>Aladdin</td>
			<td>C116448</td>
			<td></td>
		</tr>
		<tr>
			<td>centrifuge</td>
			<td>ThermoFisher Scientific</td>
			<td>75004250</td>
			<td></td>
		</tr>
		<tr>
			<td>column</td>
			<td>Synthware</td>
			<td>C184464CR</td>
			<td></td>
		</tr>
		<tr>
			<td>digital camera</td>
			<td>&#160;Canon</td>
			<td>EOS M50 Mark II</td>
			<td></td>
		</tr>
		<tr>
			<td>electric thermostaticdrying oven</td>
			<td>Longyue</td>
			<td>LDO-9036A</td>
			<td></td>
		</tr>
		<tr>
			<td>ethanol (99.7%)</td>
			<td>Greagent</td>
			<td>1158566</td>
			<td></td>
		</tr>
		<tr>
			<td>gallium nitrate hydrate(99.9%)</td>
			<td>Aladdin</td>
			<td>G109501</td>
			<td></td>
		</tr>
		<tr>
			<td>germanium oxide (99.99%)</td>
			<td>Sinopharm Chemical ReagentCo., Ltd</td>
			<td>51009860</td>
			<td></td>
		</tr>
		<tr>
			<td>glass rod</td>
			<td>Sinopharm Chemical ReagentCo., Ltd</td>
			<td>91229401</td>
			<td></td>
		</tr>
		<tr>
			<td>powder X-Ray Diffractometer</td>
			<td>D2 PHASER DESKTOP XRD</td>
			<td>BRUKER</td>
			<td></td>
		</tr>
		<tr>
			<td>manganese nitrate (98%)</td>
			<td>Macklin</td>
			<td>M828399</td>
			<td></td>
		</tr>
		<tr>
			<td>methanol (99.5%)</td>
			<td>Greagent</td>
			<td>1226426</td>
			<td></td>
		</tr>
		<tr>
			<td>nitric acid (65.0-68.0%, wt)</td>
			<td>Sinopharm Chemical ReagentCo., Ltd</td>
			<td>10014508</td>
			<td></td>
		</tr>
		<tr>
			<td>pH meter</td>
			<td>Shanghai Leici Sensor Technology Co., Ltd</td>
			<td>PHS-3C</td>
			<td></td>
		</tr>
		<tr>
			<td>polyethylene glycol (300, Mw)</td>
			<td>Adamas</td>
			<td>01050882(41713A)</td>
			<td></td>
		</tr>
		<tr>
			<td>sealing film</td>
			<td>Parafilm</td>
			<td>2025722</td>
			<td></td>
		</tr>
		<tr>
			<td>sodium hydroxide (GR)</td>
			<td>Sinopharm Chemical ReagentCo., Ltd</td>
			<td>10019764</td>
			<td></td>
		</tr>
		<tr>
			<td>spectrometer</td>
			<td>Horiba</td>
			<td>Fluorolog-3&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>transmission electron microscope</td>
			<td>JEOL&#160;</td>
			<td>JEM-1400 Plus</td>
			<td></td>
		</tr>
		<tr>
			<td>transmission electron microscope</td>
			<td>JEOL</td>
			<td>2100 Plus&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>triangular funnel</td>
			<td>Synthware</td>
			<td>F181975</td>
			<td></td>
		</tr>
		<tr>
			<td>ultrasound machine</td>
			<td>centrifuge</td>
			<td>JP-040S</td>
			<td></td>
		</tr>
		<tr>
			<td>zinc chloride (98%)</td>
			<td>Greagent</td>
			<td>01113266/G81783A</td>
			<td></td>
		</tr>
	</tbody>
</table>

synthesis of persistent luminescent nanoparticles for rewritable displays and illumination applications

Persistent luminescent nanoparticles (PLNPs) possess the capabilities to maintain extended longevity and robust emission even after the excitation has ceased. PLNPs have been widely used across various domains, including information displays, data encryption, biological imaging, and artistic decoration with sustained and vivid luminosity, providing boundless possibilities for a variety of innovative technology and artistic projects. This protocol focuses on an experimental procedure for the hydrothermal synthesis of PLNPs. The successful synthesis of enduring luminescent nanomaterials with Mn2+ or Cr3+ serving as a luminescent center in Zn2GeO4: Mn (ZGO: Mn) or ZnGa2O4: Cr highlights the universality of this synthetic method. On the other hand, the optical properties of ZGO: Mn can be changed by adjusting the pH of precursor solutions, demonstrating the tunability of the protocol. When charged with ultraviolet (UV) at a wavelength of 365 nm for 3 min and then stopped, PLNPs exhibit the remarkable capacity to generate afterglow efficiently and consistently, which makes them ideal for making two-dimensional rewritable displays and three-dimensional transparent, luminous artworks. This protocol outlined in this paper provides a feasible method for the synthesis of persistent luminescent nanoparticles for further illumination and imaging applications, opening up novel prospects for the fields of science and art.

Author Spotlight: Advancing Bioimaging and Therapy with Functional Nanomaterials

Synthesis of Persistent Luminescent Nanoparticles for Rewritable Displays and Illumination Applications

Our research focuses on developing functional nanomaterials based on precise biotechnology. We aim to achieve bioimaging disease treatment, and physiological function regulation in a minimally invasive and highly selective fashion by using nano composites with luminescence, thermal magnetic, and acoustic properties. We have demonstrated that utilizing a rigid backbone chain polymer, polymethyl methacrylate as the matrix, purely polycyclic aromatic hydrocarbons can exhibit stable and exceptionally long phosphorescent lifetimes, showcasing purely organic room temperature phosphorescent properties.We expect that this protocol not only provide a detailed experimental procedure for the hydrothermal synthesis of long-lasting imaging nanomaterials, but also introduce the method for the copolymerization of persistent luminescent nanoparticles and MMA to further achieve ultraviolet mediated rewriteable and luminescent applications. The hydrothermal synthesis masses of persistent luminescent nanoparticles could restrict the application of certain temperature sensitive substance since they require relatively high reaction temperatures. Consequently, the selection of an appropriate synthesis method should be contingent on specific application and requirement.The main research directions in our laboratory include the development of temperature-sensitive luminescence nanoprobe for microscopic temperature monitoring, immune cells selective nanocomposite for immune imaging and therapy, and the establishment of new acoustic and magnetic responsive materials.

The synthesis diagram of Zn2GeO4: Mn (ZGO: Mn) PLNPs is shown in Figure 1. The amphiphilic polymer Poly-ethylene glycol (PEG) is added to modify the ligand-free Zn2GeO4: Mn (ZGO: Mn) nanorods to better dissolve in MMA medium. First, the transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) images of ZGO: Mn whose pH is 9.4 are collected (Figure 1), and then dynamic light scatt...

A protocol is presented for the synthesis of persistent luminescent nanomaterials (PLNPs) and their potential applications in rewritable displays and artistic processing utilizing the afterglow effect under ultraviolet light (365 nm) irradiation.

Persistent luminescent nanoparticles (PLNPs) possess the capabilities to maintain extended longevity and robust emission even after the excitation has ...