JAIST Repository
https://dspace.jaist.ac.jp/

Title

Photochromism and Long Persistent Luminescencein Pr^<3+>-Doped Garnet Transparent Ceramic via
Ultraviolet or Blue Light Up-conversion Charging

Author(s)Du, Qiping; Ueda, Jumpei; Zheng, Ruilin; Tanabe,
Setsuhisa

Citation

Advanced Optical Materials, 11(7): 2202612

Issue Date

2023-01-19

Type

Journal Article

Text version

author

URL

http://hdl.handle.net/10119/18800

RightsThis is the peer reviewed version of the following
article: Qiping Du, Jumpei Ueda, Ruilin Zheng, andSetsuhisa Tanabe, Advanced Optical Materials, 11,
7, 2202612 (2023), which has been published in
final form at
https://doi.org/10.1002/adom.202202612. This
article may be used for non-commercial purposes inaccordance with Wiley Terms and Conditions for
Use of Self-Archived Versions. This article may not
be enhanced, enriched or otherwise transformed
into a derivative work, without express permission
from Wiley or by statutory rights under applicablelegislation. Copyright notices must not be removed,
obscured or modified. The article must be linked to
Wiley’s version of record on Wiley Online Library
and any embedding, framing or otherwise making
available the article or pages thereof by third parties
from platforms, services and websites other thanWiley Online Library must be prohibited.

Description

Japan Advanced Institute of Science and Technology

Photochromism and Long Persistent Luminescence in Pr3+-Doped Garnet Transparent
Ceramic via Ultraviolet or Blue Light Up-conversion Charging
Qiping Du*, Jumpei Ueda*, Ruilin Zheng, and Setsuhisa Tanabe
Qiping Du, Jumpei Ueda, Ruiling Zheng, and Setsuhisa Tanabe
Graduated School of Human and Environmental Studies, Kyoto University, Kyoto, 6068301,
Japan
E-mail: du.qiping.18p@st.kyoto-u.ac.jp
Jumpei Ueda
Graduate School of Advanced Science and Technology, Japan Advanced Institute of Scienceand Technology, Ishikawa 923-1292, Japan
E-mail: ueda-j@jaist.ac.jp
Keywords: garnet transparent ceramic, photochromism, persistent luminescence, upconversion
Abstract: Multifunctional phosphors with photochromism and persistent luminescent (PersL)
properties have attracted increasing interest owing to the capability of absorbing the photon
energy and trapping the generated carriers via defects. However, the opacity of materials
compromises the enhancement of photochromism and PersL properties; besides, the need ofhigh energy excitation light source limits their applicability. To bridge these obstacles, wereport Pr3+-doped Y3Al2Ga3O12 transparent ceramic with in-line transmittance over 80% at
1800 nm, which exhibits strong red PersL after several minutes ultraviolet (UV) light or blue
light up-conversion charging. The luminance duration time can reach more than 7 h at 0.32 mcd/m2 threshold value after UV light charging. Interestingly, the phosphor also displays
photochromic properties with robust fatigue resistance, i.e., the color changes from light green
to red by UV/blue light illumination and is bleached at 300℃. The nature of trap centers,
trapping and detrapping processes are explored based on thermoluminescence and electron spinresonance. Finally, the mechanism of photochromism and PersL are discussed by using vacuum
referred binding energy diagram. This work opens new avenues for future research on
multifunctional materials and brings potential applications in optical information encryption
media and optical sensors.
11. Introduction
On the basis of an unprecedented explosion of the total mass amount of digital information data,
information storage has received increasing attention.[1] Growing endeavors have been made to
develop sustainable and versatile optical data storage and conversion materials due to theiradvantages, i.e., high storage density, long lifetime, easy portability, and exceptional
rewritability in recent years.[2] Photochromism is the phenomenon that the material changes its
color by the illumination of light.[3] In these materials, the information can effectively be written
optically and returned to the original state by stimulation of an external field, such as heat, lightillumination, or mechanical stress.[4] Organic photochromic materials (i.e., azobenzenes,[5]spiropyrans,[6] naphthopyrans,[7] and diarylethenes[8]) have been widely studied. Compared withorganic photochromic counterparts, controllable macroscopic shape molding, chemical fatigue
resistance, high thermal stability and mechanical strength of inorganic photochromic materials
can enhance their applicability. To date, a series of inorganic photochromic materials have been
extensively explored, including transition metal oxides (WO3,[9] TiO2[10] and MoO3[11]),ferroelectric ceramics (Na0.5Bi2.5Nb2O9,[12] Na0.5Bi0.5TiO3[13] and K0.5Na0.5NbO3[14]) and robustoxides (BaMgSiO4,[15] PbWO4:Yb3+, Er3+,[16] and Sr2SnO4[17])). Taking advantage of theirphotochromism and reversible luminescence modulation properties, these materials could be
used in optical data storage applications. Persistent Luminescence (PersL) materials andthermoluminescence materials also belong to another specific member of the family applied in
optical information storage devices.[18] PersL materials can store the photon energy under
exposure of short-wavelength electromagnetic waves, and last luminescence for a long timeafter ceasing the excitation light source. Traps are responsible for the photon storage (trapping)and release (detrapping) in the PersL materials. Also, the probability of charge carries
detrapping are largely affected by the trap depth and activation energy. The well-known greenemitting SrAl2O4: Eu, Dy PersL phosphor was described by Matsuzawa et al in the literature in2

1996, which possesses large amounts of traps with 0.5-0.8 eV depth and is applied in nightvision security signs.[19]Since then, many new PersL phosphors with emissions spanning from the ultraviolet (UV)
to the near-infrared (NIR) have been developed. In terms of green or blue PersL phosphors,[20]

these materials show intense luminescence and long PersL duration time (more than 10h),while reports on high-performance PersL phosphors with red emission at 600-650 nm are so far
still scarce in the literature. For this reason, one of the main topics of research in this area
involves improving these red PersL properties through the implementation of activating ions.
Phosphors such as Y2O2S: Eu3+, Mg2+, Ti4+[21] and CaS: Eu2+, Tm3+[22] exhibit the red PersL,
however, they have poor chemical stability and a relatively short PersL duration time. Within
the last few years, other phosphors such as Sr3SiO5: Eu2+, Dy3+,[23] Ca2Sr2Si5N8: Eu2+,[24]CaAlSiN3: Eu2+,[25] and Ca3Ti2O7: Pr3+[26] have been reported, while the duration time was still
not so long. Besides, in most cases, the occurrence of PersL requires high excitation energy,
usually UV light from mercury lamps or xenon arc lamps. For wide applications, it is desirable
to use low-energy photons to achieve effective charging. Up-conversion charging can be a more
promising way to promote the luminescence ion system to a high-energy delocalized state by
low energy photon excitation, followed by filling traps in the materials.[27] Pan et al. reported
that Cr3+ doped Zn3Ga2GeO8 compound was added with the Er3+-Yb3+ up-conversion ion pair.
The combination of up-conversion charging and PersL can overcome the drawbacks in the bioimaging field application.[28] Also, instead of commonly opaque PersL phosphors such as pellet
or powder, transparent ceramic phosphors with high density and optical transparency performed
stronger PersL because they can be illuminated within the whole body, which induces thecarrier formation inside the sample by taking the advantages of lower optical scattering
coefficient.[29]To date, phosphors showing both photochromism and PersL have been reported following
the strong demand for novel smart optical storage materials, however, these materials are3opaque and commonly charged by high energy light.[30] Herein, we aim at developing a novel
multifunctional transparent ceramic which should fulfill the following criteria: (1) hightransparency (2) red PersL and long duration time (3) low energy blue light excitation via upconversion charging (4) reversible photochromism property. Firstly, optical transparent
ceramics generally need to have an isotropic lattice structure (such as a cubic structure). Garnet
structure represented by the most famous Y3Al5O12 (YAG) host in the form of A3[B]2(C)3O12
is belonging to the cubic crystal system with a space group of Ia3d. Three cation sites A, [B],and (C) represent cations that occupy the dodecahedral, octahedral, and tetrahedral sites,
respectively. We reported a series of novel garnet persistent phosphors with a host of Y3Al5xGaxO12 co-doped with rare earth luminescent ions or transition metal ions, especially for thetransparent ceramic phosphor with the composition of Y3Al2Ga3O12 (YAGG): Ce3+ (0.2%)Yb3+(0.1%), which exhibits the PersL for over 138.8 h.[29] Thus, YAGG can be served as an
excellent candidate for PersL. Secondly, a suitable trap for all commercial PersL phosphors is
a vital condition to obtain high PersL performance. Dorenbos proposed vacuum referredbinding energy (VRBE) diagrams and it was successfully applied to predict the energy levelsof lanthanide ions in many materials.[31] With the knowledge of the VRBE diagram of the
YAGG (Ga = 3) host (energy level), we assume that Pr3+ is the most effective ion for achieving
red PersL and can be charged by the up-conversion process due to the following attributes: (1)the 3P0 or 1D2 level of Pr3+ may play the role of an intermediate state in the up-conversion
charging process.[32] (2) the ground state of Pr3+ (3H4) is located above the top of the valenceband (VB) with 1.78 eV large energy gaps, giving rise to a stable recombination center. (3) red
emission from the 1D2 energy level. Considering the innate advantages of Pr3+, we chose Pr3+
as the appropriate activator.
As expected, we successfully developed a multifunctional transparent ceramic phosphor of
Pr3+-doped Y3Al2Ga3O12 with in-line transmittance over 80% at 1800 nm for the first time. The
phosphor exhibits both photochromism and strong red persistent luminescence after several
4

minutes UV light charging or blue light up-conversion charging. The color of the sample
changes to reddish after UV/blue light irradiation and can be recovered by heat treatment. The
sample displays strong red PersL and a long luminance duration time of more than 7 h by 5 min
UV light charging. Employing a series of optical characterizations combined with the electron
spin resonance measurement, its photochromism property, long PersL property, and trappingdetrapping mechanism can be investigated.
2. Results and Discussion
2.1 Photoluminescence Properties of YAGG: Pr3+ Transparent Ceramic

Figure 1. a) PLE spectrum and b) PL spectra of the YAGG: Pr3+ transparent ceramic under 280
and 450 nm light excitation. c) Up-conversion Photoluminescence (UCPL) spectra of the
YAGG: Pr3+ transparent ceramic under various pump power densities from 20.9 to 52.2 W cm2
of 450 nm laser excitation. d) Log-Log scale of UCPL intensities monitoring 309 and 368 nm
vs. pumping power density.
Figure 1a presents the photoluminescence excitation (PLE) spectrum of the YAGG: Pr3+transparent ceramic sample monitoring the 1D2 → 3H4 emission at 636nm. The broad band
located in the UV spectral region with a maximum peak at 280 nm corresponds to the transition
5

from the 3H4 ground state to the lowest 5d1 level of Pr3+. The several narrow peaks located in
the spectral range of 400-500 nm and 560-630 nm are assigned to the 3PJ ← 3H4, 1D2 ← 3H4
transitions, respectively. The normalized emission spectra under different excitation
wavelengths (λex = 280 and 450 nm) of YAGG: Pr3+ transparent ceramic are presented in Figure
1b. When the sample is excited by 280 nm light, two strong emission bands distributed in the
UV spectral region with the maxima at 312 nm and 368 nm are ascribed to the broad, parity
allowed 4f15d1 → 4f2 interconfigurational transitions of Pr3+ ion. Several relatively 4f-4ftransition emission peaks at 487, 533, 562, 660, 714, 745, 827, and 932 nm can be attributed to
3P0 → 3H4, 3P1 → 3H5, 3P0 → 3H5, 3P0 → 3F2, 3P0 → 3F3, 3P0 → 3F4, 1D2 → 3H6, and 3P0 →1G4

transitions, respectively. In addition, the emission peak from 607 to 617 nm derives from theoverlap of 3P0 → 3H6 and 1D2 → 3H4 transitions. Under the excitation of 450 nm (into 3P2), theemission spectrum of the sample is shown in Figure 1b (blue line). Emissions originated from3

P0 level (peak at 487, 562, 617, 660, 714, 745, and 932 nm) are enhanced compared withexcitation of 280 nm. Apart from the spectra lines in the visible region due to 4f-4f transitions,
two UV emission bands from 300 nm to 430 nm also can be obtained. In the case of 280 nm
excitation, the occurrence of the broad UV emission indicates that the lowest energy componentof the 4f15d1 configuration is located below the 1S0 state of Pr3+. It is worth noting that the main
contribution to the 4f-4f emission is from the 1D2 state to the ground state of the Pr3+ ions andthe energy allocated to the 3PJ state is not dominant. Upon excitation with 450 nm, the relative
intensity of emission originated from the 3P0 level becomes stronger. As is known, the 3P0 levelcan be depopulated non-radiatively through a 3P0 → 1D2 multiphonon relaxation process and/or
through cross relaxation process. The energy gap between the 3P0 and 1D2 levels is around 33003400 cm-1, and the phonon energy of YAGG is similar to 820 cm-1 of Y3Al5O12 (YAG). Thus,
at least four high energy phonons are required to bridge the gap between the 3P0 and 1D2
levels.[33] Concurrently, the cross relaxation is suppressed by a lower concentration of the Pr3+
6

ion. Therefore, PL spectrum shows a quite intense emission from 3P0 state under 450 nm
excitation (upon 3PJ state), while 280 nm excitation (upon 4f15d1 state) has a direct sensitization
process to 1D2 level, which may be caused by a low-lying 4f5d configuration of Pr3+.[34]To clarify the up-conversion process involved in UV emission under blue light excitation,
the dependence of the emission intensity on the pump power density of 450 nm CW laser
varying from 20.9-52.2 W cm-2 is investigated in Figure 1c. The number of photons required topopulate the upper emitting levels can be well obtained by the following equation:
𝐼𝐼𝑈𝑈𝑈𝑈 𝛼𝛼 𝑃𝑃𝑛𝑛(1)where 𝐼𝐼 𝑈𝑈𝑈𝑈 is the up-conversion emission intensity, P is the pump power of excitation light, andn is approximately equal to the number of pump photons required to the upper emitting levels.
Figure 1d displays a plot of pump power versus emission intensity in double logarithmic scales.
The slopes n for 309 and 368 nm from 4f15d1 emission are estimated to be 1.69 and 1.78,
suggesting that the UV emissions are two-photon excitation processes. The up-conversion
emission in the UV region may be due to the excited state absorption (ESA) of Pr3+ ion. [35] The
Pr3+ ion may first be excited to 3P2 level using intense blue light and then relaxes rapidly to anintermediate state (i.e., 3P0). The intermediate-state electron may be further promoted to the Pr3+
4f15d1 level and emit UV light. Meanwhile, the pump power density dependence of PL spectrain the 470 to 1000 nm region, and the Log-Log scale of PL intensities monitoring 487 (from 3P0
state) and 607 nm (from 1D2 state) are shown in Figure S1a and S1b (Supporting information),

the slope n for the emission at 487 and 617 nm are 0.82, indicating a linear dependence on thelaser intensity.
2.2 Photochromism in YAGG: Pr3+ Transparent Ceramic

7

Figure 2. a) Photographs of the YAGG: Pr3+ transparent ceramic sample before (upper) andafter (middle) UV(λex = 254 nm) light charging for 15 min. The bottom photograph of thesample shows decoloration after ceasing the UV light after 3 weeks. b) Variation of in-line
transmittance spectra of as-made YAGG: Pr3+ transparent ceramic during the charging processby 254 nm mercury lamp with different charging times. c) Difference of absorption coefficient(Δα) spectra after and before UV charging. d) Time-dependence of Δα spectra after ceasing UVlight with different duration time. e) Time-dependence of Δα monitoring at 321 and 478 nm in
log-log scale.
A worth noticing phenomenon was the fascinating photochromism of the YAGG: Pr3+transparent ceramic. The greenish color of the sample has turned to reddish color after
excitation by the UV light. This photochromism phenomenon was investigated by recording
the in-line transmittance spectra of the YAGG: Pr3+ transparent ceramic before and after 254
nm UV light charging, as shown in Figure 2a. The as-made sample exhibits high transparency,
which is over 80% transmittance at 1800 nm. For the as-made sample without UV charging, astrong absorption band appears in the range of 230-350 nm, which is attributed to the 5d ← 4f
transition of the Pr3+ ions. Several sharp absorption lines in the visible region are ascribed to the3

PJ, 1I6 ← 3H4 (420-500 nm), and 1D2 ← 3H4 (580-630 nm) transitions, respectively. The sharp

absorption lines in the NIR region at around 1300 nm are assigned to the transitions from 3H4
8

to 3F3,4 of Pr3+. With continuing to charge the sample with UV light, additional intense
absorption bands in the UV/visible spectral regions can be observed, resulting in the reddish
color change of the YAGG: Pr3+ transparent ceramic. In addition, the absorption intensity
became stronger with increasing charging time. The absorption band of the photochromic center
was found to be broad in the visible range. To further clarify the photochromism phenomenon
in the sample, the absorption coefficient of the sample has been presented as a function of
wavelength using the equation:
𝛼𝛼 =

1
1
ln � �
𝑑𝑑
𝑇𝑇(2)where d is the thickness of the sample and T is the transmittance. The absorption coefficient
spectra of the sample before and after UV charging are shown in Figure S2 (Supporting
Information). Figure 2c presents the difference of absorption coefficient spectra (Δα = αafter αbefore), which can be used to monitor the absorption of photochromic centers. The Δα spectrum
shows a broad absorption tail in the UV/visible range with two apparent band peaks around 321
and 478 nm responsible for the color change of the sample (deconvolution with Gaussianfunction of the Δα spectrum is provided in Figure S3 (Supporting Information)). To avoid theformation of photochromic centers from other aspects, non-doped sample were fabricated tocompare. The in-line transmittance spectra of non-doped YAGG transparent ceramic before
and after UV light charging are supplemented in Figure S4a (Supporting Information). For theas-made non-doped sample, no absorption peaks appear in the visible region of the spectrum.
However, strong absorption bands in the UV/visible region can be observed after 5 min UV
light charging. Comparing with the Pr3+-doped and non-doped YAGG transparent ceramics ofΔα spectra, similar absorption bands prove that the photochromic centers exist in the YAGG
lattice (Figure S4b, Supporting Information). The time-dependence of Δα measurements after
UV light stoppage was used to reveal variations within detrapping process. Figure 2d presents
the evolution of Δα converted by transmittance (Figure S5, Supporting Information) after UV
9charging for 5 min as a function of duration time at room temperature. With increasing theduration time from 1 min to 3 weeks, the intensity of Δα decreases. In the detrapping process,the colored sample gradually recovers to its initial state at room temperature. It is worth notingthat the Δα spectrum still shows a broad absorption tail in the UV/visible range when the
duration time is 3 weeks, and the bottom photograph of the sample in Figure 2a also candemonstrate this result. Additionally, to clarify the photochromic centers created after UV
irradiation, time-dependence of Δα monitoring at 321 and 478 nm in the Log-Log scale areshown in Figure 2e. Although the intensities of Δα of two photochromic centers decrease withincreasing duration time, two absorption decay curves within the detrapping process show adifferent tendency. For the absorption decay curve of the photochromic center at 321 nm, theslope gives a much more gentle tendency compared with the photochromic center peak at 478
nm. The results suggest two photochromic centers exist, which have different trap depths.
The coloration contrast is also an essential parameter for photochromic materials, which canbe presented by the transmittance contrast degree (ΔRt).[36] The ΔRt of the YAGG: Pr3+transparent ceramic located at 321 nm is expressed by the formula:
𝑇𝑇 −𝑇𝑇

𝛥𝛥𝛥𝛥𝑡𝑡 = 0𝑇𝑇 𝑖𝑖 × 100%(3)0where the T0 is the initial transmittance of as-made sample and the Ti is the transmittance of thesample illuminated for different charging times with UV light. As the charging time increased
from 1 to 3, 5, 10 and 15 minutes, the calculated ΔRt reached 63.4%, 72.5%, 80.0%, 80.2 %and 80.5%, respectively. A saturated transmittance contrast degree of 80% was obtained after
UV light charging for 5 min. Compared with previous transparent inorganic multifunctional
materials,[30] the remarkably large coloration contrast in the YAGG: Pr3+ transparent ceramic
exhibits remarkable photochromic property.
This photochromism induces an increase in the material absorption in the UV/visible range.
An evolution of the PL emission intensity can therefore be expected. Figure S6 (Supporting10

Information) presents the evolution of the PL spectra before and after UV charging withdifferent excitation time. As increasing the charging time, a rise of the PL intensity of 1D2 →3H4 emission (607 nm) is observed, however, the emission from 3PJ luminescence appears to

become weak gradually (from 2 min). After 5 min charging, 3P0 → 3H4 emission (487 nm)
attenuation is reached with a loss of about 15% of the initial intensity; 1D2 → 3H4 emission (607nm) is increased by 2 times of the initial intensity. This decrease in the PL intensity is
unexpected in PersL materials, in which a gradual increase in the PL emission with time is more
likely to occur.[36] Thus, this decrease in PL intensity of 3PJ emission is possibly linked to thephotochromic center, through which the energy transfer from the 3P0 to 1D2 may exist as well.

Figure 3. a) Variation of Δα spectra of as-made YAGG: Pr3+ transparent ceramic during
detrapping process from 300K to 650K with a heating rate of 5K min-1. b) Integrated absorption
intensity of Δα monitoring at 321 and 478 nm from spectra in figure 3a per 10K at each point
as a function of temperature (300-650 K). c) in-line transmittance of the sample at 550 nm byalternating between UV irradiation and heating at 300℃ for 5 min as a function of cycle
numbers.

11

In-situ temperature-dependence of Δα can be a good indicator to discuss the thermallydetrapping behavior of the YAGG: Pr3+ transparent ceramic. Δα spectra against the temperature
within the detrapping process are shown in Figure 3a (Δα = αT – α0). Here, αT is the absorption
coefficient at certain temperature (T) and α0 is the absorption coefficient of the alreadydetrapped sample at 650K. In this measurement, Xe lamp act as the charging light source as
well. The in-situ transmittance spectra of the YAGG: Pr3+ sample during charging process andheating process are shown in Figure S7a and S7b (Supporting Information), respectively. For
the charging process, the absorption coefficient was plotted as a function of charging time
(Figure S7c, Supporting Information). After the absorption intensity became saturated during
Xe lamp charging at room temperature, the sample was heated from 300K to 650K with aheating rate of 5K min-1. The integrated absorption intensity deconvoluted from Δα spectra per
10K monitoring photochromic center at 321 and 478 nm were plotted as a function oftemperature in Figure 3b. With the rise in temperature, the absorption intensities of two
photochromic centers decrease gradually. However, the absorption of photochromic center at
478 nm almost disappeared when the temperature reaches above 510K, while the absorption of
the photochromic center at 321 nm can remain until the temperature upon 600K. Besides, thefirst derivative of absorption plot against the temperature is presented in Figure S8 (Supporting
Information). The inconsistent response against temperature arising from two photochromic
centers indicates that two photochromic centers have different trap depths. The photochromic
center at 321 nm corresponds to much deeper traps compared with another photochromic center.
All the results confirmed that two photochromic centers have distinct detrapping behavior
during the heating process. Thus, it can be concluded that the UV charging induced coloration
can be derived from the formation of two photochromic centers, which can serve as relatively
shallow and deep electron traps to store excitation energy during the charging process. Besides,
when the color sample was heated up to 300℃, the trapped electrons can acquire enough energy
12to escape from the traps and return to their initial stages, and the sample recovers to greenish
transparent state.
It is known that photochromism is generally a reversible photoinduced transformation
process by light irradiation or thermal stimulus. To study the reversibility of coloration anddecoloration, in-line transmittance at 550 nm of the sample after alternative 254 nm UV lightirradiation for 5 min at room temperature and heating at 300℃ for several cycles are shown in
Figure 3c. The sample exhibits robust fatigue resistance due to reversible photoinduced
transformation process by UV light charging and thermal stimulus, which enhances the great
potential of the YAGG: Pr3+ transparent ceramic for optical storage applications.
2.3 Long PersL Properties of YAGG: Pr3+ Transparent Ceramic
PersL materials are typically excited by high-energy UV light and emit visible and infrared
afterglow. In the present work, long PersL of YAGG: Pr3+ transparent ceramic can be obtainedby either UV light charging or blue light through the up-conversion charging process. Afterceasing the 280/450 nm irradiation, the corresponding PersL spectra of the as-made sample atroom temperature were recorded as shown in Figure 4a and b. The normalized spectra wererecorded at 10s after shutting off the light source as presented in Figure 4c, and the insert
photograph exhibits the sample with red PersL after UV irradiation for 5 min. PersL spectra
under UV/blue light irradiation show the characteristic emission peaks of Pr3+ ions, and strong
red PersL in 600-650 nm region because of the Pr3+: 1D2 → 3H4 transition. Additionally, thePersL spectrum under 450 nm irradiation exhibits a nearly identical shape as the PersL spectrum(λirrad. = 280 nm), indicating that the trapping process of PersL is realized via up-conversion
charging. The schematic energy level diagram in Figure 7 elucidates the mechanism of PersL
via up-conversion charging process. By intense blue light excitaion, the system was first excited
to 3P2 level of Pr3+ ion and fast non-radiative relaxation to the 3P0 excited state. The highpumping intensity of the laser diode enables the population of the 3P0 excited state to be highenough to produce substantial excited state absorption. Such an excited 3P0 state can13successively absorb another blue light photon to further pump the system to the delocalizedstate, and fulfill the up-conversion charging process. Subsequently, the electrons could be
detrapped by thermal energy at ambient temperature and cause the PersL. However, it should
be noted that few or no PersL in the UV range under both two different excitation light source.
The reason of lack of UV PersL is mainly due to the photochromic center and the electron traps
in the sample. As mentioned above, the absorption band of the photochromic center was foundto be broad in the UV/visible range after charging. There may be two possibilities: one is theenergy transfer from Pr3+ 5d level to the photochromic center due to the overlapping with 5d4f emission and photochromic absorption; the other is the electron transfer process from 5dlevel to electron traps through the tunnelling process.[37]A key parameter evaluating the PersL performance is the luminance duration time after
ceasing the light source at room temperature. The PersL decay curve (in luminance units) in the
Log-Log scale of the sample by UV/450 nm irradiation for 5 min, is shown in Figure 4d. The
strong red PersL of the sample can be detectable by human eyes in a dark room under either
UV or blue light irradiation. The two PersL decay curves visualize identical slopes whichcorrespond to the PersL decay rate demonstrating the same detrapping process via different
charging light sources. The luminance duration time can last for approximately 27483s (7.63h)
before it drops to 0.32 mcd m-2 (a value commonly used in the safety signage industry, defined
as about 100 times higher than the limit of human eye sensitivity) by 5 min UV light charging.

14

Figure 4. a) PersL spectra after ceasing light source under 280 nm and b) 450 nm lightirradiation for 5 min. c) Normalized PersL spectra at 10s after ceasing the light source. d)Luminance decay curves after UV/blue light irradiation for 5 minutes.
It is recognized that both photochromism and PersL are owing to the presence of defects ininorganic materials. Thermoluminescence (TL) is caused by the thermally detrapping of carriers
that were previously trapped by defects followed by recombination on a luminescent center. TL
is extremely sensitive to defects in the material and can therefore be a powerful tool toinvestigate the trap depth which is determined by the energy difference between the energy
level of the trap and the conduction band.[38] Thus, knowing the trap depth is crucial tounderstand the mechanism of PersL. By measuring the TL intensity as a function of temperature
at a constant heating rate, the TL glow curve can be obtained. The thermal quenching of Pr3+4f-4f luminescence was firstly measured by temperature dependence of PL intensity (Figure S9,
Supporting Information). The PL intensity for the Pr3+ 4f-4f luminescence becomes 63.3% athigh temperature (600K) with respect to the PL intensity at 300K. Figure 5a presents the TL
glow curve of the YAGG: Pr3+ transparent ceramic with a heating rate of 10 K min-1 (calibrated15

by the temperature dependence of PL intensity). The TL glow curve shows two intense peaks
located at 387 K and 522 K (fitted by Gussian function). Two peaks originated from the intrinsic
defects corresponding to the signature of electrons released from the traps. The trap depth canbe estimated by the well-known first-order kinetics presented by Randall and Wilkins: [39]
𝛽𝛽𝛽𝛽
𝜀𝜀
�−
�
=
𝑠𝑠
×
exp
𝑘𝑘𝑇𝑇𝑚𝑚2
𝑘𝑘𝑇𝑇𝑚𝑚(4)

where β is the heating rate (K min-1), k is the Boltzman constant (eV K-1), ε is the trap depth, sis the frequency factor (s-1) and Tm is the TL glow curve peak temperature (K). Because thefrequency factor depends on the host material other than the dopants, the frequency factor of
YAGG: Pr3+ transparent ceramic can be assumed to be 1.0 × 1013 s-1 of the YAGG (x = 3.0):

Ce3+-Cr3+ sample.[31] Then the trap depth values of two peaks can be estimated from the TL

glow curve at 10K min-1 heating rate, which are 1.15 and 1.54eV. Additionally, it is consideredthat the TL glow curve correlates with the temperature dependence of absorption intensity of
two photochromic centers.[40] The first temperature derivative of Δα could be proportional tothe detrapped electrons with increasing the temperature. Figure S8 (Supporting Information)
presents that the first derivative of Δα of two photochromic centers are similar to TL glow curve.
The results further proved that the electron traps of TL and photochromism are identical.
Additionally, the trap depths in the phosphor are much larger than the empirical value of 0.50.8 eV reported in conventional room temperature PersL phosphors,[27] which suggests that the
YAGG: Pr3+ transparent ceramic is suitable for the optical storage application because of a large
number of deep traps to store the recorded data. The TL 2D contour plot of the YAGG: Pr3+transparent ceramic as a function of wavelength and temperature is also essential to further
clarify the contributing emission bands to the TL glow curve, as shown in Figure 5b. The
photograph of the sample in the upper-right presents bright reddish TL under 387K. From thecontour plot of the sample recorded by the Si CCD, TL emission spectra under 387 and 522K
are composed of Pr3+ luminescence center, the peak at 607 nm originates from the Pr3+: 1D2 →16

3H4 emission, and the weak Pr3+: 3P0 → 3H4 luminescence at around 487 nm is also observed.

Both two TL emission spectra show good agreement with the PersL spectra in Figure 4,
indicating that the TL and PersL are related to the electron detrapped from the trap centers.

Figure 5. a) TL glow curve of the YAGG: Pr3+ transparent ceramic with a heating rate of 10 K
min-1. The sample was irradiated by UV light (250 to 380 nm) from a mercury lamp for 5 min.
b) Wavelength−temperature (λ-T) 2D TL contour mapping of the YAGG: Pr3+ transparent
ceramic. The right projection shows the TL emission spectrum at 387 and 522K.
2.4 Electron Spin Resonance Study of Trap Centers
Electron spin resonance (ESR) is a common method to identify the trap centers for many
photochromic and PersL materials.[41] ESR is based on the fact that atoms with an odd numberof electrons exhibit characteristic magnetic properties, and it has proven to be a useful tool for
identifying defect structures and doping ions. Since the YAGG: Pr3+ transparent ceramic wassintered in vacuum atmosphere, we assumed that oxygen vacancies can act as trap centers since
oxygen vacancies 𝑉𝑉𝑂𝑂∙∙ usually exist in the phosphors synthesized under vacuum or reducing

atmosphere. As proof, we measured the ESR spectra before and after UV irradiation (Figure6a). In the case of the as-made sample without UV irradiation, the ESR spectrum shows no

signal. However, the ESR spectrum shows a signal in the 322-357 mT magnetic field range
after UV irradiation for 5min, corresponding to g-factors in the 2.05 to 1.85 range. The ESR
signal shows an asymmetric line which can be fitted by Gaussian function in Figure 6b withtwo main peak signals of g1 = 1.998 and g2 = 1.930. Two g values suggest that at least two kindsof electron traps exist. The g value mainly originated from ionized oxygen vacancy in garnet.[42]17It is probably attributed to the different magnetically inequivalent positions of the oxygen
vacancies in the garnet lattice. Similar results caused by oxygen vacancies have been reported
previously.[43] These magnetically inequivalent positions correspond to distinct directions of
the Al(IV)–VO–Al(VI) chains (paths) in the unit cell. Moreover, it is commonly accepted thatthe oxygen vacancy-based photochromic centers are typical defects in aluminum garnets,
because of the inert or even vacuum atmosphere used during sintering. Defects of oxygen
vacancies in the sample binding free electrons lead to a significant ESR signal after UV lightirradiation. Therefore, it is proved that large numbers of oxygen defects 𝑉𝑉𝑂𝑂∙∙ were introduced in

the YAGG: Pr3+ transparent ceramic, which is major for the photochromism and PersL

properties.

Figure 6. a) ESR spectra of YAGG: Pr3+ transparent ceramic before (black) and after 5 min
UV irradiation (red) in the X band at room temperature. b) Decomposition of the ESR line after
UV irradiation into two Gaussian components demonstrating anisotropy of the g factor.
3. Photochromism and Persistent Luminescence Mechanism
Based on the results above, we may elucidate the photochromism and PersL mechanism byusing the VRBE energy diagram of YAGG along with the charging and detrapping process as
illustrated in Figure 7. Firstly, the 4f ground state electrons of Pr3+ are excited into the
conduction band under UV/blue light irradiation through the 5d levels, followed by being
trapped subsequently by the electron trap centers of intrinsic defects-oxygen vacancies 𝑉𝑉𝑂𝑂∙∙ . The

reversible conversion between 𝑉𝑉𝑂𝑂∙∙ and 𝑉𝑉𝑂𝑂∙ by trapping and releasing an electron corresponding18

to both the shallow traps and deep traps causes photochromism. Besides, the trapped electrons
also can be detrapped slowly from shallow traps to recombine center without external excitation
at room temperature owing to thermal vibration, which is responsible for the persistentluminescence. The creation of trapping centers may be caused in the following way. Oxygen
vacancies 𝑉𝑉𝑂𝑂∙∙ usually exist in the phosphors synthesized under vacuum or reducing atmosphere.

The presence of intrinsic defects-oxygen vacancies for photochromism causes the reversible
conversions between 𝑉𝑉𝑂𝑂∙∙ and 𝑉𝑉𝑂𝑂∙ by trapping and releasing an electron. In addition, Ga
volatilization can be easily formed during the high temperature sintering process. We propose,,,that 𝑉𝑉𝐺𝐺𝐺𝐺
could be responsible for the negative effective charge defects, which are generated forthe charge compensation.

Figure 7. VRBE energy levels and schematic illustration of charging and detrapping
electrons in YAGG: Pr3+ transparent ceramic.
4. Toward Optical Storage Applications
The optical storage applications based on photochromic and PersL phosphors were extensively
reported.[44] The schematic illustration of the write-in and read-out, erasing and rewriting byaltering between UV/blue light irradiation and thermal bleaching at 300℃ is shown in Figure
8a. As an example, the information display in YAGG: Pr3+ transparent ceramic is presented in
Figure 7b. The sample covered by mask A was irradiated using a 254 nm mercury lamp. After19the information write-in by 5 min UV irradiation, the reddish patterns of the mask weredisplayed based on the photochromic behavior in the light room. Benefit from the hightransmittance of the sample, reddish patterns not only on the surface but inside the body of thesample after irradiation. For the dark field, the write-in information can be read out by TL
because of deep trap depth, as discussed above. The forming information can be bleached upon
thermal stimulus. The recovered sample also can be reused many times with different masks(Mask B and Mask C), which enhances the potential applicability for the optical storage field.
Notably, the information can remain for more than 3 weeks as shown in Figure 2. Furthermore,
optical information write-in can also be realized by up-conversion charging using a 450 nm
laser. One can see remarkable signal augment with increasing laser irradiation times in Figure
8b. As a consequence, the better optical data retention ability and optional irradiation lightsource by either UV or blue light endow the YAGG: Pr3+ transparent ceramic with potential
feasibility in various optical storage applications.

20

Figure 8. a) Schematic illustration of the write-in and read-out of optical information. b)
Optical information display of write-in, read-out and bleaching based on photochromism(PC) and PersL in YAGG: Pr3+ transparent ceramic by altering between 254 nm
irradiation and 300℃ thermal stimulus. c) Demonstration experiment for opticalinformation storage in the YAGG: Pr3+ transparent ceramic by increasing 450 nm laser
irradiation times, showing the mode of up-conversion write-in and read-out withcorresponding PersL 30s after ceasing the light source.
5. Conclusion
In summary, a multifunctional transparent ceramic phosphor by doping Pr3+ into Y3Al2Ga3O12,
aiming at obtaining novel optical information storage material, has been successfully
synthesized for the first time. The phosphor exhibits both photochromism and strong red
persistent luminescence after several minutes UV light charging or blue light up-conversion
charging. The reversibility of greenish-reddish color change by alternating UV/blue lightirradiation and thermal stimulus, demostrates excellent fatigue resistance. In the case of UV
irradiation, the luminance can last for 27483s (7.63h) before it drops to 0.32 mcd/m2,
additionally, the reddish color can remain for more than three weeks. Two trap centers of
intrinsic defects-oxygen vacancies 𝑉𝑉𝑂𝑂∙∙ with different trap depths were deeply studied with theassistance of in-situ time dependence and temperature dependence of Δα, TL, and ESR. By
using the VRBE energy diagram, the mechanism of photochromism and PersL has been
elucidated and discussed comprehensively. The study of YAGG: Pr3+ transparent ceramic gives
researchers an insight into the nature of traps involved in photochromism and PersL, and offers
an opportunity for designing novel multifunctional materials applied in the optical information
storage fields.
6. Experimental Section
Sample Preparation: Polycrystalline ceramics of Y3Al2Ga3O12 and Y3Al2Ga3O12: Pr3+ (0.1%)
were synthesized using solid-state reactions. The chemicals Y2O3 (99.99%), Al2O3 (99.99%),
Ga2O3 (99.99%), and Pr6O11 (99.99%) were used as the starting materials. The powders weremixed by ball milling (Fritsch, Premium Line P-7) with ethanol. The obtained slurry was driedin an oven for 20 hours to remove the ethanol solvent and pulverized. The powders were pressed21

at 50 MPa into pellets (Ф=20 mm) and then sintered at 1650℃ for 12 h under a vacuum
atmosphere. The obtained transparent ceramics were double-surface polished simultaneously
by using a copper plate and diamond slurry, and the final thickness was 1.3±0.1 mm.
Characterization: The crystalline phases of transparent ceramic samples were identified asgarnet crystals using an X-ray diffraction (XRD) equipment (Ultima IV, Rigaku). The as-madenon-doped and Pr3+-doped samples were confirmed to be single phase without any impurities(Figure S10, Supporting Information). Surface microstructural properties and the distributionof elements in the YAGG: Pr3+ transparent ceramic was characterized using scanning electron
microscopy (SEM, SU8220, HITACHI, Japan) with an X-ray energy detector (EDX, HORIBA,
Japan) system. No other impurity elements in the preparation process of the transparent ceramicin this experiment. The sample presents a fully dense microstructure and homogenous elements
distribution (Figure S11, Supporting Information).
Optical Measurements: Photoluminescence excitation (PLE) spectra were measured with asetup consisting of a Xe lamp (OPM2-502XQ, Ushio Inc.), double monochromators (SP-300i,
Acton Research Corp.), and a photomultiplier tube (R3896, Hamamatsu Photonics). The PLE
spectra were calibrated by the spectrum of the Xe lamp (excitation light source) detected by a
Si standard photodiode (S1337-1010BQ, Bunkoukeiki Co. Ltd.). Photoluminescence (PL) and
PersL spectra of the samples were measured at 300K by a Si CCD spectrometer (QE65-Pro,
Ocean Optics) and calibrated by a standard halogen lamp. An optical parametric oscillator laser(NT342B-20-SH/SF, Ekspla) was used as the excitation source for PL and PersL measurements.
For the up-conversion investigation, the sample set in a cryostat (Helitran LT3, Advanced
Research Systems) at 80 K was pumped by a 450 nm CW laser. The ceramic sample was also
firstly heated up to 750K to empty the trap and cooled down to 80K. The in-line transmittancespectra were measured by a UV-vis-NIR spectrometer (UV-3600, Shimadzu). For the in-situ
transmittance spectra, the measurement setup was composed of a Xe lamp (MAX-302, Asahi
Spectra Co., Ltd, Japan) that acted as the excitation source as well, a CCD spectrometer22

(QE65Pro, Ocean Optics) and thermal stage for the heating process. UV lamp (SP-9, Ushio)
was used as the excitation source for thermoluminescence (TL) two-dimensional (2D) plotmeasurements. The transparent ceramic sample was set in a cryostat (VPF-800, Janis) to control
temperatures and firstly heated up to 750K to empty the trap and cooled down to 80K. The
sample was irradiated by UV light at 80 K for 5 min, then heated up to 650 K at a rate of 10 K
min-1 after ceasing the irradiation. The TL signals were recorded by a PMT detector (R11041,
Hamamatsu Photonics & Co. Ltd.,). The same Si CCD spectrometer was operated
simultaneously with the TL measurement to monitor the TL emission spectra at different
temperatures. The PersL decay curves of the sample were obtained at room temperature withthe same PMT detector as in the TL measurement. The sample was excited for 5 min by the UVlamp (SP-9, Ushio) at UV range of 250-350 nm and by a 450 nm CW laser for up-conversion
charging. Then, the decay curves were converted to luminance (in the unit of mcd m-2) by PersL
Intensity. The PersL spectra of the sample after ceasing the light source were detected by acalibrated CCD spectrometer (GlacierX BTRANSPARENT CERAMIC112E, B&W Tek).
Electron spin resonance (ESR) spectra were measured using JEOL type JES-RE2X X-band
spectrometer at room temperature before and after 254 nm UV lamp irradiation for 5min.
Before irradiation, the sample was detrapped under 350℃ for 5 min.
Optical Information Write-in and Read-out: The multifunctional phosphor was covered by
Mask A, Mask B, and Mask C with specific patterns, and irradiated by UV light (254 nm
mercury lamp) for 5 min. The desired information was recorded after ceasing the UV light andremoving the mask. The recorded data read-out can be realized by TL at target temperature.
Additionally, blue light laser (MASTER 2, NEJE) can be used as write-in light source for
optical data storage on the transparent ceramic as well. The mushroom patterns were engraved
under blue light excitation with different irradiation times.
Supporting Information
Supporting Information is available from the Wiley Online Library or from the author.
23

Acknowledgements
This research was financially supported by JSPS KAKENHI (grant number is 20H02438). Q.
Du acknowledges support from the China Scholarship Council (CSC), China, and the Ministryof Education, Culture, Sports, Science and Technology (MEXT), Japan for a scholarship grant.
Received: ((will be filled in by the editorial staff))
Revised: ((will be filled in by the editorial staff))
Published online: ((will be filled in by the editorial staff))
References[1] a) M. Hilbert, P. Lopez, Science 2011, 332, 60; b) M. Gu, X. Li, Y. Cao, Light-Sci. Appl.
2014, 3, 11.
[2] a) D. A. Parthenopoulos, P. M. Rentzepis, Science 1989, 245, 843; b) J. Zhang, M.
Gecevicius, M. Beresna, P. G. Kazansky, Phys. Rev. Lett. 2014, 112, 5; c) M. Gu, Q. Zhang, S.
Lamon, Nat. Rev. Mater. 2016, 1, 14; d) D. Liu, L. Yuan, Y. Jin, H. Wu, Y. Lv, G. Xiong, G.
Ju, L. Chen, S. Yang, Y. Hu, ACS Appl. Mater. Interfaces 2019, 11, 35023; e) Z. Hu, X. Huang,
Z. Yang, J. Qiu, Z. Song, J. Zhang, G. Dong, Light-Sci. Appl. 2021, 10, 9.
[3] a) H. Durr, in Photochromism: Molecules And Systems, Vol. 40 (Eds: H. Durr, H.
Bonauslaurent), Elsevier Science Bv, Amsterdam 1990, 1; b) M. Irie, T. Fulcaminato, K.
Matsuda, S. Kobatake, Chem. Rev. 2014, 114, 12174.
[4] a) Y. L. Han, M. Hamada, I. Y. Chang, K. Hyeon-Deuk, Y. Kobori, Y. Kobayashi, J. Am.
Chem. Soc. 2021, 143, 2239; b) K. Fujita, S. Hatano, D. Kato, J. Abe, Org. Lett. 2008, 10, 3105;c) J. Harada, R. Nakajima, K. Ogawa, J. Am. Chem. Soc. 2008, 130, 7085.
[5] G. Jaume, D. Velasco. Beilstein J. Org. Chem. 2012, 8, 1003.
[6] L. A. Frolova, A. A. Rezvanova, B. S. Lukyanov, N. A. Sanina, P. A. Troshin and S. M.
Aldoshin. J. Mater. Chem. C 2015, 3, 11675.
[7] C. M. Sousa, J. Berthet, S. Delbaere, A. Polonia, P. J. Coelho. J. Org. Chem. 2017, 82,
12028.
[8] A. Spangenberg, R. Métivier, J. Gonzalez, K. Nakatani, P. Yu, M. Giraud, A. Léaustic, R.
Guillot, T. Uwada, T. Asahi. Adv. Mater. 2009, 21, 309.
24

[9] J. Wei, X. Jiao, T. Wang, D. Chen, J. Mater. Chem. C 2015, 3, 7597.
[10] D. M. Tobaldi, S. G. Leonardi, R. C. Pullar, M. P. Seabra, G. Neri, J. A. Labrincha, J.
Mater. Chem. A 2016, 4, 9600.
[11] J. N. Yao, K. Hashimoto, A. Fujishima, Nature 1992, 355, 624.
[12] Q. Zhang, H. Sun, H. Li, X. Wang, X. Hao, J. Song, S. An, Chem. Commun. 2015, 51,
16316.
[13] K. Li, L. Luo, Y. Zhang, W. Li, Y. Hou, ACS Appl. Mater. Interfaces 2018, 10, 41525.
[14] H. Wang, J. Lin, B. Deng, T. Lin, C. Lin, Y. Cheng, X. Wu, X. Zheng, X. Yu, J. Mater.
Chem. C 2020, 8, 2343.
[15] M. Akiyama, H. Yamada, K. Sakai, J. Ceram. Soc. Jpn. 2011, 119, 105[16] X. Bai, Z. Yang, Y. Zhan, Z. Hu, Y. Ren, M. Li, Z. Xu, A. Ullah, I. Khan, J. Qiu, Z. Song,
B. Liu, Y. Wang, ACS Appl. Mater. Interfaces 2020, 12, 21936.
[17] Y. Zhang, L. Luo, K. Li, W. Li, Y. Hou, J. Mater. Chem. C 2018, 6, 13148.
[18] a) J. Holsa, Electrochem. Soc. Interface 2009, 18, 42; b) Y. Zhuang, Y. Lv, L. Wang, W.
Chen, T. L. Zhou, T. Takeda, N. Hirosaki, R. J. Xie ACS Appl. Mater. Interfaces 2018, 10,
1854; c) D. Poelman, D. Van der Heggen, J. R. Du, E. Cosaert, P. F. Smet, J. Appl. Phys. 2020,
128, 13.
[19] T. Matsuzawa, Y. Aoki, N. Takeuchi, Y. Murayama, J. Electrochem. Soc. 1996, 143, 2670.
[20] a) P. F. Smet, N. Avci, K. Van den Eeckhout, D. Poelman, Opt. Mater. Express 2012, 2,1306; b) J. Ueda, T. Shinoda, S. Tanabe, Opt. Mater. Express 2013, 3, 787; c) P. Dorenbos,
Phys. Status Solidi B-Basic Solid State Phys. 2005, 242, R7.
[21] Y. Wang, Z. Wang, J. Rare Earths 2006, 24, 25.
[22] D. Jia, W. Jia, D. R. Evans, W. M. Dennis, H. Liu, J. Zhu, W. M. Yen, J. Appl. Phys. 2000,
88, 3402.
[23] T. Aitasalo, A. Hietikko, D. Hreniak, J. Holsa, M. Lastusaari, J. Niittykoski, W. Strek, J.
Alloy. Compd. 2008, 451, 229.
25

[24] K. Van den Eeckhout, P. F. Smet, D. Poelman, J. Lumines. 2009, 129, 1140.
[25] J. Ueda, S. Tanabe, K. Takahashi, T. Takeda, N. Hirosaki, Bull. Chem. Soc. Jpn. 2018, 91,
173.
[26] B. Wang, H. Lin, J. Xu, H. Chen, Z. Lin, F. Huang, Y. Wang, Inorg. Chem. 2015, 54,
11299.
[27] a) Y. Chen, F. Liu, Y. Liang, X. Wang, J. Bi, X. J. Wang, Z. Pan, J. Mater. Chem. C 2018,
6, 8003; b) J. Xu, S. Tanabe, J. Lumines. 2019, 205, 581.
[28] a) F. Liu, Y. Liang, Z. Pan, Phys. Rev. Lett. 2014, 113, 5; b) F. Liu, Y. Chen, Y. Liang, Z.
Pan, Opt. Lett. 2016, 41, 954.
[29] a) J. Xu, J. Ueda, K. Kuroishi, S. Tanabe, Scr. Mater. 2015, 102, 47; b) J. Ueda, S. Miyano,S. Tanabe, ACS Appl. Mater. Interfaces 2018, 10, 20652.
[30] a) K. Asami, J. Ueda, S. Tanabe, J. Lumines. 2019, 207, 246; b) V. Castaing, L. Giordano,
C. Richard, D. Gourier, M. Allix, B. Viana, J. Phys. Chem. C 2021, 125, 10110.
[31] a) P. Dorenbos, J. Mater. Chem. 2012, 22, 22344; b) P. Dorenbos, J. Lumines. 2013, 134,
310; c) J. Xu, J. Ueda, S. Tanabe, J. Mater. Chem. C 2016, 4, 4380; d) J. Ueda, P. Dorenbos,
A. J. J. Bos, K. Kuroishi, S. Tanabe, J. Mater. Chem. C 2015, 3, 5642. e) J. Ueda, Bull. Chem.
Soc. Jpn. 2021, 94, 2807.
[32] a) S. Yan, Q. Gao, X. Zhao, A. Wang, Y. Liu, J. Zhang, X. J. Wang, F. Liu, J. Lumines.
2020, 226, 117427; b) S. Yan, F. Liu, J. Zhang, X. J. Wang, Y. Liu, Phys. Rev. Appl. 2020, 13,8.
[33] a) J. B. Gruber, M. E. Hills, R. M. Macfarlane, C. A. Morrison, G. A. Turner, Chemical
Physics 1989, 134, 241; b) E. Cavalli, L. Esposito, M. Bettinelli, A. Speghini, K. V.
Ivanovskikh, R. B. Hughes-Currie, M. De Jong, Materials Research Express 2014, 1, 045903;c) A. Lukowiak, R. J. Wiglusz, M. Maczka, P. Gluchowski, W. Strek, Chem. Phys. Lett. 2010,
494, 279.
26

[34] a) C. D. Donega, A. Meijerink, G. Blasse, J. Phys. Chem. Solids 1995, 56, 673; b) R.
Naccache, F. Vetrone, A. Speghini, M. Bettinelli, J. A. Capobianco, J. Phys. Chem. C 2008,
112, 7750.
[35] G. Özen, O. Forte, B. Di Bartolo, J. Appl. Phys. 2005, 97, 013510.
[36] H. Zhao, Y. Cun, X. Bai, D. Xiao, J. Qiu, Z. Song, J. Liao, Z. Yang, ACS Energy Lett.
2022, 7, 2060.
[36] a) J. Botterman, J. J. Joos, P. F. Smet. Phys. Rev. B 2014, 90, 085147. b) C. Tydtgat, K. W.
Meert, D. Poelman, P. F. Smet. Opt. Mater. Express 2016, 6, 844.
[37] P, Avouris, T. N. Morgan, J. Chem. Phys. 1981, 74, 4347.
[38] a) J. R. Du, K. L, R. V. D, D. Poelman, H. L, Adv. Opt. Mater. 2022, 10, 2101714; b) J.
Ueda, Bull. Chem. Soc. Jpn. 2021, 94, 2807; c) A. J. J. Bos, Radiat. Meas. 2007, 41, S45; d) Y.
Zhuang, L. Wang, Y. Lv, T. L. Zhou, R. J. Xie, Adv. Funct. Mater. 2018, 28, 1705769.
[39] a) J. T. Randall, M. H. F. Wilkins, Proc. R. Soc. A Math. Phys. Eng. Sci. 1945, 184, 390,12; b) J. T. Randall, M. H. F. Wilkins, Proc. R. Soc. A Math. Phys. Eng. Sci. 1945, 184, 366.
[40] J. Ueda, A. Hashimoto, S. Tanabe, J. Phys. Chem. C 2019, 123, 29946.
[41] a) Y. Ren, Z. Yang, M. Li, J. R, J. Zhao, J. Qiu, Z. Song, D. Zhou, Adv. Opt. Mater. 2019,7, 1900213; b) Y. Han, M. Hamada, I. Y. Chang, H. D. Kim, Y. Kobori, Y. Kobayashi, J. Am.
Chem. Soc. 2021, 143, 2239.
[42] a) K. Mori, physica status solidi (a) 1977, 42, 375; b) M. Nikl, A. Vedda, M. Fasoli, I.
Fontana, V. V. Laguta, E. Mihokova, J. Pejchal, J. Rosa, K. Nejezchleb, Phys. Rev. B 2007, 76,
8.
[43] a) M. Nikl, V. Laguta, A. Vedda, Physica status solidi (b) 2008, 245, 1701; b) V. Laguta,
M. Buryi, P. Arhipov, O. Sidletskiy, O. Laguta, M. Brik, M. Nikl, Phys. Rev. B 2020, 101,
024106.

27

[44] a) Z. Hu, X. Huang, Z. Yang, J. Qiu, Z. Song, J. Zhang, G. Dong, Light Sci. Appl. 2021,
10, 140. b) Z. Yang, J. Hu, L. I. D. J. Martin, D. Van der Heggen, D. Poelman. J. Mater. Chem.
C 2021, 9, 14012.

28

Table of Contents
The developed multifunctional Pr3+-doped Y3Al2Ga3O12 transparent ceramic for opticalstorage application, exhibiting both photochromism and red persistent luminescence with long
luminance duration time of more than 7 h, has been successfully prepared for the first time. The
multifunctional properties can be achieved by either UV light or blue light up-conversion
excitation.

Qiping Du*, Jumpei Ueda*, Ruilin Zheng, and Setsuhisa Tanabe
Photochromism and Long Persistent Luminescence in Pr3+-Doped Garnet Transparent
Ceramic via Ultraviolet or Blue Light Up-conversion Charging
ToC figure29