Role of Eu2+ and Dy3+ Concentration in the Persistent Luminescence of Sr2MgSi2O7 Glass-Ceramics

Ci a ion: Fe nández-Rod íguez, L.;
Balda, R.; Fe nández, J.; Du án, A.;
Pascual, M.J. Role o Eu2+ and Dy3+
Concen a ion in he Pe sis en
Luminescence o S 2MgSi2O7
Glass-Ce amics. Ma e ials 2022,15,
3068. h ps://doi.o g/10.3390/
ma15093068
Academic Edi o : Gianca lo C.
Righini
Recei ed: 30 Ma ch 2022
Accep ed: 21 Ap il 2022
Published: 23 Ap il 2022
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ma e ials
A icle
Role o Eu2+ and Dy3+ Concen a ion in he Pe sis en
Luminescence o S 2MgSi2O7Glass-Ce amics
Lau a Fe nández-Rod íguez 1, Rolindes Balda 2,3 , Joaquín Fe nández 4, Alicia Du án1
and Ma ía Jesús Pascual 1,*
1Ce amics and Glass Ins i u e (CSIC), C/Kelsen 5, Campus de Can oblanco, 28049 Mad id, Spain;
lau a. e nandez@ic .csic.es (L.F.-R.); adu an@ic .csic.es (A.D.)
2Depa amen o Física Aplicada, Escuela Supe io de Ingenie ía, Uni e sidad del País Vasco (UPV-EHU),
48013 Bilbao, Spain; [email p o ec ed]
3Cen o de Física de Ma e iales, UPV/EHU-CSIC, 20018 San Sebas ian, Spain
4Donos ia In e na ional Physics Cen e DIPC, 20018 San Sebas ian, Spain; [email p o ec ed]
*Co espondence: mpascual@ic .csic.es
Abs ac :
In his s udy, glass-ce amics based on S
2
MgSi
2
O
7
phospho co-doped wi h Eu/Dy we e
ob ained om he sin e ing and c ys allisa ion o glass powde s. The glasses we e mel ed in a gas
u nace o simula e an indus ial p ocess, and he dopan concen a ion was a ied o op imise he
luminescence pe sis ence imes. The doped pa en glasses showed ed emission unde UV ligh
exci a ion due o he doping o Eu
3+
ions, while he co esponding glass-ce amics showed pe sis en
blue emission co esponding o he p esence o Eu
2+
in he c ys alline en i onmen . The dopan
concen a ion had a s ong impac on he sin e ing/c ys allisa ion kine ics a ec ing he inal glass-
ce amic mic os uc u e. The mic os uc u es and mo phology o he c ys als esponsible o he blue
emission we e obse ed by scanning elec on mic oscopy–ca hodoluminescence. The composi ion
o he c ys allised phases and he dis ibu ion o a e-ea h (RE) ions in he c ys als and in he
esidual glassy phase we e de e mined by X- ay di ac ion and ene gy dispe si e X- ay analysis.
The emission and pe sis ence o phospho escence we e s udied by pho oluminescence.
Keywo ds: S 2MgSi2O7; phospho s; eu opium; glass-ce amics; pe sis en luminescence
1. In oduc ion
Ra e-ea h (RE)-doped glasses and glass-ce amics a e conside ed good ma ices o
luminescen o ligh -emi ing applica ions. Some o hei well-known applica ions a e
LEDs, sensing, sola cells, biomedicine, e c. [1–4].
A wide a ie y o hos ma e ials a e used as luminescen compounds, bu mos
known hos s decline when i comes o pe sis en luminescence. Fo many decades, coppe -
doped zinc sulphide [
5
] has been he mos widely used pe sis en phospho ; howe e , i s
b igh ness and li e ime we e a he low (<1 min) o p ac ical pu poses. Cu en ly, he use
o ZnS: Cu has dec eased in a ou o a e-ea h-doped alumina es and silica es [6].
Since he mid-1990s, a new gene a ion o pe sis en luminescen phospho s has been
de eloped and has pa ially en e ed he comme cial ma ke [
7
]. Mos esea ch g oups
ocused hei a en ion on s on ium alumina e ma ices doped wi h eu opium and i s
de i a i es S Al
2
O
4
:Eu
2+
, Dy
3+
[
8
]. Eu
2+
-, Dy
3+
-, and Nd
3+
-doped alumina es exhibi
blue-cen ed emission bands [
9
,
10
]. These alumina es ha e a hal -li e close o 6 h [
11
,
12
].
Ano he g oup o ma e ials ha has ecen ly been in es iga ed is silica es. Silica es we e
chosen as hos s due o hei special p ope ies, such as low cos , ease o p epa a ion, and
excellen he mal and chemical s abili ies. The M
2
MgSi
2
O
7
(M = Ca, S , Ba) amily o
ma e ials, also called alkaline ea h ake mani es, plays a simila ole o ha o MAl
2
O
4
in
he alumina e g oup. The bes -known pe sis en luminescen silica e, S
2
MgSi
2
O
7
: Eu
2+
,
Dy
3+
was in es iga ed o he i s ime by Lin e al. in 2001 [
13
]. The emission band is
Ma e ials 2022,15, 3068. h ps://doi.o g/10.3390/ma15093068 h ps://www.mdpi.com/jou nal/ma e ials
Ma e ials 2022,15, 3068 2 o 15
cen ed in he blue and has a hal -li e o abou 10 h when he ma e ial is p oduced by
solid-s a e syn hesis [14].
The solid-s a e eac ion is he mos common way o p epa e c ys alline ma e ials based
on M
2
MgSi
2
O
7
c ys alline ma e ials, bu cop ecipi a ion [
15
] and combus ion [
16
] me hods
ha e also been success ully applied.
In he in es iga ions o Tian e al. [
17
], he concen a ion dependence and ene gy
ans e o Y
2
(MoO
4
)
3
: Dy
3+
ype phospho s we e analysed. The mechanism o ene gy
ans e s be ween Dy
3+
ions was s udied by se e al heo ies, and i was concluded ha he
elec ic dipole–dipole in e ac ion be ween Dy
3+
ions is he main physical mechanism o
ene gy ans e s be ween Dy3+ ions.
Jiang e al. [
18
] syn hesised Ca
2
MgSi
2
O
7
: Eu, Dy, Nd, using he solid-s a e eac ion
me hod, and modi ied he Dy/Eu a io, o obse e he changes in he luminescen esponse.
The emission in ensi y a 518 nm and he decay a e we e di e en o phospho s wi h
di e en Dy/Eu a ios. By sligh ly inc easing he Eu
2+
con en wi h a cons an Dy
3+
and
Nd
3+
con en (Dy/Eu = 1/2 o 1/1), bo h he emission in ensi y and a e glow inc eased.
Howe e , when he alue o Dy/Eu was highe han 20/7, he a e glow ime and emis-
sion in ensi y dec eased, which can be a ibu ed o concen a ion quenching o Eu
2+
.
Ne e heless, no pe sis ence s udies ha e been included in hei esea ch.
Sh i as a a e al. [
19
] p epa ed Ca
2
MgSi
2
O
7
: Eu
2+
, Dy
3+
o di e en Eu/Dy concen-
a ion a ios wi h solid-s a e eac ion. The emission spec a we e iden ical in shape, and
he bands di e ed only in in ensi ies, wi h he highes obse ed o
Eu/Dy a io = 0.5/1.5
.
The b oad emission spec a cen ed a 510 nm we e obse ed unde he ul a iole exci-
a ion o 395 nm, which co espond o Eu
2+
emission. Since he c ys al ield can g ea ly
a ec he elec onic s a es, his sugges s ha he c ys al ield does no change much wi h
composi ional a ia ions. The in ensi y o he he moluminescence signals dec eased, and
he posi ion o he empe a u e peak shi ed o he uppe side wi h inc easing delay ime,
indica ing a easonable e ac ion associa ed wi h non- i s o de kine ics. The decay cu e
showed cha ac e is ics o a simple exponen ial equa ion, wi h a decay cons an o 4.96 min.
He e al. [
20
] success ully p epa ed S
2
MgSi
2
O
7
:Eu
2+
, Dy
3+
nano ibe s using he elec-
ospinning me hod. The S
2
MgSi
2
O
7
:Eu
2+
, Dy
3+
nano ibe s we e o med a e calcining a
1150
◦
C o 5 h. The op imum concen a ion o Eu and Dy co-doping o his in es iga ion
was x = 0.03, y = 0.04 in S
2-x-y
MgSi
2
O
7
:xEu
2+
, yDy
3+
; he nano ibe s had a blue emission
peak a 471 nm, a ibu ed o ypical Eu
2+
emission, which is made om he 4
6
5d
1
-4
7
ansi ion. The co-doped Dy
3+
ion plays an impo an ene gy ans e and elec on ap-
ping ole and can p olong he pe sis ence ime o he luminescen S
2
MgSi
2
O
7
:Eu
2+
, Dy
3+
nano ibe s. Howe e , no da a ega ding decay o pe sis ence imes ha e been p o ided in
his s udy.
Luminescen emissions in glass-ce amic ma e ials a e s ongly a ec ed by c ys allini y,
as well as by mic os uc u e, numbe o ac i e cen es p esen , ma ix composi ion, c ys al
ield, e c.
Wond aczek e al. [
21
] in es iga ed (S ,Ca)–ake mani e (Ca,S )
2
MgSi
2
O
7
glass-ce amics
doped wi h eu opium. The ed emission o he glass p esen ed a cha ac e is ic Eu
3+
band,
while he glass-ce amic emi ed in blue wi h he cha ac e is ic Eu
2+
band. Scanning elec on
mic oscopy–ca hode-luminescence (SEM–CL) cha ac e isa ion indica ed ha he c ys alline
phase was associa ed wi h Eu
2+
emission, and i was claimed ha Eu
2+
is inco po a ed
in he S
2+
si es o he ake mani e s uc u e, while Eu
3+
accumula es in he in e g anula
phase o he glass.
Acco ding o Hölsä’s in es iga ions [
22
] on he mechanism o luminescence, he
exac ole o de ec s in exci a ion ene gy s o age is s ill no well unde s ood. I has been
es ablished ha de ec s can o m due o cha ge compensa ion and p epa a ion condi ions.
The mos signi ican s uc u al modi ica ions due o de ec s in he en i onmen o he Eu
2+
luminescen cen e we e ound wi h he in oduc ion o he s on ium acancy. Elec on
aps we e c ea ed by he Eu
2+
and s on ium acancy, as well as by he oxygen acancy,
while s on ium, magnesium, and silicon acancies also c ea ed shallow oids in he
Ma e ials 2022,15, 3068 3 o 15
ma e ial. Elec on aps close o he conduc ion band may con ibu e o he pe sis en
luminescence e iciency, as hey a e easily bleached by he mal ene gy a oom empe a u e.
Howe e , aps ha a e oo shallow o oo deep can dec ease his e iciency. La e , Duan [
23
]
p oposed ha , o e e y oxygen acancy, he e a e wo associa ed elec ons, and hese
ully occupy he single s a e, which is c ea ed om he alence band s a es o he hos .
Fu he mo e, he gap be ween oxygen and acancy na ows on he o de o 1–2 eV ela i e
o he S
2
MgSi
2
O
7
gap. This means ha he inco po a ion o oxygen acancies can enhance
he pe sis en luminescence o he ma e ial by imp o ing he abso p ion o ul a iole ligh .
Eu
2+
ions ac as luminescen cen es, while Dy
3+
ions ac mainly as aps in he hos [
24
].
The oxygen acancies and Dy
3+
ions p o ide he deep aps; he esidual conduc ion band
elec ons can be apped a e u ning o he UV ligh sou ce. The Dy ions in S
2
MgSi
2
O
7
:
Eu
2+
, Dy
3+
only ac as apping cen es, since S
2
MgSi
2
O
7
: Dy
3+
wi hou Eu doping has no
luminescen p ope ies [25].
As discussed ex ensi ely in a p e ious pape [
26
], glass-ce amics based on Eu/Dy-
doped S
2
MgSi
2
O
7
phospho we e ob ained om sin e ing and c ys allisa ion o glass
powde s (base composi ion 55SiO
2
-27S O-18MgO mol%). Inc easing he dopan con en
esul ed in highe s abili y o he glass agains c ys allisa ion. Elec ic and gas u naces
we e used o glass mel ing. The doped pa en glasses showed ed emission unde UV ligh
exci a ion, while he co esponding glass-ce amics showed blue emission. The emission
spec a o he glass-ce amics indica ed ea u es a ibu able o Eu
2+
and Eu
3+
ca ions. The
Eu/Dy co-doped glass-ce amic p o ided a lowe Eu
3+
associa ed signal han ha o he
Eu-doped glass-ce amic. Ca hodoluminescence measu emen s indica ed ha Eu
2+
emis-
sion o igina ed om S
2
MgSi
2
O
7
c ys als, and Eu
3+
emission om he emaining glassy
phase, sugges ing ha eu opium educ ion occu s in he c ys alline phase. Pho olumines-
cence emission spec a showed a main peak a 484 nm, associa ed wi h ypical T
2g→8
S
7/2
ansi ions o Eu
2+
unde exci a ion a 390 nm in he glass-ce amics. The p esence o Dy
3+
inc eased pe sis ence in he samples mel ed in he gas u nace. Dy
3+
ions a e gene ally
a ibu ed o he o ma ion o deepe aps and inc eased pe sis en luminescence. The e-
sul s o ou la es published esea ch [
27
], acco ding o which only glass-ce amics co-doped
wi h Dy3+ showed some pe sis ence, a e in ag eemen wi h his hypo hesis.
Analysis o he Eu L
3
-edge XANES spec a o he mos pe sis en sample e ealed
ha he Eu
2+
a io was ~4% and ha Eu
2+
was inco po a ed in he c ys alline phase a
a concen a ion o ~0.16 w %. A highe amoun o Eu
2+
was de ec ed in he co-doped
samples ea ed in a educing a mosphe e, bu his did no lead o imp o emen in he
pe sis ence.
We sugges ed ha he luminescence mechanism in ol es he p esence o shallow
elec on aps ha a e suddenly emp ied o empe a u es abo e 100 K. The mos pe sis en
luminescence is likely due o an e ec i e concen a ion o Eu
2+
in he dend i ic-shaped
c ys als, which a e o med o his pa icula composi ion, and wi h a sui able le el o S
acancies, e en hough S acancies a e mos likely o med in e e y sample.
The aim o his esea ch was o s udy he changes in he emission o hese S
2
MgSi
2
O
7
:
Eu
2+
, Dy
3+
glass-ce amics ob ained by sin e ing and c ys allisa ion o glass powde s as
a unc ion o he dopan concen a ions. Glasses o he same base composi ion (55SiO
2
-
27S O-18MgO, mol%.) wi h inc easing Eu
2
O
3
and Dy
2
O
3
concen a ion we e mel ed in a
gas u nace, and hei co esponding glass-ce amics we e ob ained a e sui able he mal
ea men . A comple e s udy o he he mal, s uc u al, and op ical p ope ies allows he
selec ion o an op imum dopan le el con en in o de o achie e highe pe sis ence imes.
2. Expe imen al P ocedu e
2.1. Glasses and Glass-Ce amics P epa a ion
Glasses o he same base composi ion 55SiO
2
-27S O-18MgO mol%. doped wi h di e -
en amoun s o Eu
2
O
3
and Eu
2
O
3
/Dy
2
O
3
we e p epa ed by mel -quenching. The employed
aw ma e ials we e SiO
2
sand (Sain -Gobain, 99.6%), S CO
3
(Al a Aesa , 97.5%), MgO (Pan-
Reac, 98%), Eu
2
O
3
(Al a Aesa , >99.9%), and Dy
2
O
3
(Al a Aesa , >99.9%). Ba ches o 100 g
Ma e ials 2022,15, 3068 4 o 15
we e mixed and s i ed in a Tu bula mixe o one hou o achie e homogenisa ion. The
glasses we e mel ed in a gas u nace in ai using an alumina–zi conia–silica (AZS; Al
2
O
3
-
Z O
2
-SiO
2
) c ucible. The empe a u e was main ained a 1300
◦
C o 15 min, ollowed by
an inc ease o 1550
◦
C o 1 h, wi h inal hea ing o 1600
◦
C. As soon as he u nace eached
1600 ◦C (wi hou dwell ime), he glass was pou ed in o wa e o ob ain a glass i .
The i s we e milled in ace one, and he powde s we e sie ed below 20
µ
m. Cylin-
d ical pelle s (Ø = 2.5 cm) we e p epa ed by p essing he powde in o a die (1600 Kp o
3 min) be o e i ing in an elec ic u nace a 1100
◦
C (hea ing and cooling a e 10
◦
C/min)
o 1 min in he ai a mosphe e.
Table 1summa ises he s udied glass-ce amic samples, whose names indica e ha
hey a e glass-ce amic (GC) samples and he dopan con en in mol%. The glasses and
glass-ce amics we e i s obse ed wi h he naked eye unde he ligh o a UV lamp a
365 nm, which se ed as an exci a ion sou ce. All o iginal glass i s showed ed emission
unde he exci a ion sou ce, and mos glass-ce amics showed blue emission unde he
exci a ion sou ce. As widely discussed in a p e ious pape [
26
], he blue luminescence
is associa ed wi h he T
2g→8
S
7/2
ansi ion o Eu
2+
ions in he S
2
MgSi
2
O
7
c ys als. The
able also lis s he pe sis ence ha he ma e ials showed a oom empe a u e and a 0
◦
C
once he exci a ion sou ce was swi ched o . A e he blue emission ceased, he e was
s ill whi e emission emaining o longe imes, in he case o he highe blue pe sis ence
samples—GC-1Eu-0.5Dy and GC-1Eu-1Dy— he whi e emission eached 152 s and 261 s,
espec i ely [27].
Table 1.
Glass-ce amics nomencla u e and pe sis en blue emission in o ma ion. Measu emen s we e
epea ed 3–4 imes wi h an e o o abou 3 s.
Sample Name Emission unde
UV Lamp (365 nm)
Pe sis en Blue
Emission
a RT (Time)
Pe sis en Blue
Emission
a 0 ◦C (Time)
GC-0.5Eu Blue - -
GC-0.25Eu-0.5Dy Blue 22.96 s 102.52 s
GC-1Eu-0.5Dy Blue 75.90 s 268.29 s
GC-1.2Eu-0.5Dy Blue 39.07 s 146.57 s
GC-1.6Eu-0.5Dy Blue 8.39 s 15.57 s
GC-1Eu-1Dy Blue 83.33 s 272.17 s
GC-2Eu-1Dy Red - -
2.2. The mal and S uc u al Cha ac e isa ion
DTA cu es we e eco ded wi h a SETARAM Se sys E olu ion ins umen , using glass
powde o pa icle size < 20
µ
m wi h hea ing a es 2, 5, 10, 20, and 30
◦
C/min up o
1200 ◦C
.
An EM 201 side- iew ho -s age mic oscope (HSM) wi h image analysis and 1750/15
Leica elec ical u nace was used o de e mine he sin e ing and low beha iou o he glass
powde s. De ails o he equipmen ha e been epo ed p e iously [
28
]. Measu emen s
we e conduc ed in ai a a hea ing a e o 10
◦
C/min on powde samples wi h pa icle
sizes < 20
µ
m. The empe a u e was measu ed wi h a P /Rh (6/30) he mocouple placed
unde he alumina suppo and in con ac wi h i . The changes in he a ea o he samples
a e associa ed wi h di e en p ocesses and co espond o poin s o iscosi y ha we e
p e iously de e mined [29].
The densi y o glass-ce amics was measu ed acco ding o he A chimedes me hod
using dis illed wa e .
The glass-ce amic pelle s we e milled and sie ed o a pa icle size lowe han 60
µ
m
and ini ially cha ac e ised by X- ay di ac ion (B uke D8 Ad ance, Massachuse s, USA) in
he ange o 10–70
◦
2
θ
, wi h a s ep size o 0.02
◦
, employing CuK
α1
adia ion (
λ= 1.54056 Å
).
Ma e ials 2022,15, 3068 5 o 15
Scanning elec on mic oscopy (SEM) o he glass-ce amic samples was pe o med
on a Hi achi S-3000N mic oscope, Tokyo, Japan equipped wi h a acuum chambe . The
ins umen is equipped wi h seconda y elec on (SE) and backsca e ing elec on (BSE)
de ec o s, as well as an Ox o d Ins umen s ene gy-dispe si e X- ay spec oscopy (EDX)
analyse , model INCAx-sigh , and allows samples o be inclined a 90◦.
Scanning elec on mic oscopy–ca hodoluminescence (SEM–CL) o he same selec ed
glass-ce amic samples was pe o med on a Hi achi S-3000N mic oscope equipped wi h a
acuum chambe , on exci a ion wi h an elec on beam o ol age 15–25 kV and a ilamen
in ensi y o 100
µ
Å. The emission spec a we e eco ded employing a ibe spec ome e
wi h a cha ge-coupled de ice (CCD) h ough an op ical ibe , and he co esponding
luminescence pho og aphs, wi h an o dina y came a. The ins umen is equipped wi h
seconda y elec on (SE) and backsca e ed elec on (BSE) de ec o s, an ene gy-dispe si e
X- ay spec oscope (EDX) Quan ax (model XFlash 6I30, B uke , Massachuse s, USA), and
a ca hode-luminescence sys em (CHROMA-CL2 Ga an, Pleas on, CA, USA). Samples we e
composi ionally accu a e wi hin he unce ain y in he EDX (~1%). Addi ionally, spec ally
esol ed CL measu emen s we e ca ied ou a 80 K on a MONO-CL2 sys em (Ga an,
Pleas on, CA, USA) a ached o a ield-emission scanning elec on mic oscope (FE-SEM,
ZeissLEO 1530, Jena, Ge many). De ec ion was pe o med wi h a pho omul iplie o
panch oma ic images, and a Pel ie cooled Si-CCD o spec ally esol ed images.
2.3. Op ical Cha ac e isa ion
The glass-ce amic pelle s we e i s ly obse ed unde UV ligh (18 W (
λ
= 365 nm),
I = 0.025 mA/cm2) o check o emission and pe sis ence o phospho escence.
Room empe a u e emission and exci a ion spec a, as well as empo al decays, we e
measu ed in an Edinbu gh FS5 Spec o luo ome e equipped wi h a 150 W Xenon lamp.
The emission was de ec ed by he Hamama su R928P pho omul iplie . The pe sis en
luminescence decays we e ob ained a e illumina ion o he samples in he UV (354 nm)
wi h he Xe lamp o 10 min. A e ha , he illumina ion was blocked and he luminescence
decays we e moni o ed o 600 s wi h a esolu ion o 0.5 s.
3. Resul s and Discussion
3.1. The mal and S uc u al P ope ies
The e ec o di e en hea ing a es on he c ys allisa ion empe a u es ob ained om
DTA cu es is illus a ed in Figu e 1and Table 2 o he G-undoped glass. On inc easing
he hea ing a e, he nuclea ion ime dec eased and, as a esul , he c ys allisa ion peaks
appea ed a a highe empe a u e.
Ma e ials2022,15,xFORPEERREVIEW6o 16



Figu e1.DTAcu eso  heundopedglasswi hdi e en hea ing a es(ø<20μm).
Table2.T
g
,T
x
,andT
c
o  heundopedglass(ø<20μm)de e minedbyDTA.
Hea ingRa eT
g
(°C)±7T
x
(°C)±9T
c1
(°C)±9T
c2
(°C)±9
2°C/min‐8789861082
5°C/min7208919911085
10°C/min72090110061106
20°C/min72290910291129
30°C/min71792810271141
Figu e2aandTable3 ep esen  heDTA esul s o composi ionsdopedwi hdi e ‐
en Eu/Dyconcen a ionsandapa iclesize<20μm.Theaddi iono dopan  esul edin
ahighe glass ansi ion empe a u e(T
g
).Va ia ionsin hec ys allisa iono  hesamples
we eobse edwhenchanging henumbe o dopan s.In heco‐dopedsamples(wi h
0.5%Dy),c ys allisa ionwasobse ed oslowdownwi hinc easingeu opiumconcen a‐
ion.In heco‐dopedsamples(wi h1%Dy), hesameoccu ed—i.e.,c ys allisa ionwas
slowe as henumbe o eu opiuminc eased.Figu e2bshows heHSM esul s o glass
powde swi hdi e en dopan concen a ions;sin e ingand low empe a u esa egi en
inTable4.Theso ening empe a u e(T
S
)wasbe ween780and840°C o allsamples.In
gene al, hesamplesbecamesphe icala ound1000–1100°C,bu sampleG‐1Eu‐0.5Dydid
no becomesphe icalun il1140°C.Allsamples eachedhal ‐ball empe a u e(T
HB
)abo e
1150°Cand hen lowed.
Figu e 1. DTA cu es o he undoped glass wi h di e en hea ing a es (ø < 20 µm).

Ma e ials 2022,15, 3068 6 o 15
Table 2. Tg, Tx, and Tco he undoped glass (ø < 20 µm) de e mined by DTA.
Hea ing Ra e Tg(◦C) ±7 Tx(◦C) ±9 Tc1(◦C) ±9 Tc2(◦C) ±9
2◦C/min - 878 986 1082
5◦C/min 720 891 991 1085
10 ◦C/min 720 901 1006 1106
20 ◦C/min 722 909 1029 1129
30 ◦C/min 717 928 1027 1141
Figu e 2a and Table 3 ep esen he DTA esul s o composi ions doped wi h di e en
Eu/Dy concen a ions and a pa icle size < 20
µ
m. The addi ion o dopan esul ed in a
highe glass ansi ion empe a u e (T
g
). Va ia ions in he c ys allisa ion o he samples we e
obse ed when changing he numbe o dopan s. In he co-doped samples (wi h 0.5%Dy),
c ys allisa ion was obse ed o slow down wi h inc easing eu opium concen a ion. In he
co-doped samples (wi h 1%Dy), he same occu ed—i.e., c ys allisa ion was slowe as he
numbe o eu opium inc eased. Figu e 2b shows he HSM esul s o glass powde s wi h
di e en dopan concen a ions; sin e ing and low empe a u es a e gi en in Table 4. The
so ening empe a u e (T
S
) was be ween 780 and 840
◦
C o all samples. In gene al, he
samples became sphe ical a ound 1000–1100
◦
C, bu sample G-1Eu-0.5Dy did no become
sphe ical un il 1140
◦
C. All samples eached hal -ball empe a u e (T
HB
) abo e 1150
◦
C and
hen lowed.
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Figu e2.(a)DTAand(b)HSMcu eso G‐undoped,G‐0.25Eu‐0.5Dy,G‐1Eu‐0.5Dy,G‐1.2Eu‐0.5Dy,
andG‐1.6Eu‐0.5Dyglasseswi hdi e en dopan concen a ions.Hea ing a e:10°C/min.
Table3.T
g
,T
x
,andT
c
o allglass(ø<20μm)samplesde e minedwi hDTA.
SampleT
g
(°C)±7T
x
(°C)±9T
c
(°C)±9
G‐undoped7209011006
G‐0.5Eu721887967
G‐0.25Eu‐0.5Dy727895959
G‐1Eu‐0.5Dy728897960
G‐1.2Eu‐0.5Dy746911989
G‐1.6Eu‐0.5Dy7379221000
G‐1Eu‐1Dy743897961
G‐2Eu‐1Dy7489171000
Table4.Sin e ingand low empe a u eso glass(ø<20μm)samplesde e minedwi hHSM.
SampleT
FS
(°C)
±10
T
MS
(°C)
±10
T
S
(°C)
±10
Sphe e(°C)
±10
T
HB
(°C)
±3
T
F
(°C)
±3
G‐undoped790910940100011591190
G‐0.5Eu780890920102011901197
G‐0.25Eu‐0.5Dy78010101030109011701190
G‐1Eu‐0.5Dy8208801020110011741200
G‐1.2Eu‐0.5Dy810890990110011601176
G‐1.6Eu‐0.5Dy8409201030109011481159
G‐1Eu‐1Dy8309501100114011601180
G‐2Eu‐1Dy840910948100011841195
Thecombina iono DTAandHSM esul sindica ed ha hea  ea men o  heglass
powde sup o1100°Ccanp o idesui ablesin e ing,c ys allisa ion,and lows ages, hus
allowing hep oduc iono glass‐ce amicinbulko enamel o maspossible inalp od‐
uc s.
Thedensi ieso  heglass‐ce amicswe emeasu edby heA chimedesme hod,bu 
o  hedensi yo  heglasssamples,weadop ed he alueo  hemel sinanelec ic u ‐
naceasa e e ence,since,asp e iouslymen ioned o  hegas u nace, heglassmel edin
aglass i  o m.Thea e agedensi yo  heglassmel edin heelec ic u nacewasabou 
3.31g∙cm
−3
,and hedensi yo glass‐ce amicsisp esen edinTable5.The heo e icalden‐
si yo  hemainc ys allinephase,S
2
MgSi
2
O
7
,was3.7g∙cm
−3
,while hehighes densi y
ob ained o  heglass‐ce amicswas3.27g∙cm
−3
o GC‐1Eu‐0.5Dy.Al houghi wasno 
quan i ied, he ewasahigh esidualpo osi yinsomeo  hesamples.
Figu e 2.
(
a
) DTA and (
b
) HSM cu es o G-undoped, G-0.25Eu-0.5Dy, G-1Eu-0.5Dy, G-1.2Eu-0.5Dy,
and G-1.6Eu-0.5Dy glasses wi h di e en dopan concen a ions. Hea ing a e: 10 ◦C/min.
Table 3. Tg, Tx, and Tco all glass (ø < 20 µm) samples de e mined wi h DTA.
Sample Tg(◦C) ±7 Tx(◦C) ±9 Tc(◦C) ±9
G-undoped 720 901 1006
G-0.5Eu 721 887 967
G-0.25Eu-0.5Dy 727 895 959
G-1Eu-0.5Dy 728 897 960
G-1.2Eu-0.5Dy 746 911 989
G-1.6Eu-0.5Dy 737 922 1000
G-1Eu-1Dy 743 897 961
G-2Eu-1Dy 748 917 1000
Ma e ials 2022,15, 3068 7 o 15
Table 4. Sin e ing and low empe a u es o glass (ø <20 µm) samples de e mined wi h HSM.
Sample TFS(◦C)
±10
TMS(◦C)
±10
TS(◦C)
±10
Sphe e(◦C)
±10
THB(◦C)
±3
TF(◦C)
±3
G-undoped 790 910 940 1000 1159 1190
G-0.5Eu 780 890 920 1020 1190 1197
G-0.25Eu-0.5Dy 780 1010 1030 1090 1170 1190
G-1Eu-0.5Dy 820 880 1020 1100 1174 1200
G-1.2Eu-0.5Dy 810 890 990 1100 1160 1176
G-1.6Eu-0.5Dy 840 920 1030 1090 1148 1159
G-1Eu-1Dy 830 950 1100 1140 1160 1180
G-2Eu-1Dy 840 910 948 1000 1184 1195
The combina ion o DTA and HSM esul s indica ed ha hea ea men o he glass
powde s up o 1100
◦
C can p o ide sui able sin e ing, c ys allisa ion, and low s ages, hus
allowing he p oduc ion o glass-ce amic in bulk o enamel o m as possible inal p oduc s.
The densi ies o he glass-ce amics we e measu ed by he A chimedes me hod, bu o
he densi y o he glass samples, we adop ed he alue o he mel s in an elec ic u nace as a
e e ence, since, as p e iously men ioned o he gas u nace, he glass mel ed in a glass i
o m. The a e age densi y o he glass mel ed in he elec ic u nace was abou 3.31 g
·
cm
−3
,
and he densi y o glass-ce amics is p esen ed in Table 5. The heo e ical densi y o he
main c ys alline phase, S
2
MgSi
2
O
7
, was 3.7 g
·
cm
−3
, while he highes densi y ob ained
o he glass-ce amics was 3.27 g
·
cm
−3
o GC-1Eu-0.5Dy. Al hough i was no quan i ied,
he e was a high esidual po osi y in some o he samples.
Table 5. Glass-ce amic densi ies.
Sample Glass-Ce amic Densi y ±0.01 (g/cm3)
GC-undoped 3.11
GC-0.5Eu 3.17
GC-0.25Eu-0.5Dy 3.19
GC-1Eu-0.5Dy 3.27
GC-1.2Eu-0.5Dy 3.26
GC-1.6Eu-0.5Dy 3.19
GC-1Eu-1Dy 3.22
GC-2Eu-1Dy 3.21
3.2. X- ay Di ac ion
Figu e 3shows he X- ay di ac ion pa e ns o some o he glass-ce amics ea ed
a 1100
◦
C o 1 min. As can be seen in sample GC-undoped and GC-1Eu-0.5Dy, only
he S
2
MgSi
2
O
7
phase (ICDD: 75–1736) appea ed. The inc ease in he numbe o dopan s,
bo h eu opium and dysp osium, esul ed in he appea ance o wo small peaks, no co -
esponding o he ake mani e phase. These uniden i ied peaks a e shown in samples
GC-1.6Eu-0.5Dy, GC-1Eu-1Dy, and GC-2Eu-1Dy in Figu e 3.
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Table5.Glass‐ce amicdensi ies.
SampleGlass‐Ce amicDensi y±0.01(g/cm
3
)
GC‐undoped3.11
GC‐0.5Eu3.17
GC‐0.25Eu‐0.5Dy3.19
GC‐1Eu‐0.5Dy3.27
GC‐1.2Eu‐0.5Dy3.26
GC‐1.6Eu‐0.5Dy3.19
GC‐1Eu‐1Dy3.22
GC‐2Eu‐1Dy3.21
3.2.X‐RayDi ac ion
Figu e3shows heX‐ aydi ac ionpa e nso someo  heglass‐ce amics ea eda 
1100°C o 1min.AscanbeseeninsampleGC‐undopedandGC‐1Eu‐0.5Dy,only he
S
2
MgSi
2
O
7
phase(ICDD:75–1736)appea ed.Theinc easein henumbe o dopan s,bo h
eu opiumanddysp osium, esul edin heappea anceo  wosmallpeaks,no co e‐
sponding o heake mani ephase.Theseuniden i iedpeaksa eshowninsamplesGC‐
1.6Eu‐0.5Dy,GC‐1Eu‐1Dy,andGC‐2Eu‐1DyinFigu e3.


Figu e3.XRDpa e nso glass‐ce amicsamples ea eda 1100°C o 1min.
3.3.SEMandCL–SEM
AnSEManalysiso  hepolishedsu aceo glass‐ce amicsampleswasca iedou .
Noinc easein hesizeo  hec ys alswasobse ed,whichinmos glass‐ce amicsamples,
we e oundedc ys als(2μm)in heS
2
MgSi
2
O
7
phase.InGC‐1Eu‐0.5Dy, hec ys alsap‐
pea edwi hadi e en shape: heyg ewinadend i ic o m,and hei sizewasla ge (4–
6μm).Figu e4showsSEMimageso GC‐undoped,GC‐1Eu‐0.5Dy,GC‐1Eu‐1Dy,and
GC‐2Eu‐1Dy.I ispossible oapp ecia e he e ydi e en mic os uc u es.In heGC‐
undoped(Figu e4a),onlyone ypeo c ys al(poin 1)co esponding o heake mani e
phasewasobse ed,and hec ys alswe esmalland ounded.Poin s2and3co espond
o he esidualglassyphase.ThesampleGC‐1Eu‐0.5Dy(Figu e4b)showeddend i ic o m
c ys als(mo e han10μm) ha alsoco esponded o heake mani ephase(poin 1).In
compa ison,inGC‐1Eu‐1Dy(Figu e4c)andGC‐2Eu‐1Dy(Figu e4d), he ewe e wo
ypeso c ys als; hec ys alsco esponding o heake mani ephasewe eagainsmall(2
Figu e 3. XRD pa e ns o glass-ce amic samples ea ed a 1100 ◦C o 1 min.
3.3. SEM and CL–SEM
An SEM analysis o he polished su ace o glass-ce amic samples was ca ied ou .
No inc ease in he size o he c ys als was obse ed, which in mos glass-ce amic samples,
we e ounded c ys als (2
µ
m) in he S
2
MgSi
2
O
7
phase. In GC-1Eu-0.5Dy, he c ys als
appea ed wi h a di e en shape: hey g ew in a dend i ic o m, and hei size was la ge
(4–6
µ
m). Figu e 4shows SEM images o GC-undoped, GC-1Eu-0.5Dy, GC-1Eu-1Dy, and
GC-2Eu-1Dy. I is possible o app ecia e he e y di e en mic os uc u es. In he GC-
undoped (Figu e 4a), only one ype o c ys al (poin 1) co esponding o he ake mani e
phase was obse ed, and he c ys als we e small and ounded. Poin s 2 and 3 co espond
o he esidual glassy phase. The sample GC-1Eu-0.5Dy (Figu e 4b) showed dend i ic
o m c ys als (mo e han 10
µ
m) ha also co esponded o he ake mani e phase (poin 1).
In compa ison, in GC-1Eu-1Dy (Figu e 4c) and GC-2Eu-1Dy (Figu e 4d), he e we e wo
ypes o c ys als; he c ys als co esponding o he ake mani e phase we e again small
(2
µ
m) and ounded (poin 2 in bo h cases). In addi ion, hese glass-ce amics p esen ed
elonga ed whi e c ys als (poin 1 in bo h cases), co esponding o he uniden i ied phase,
he chemical analysis o which is shown in Table 6; his phase was ich in SiO
2
and S O.
Poin 3 co esponds o he esidual glassy phase. In he sample GC-2Eu-1Dy, hese whi e
c ys als p edomina ed, al hough some small c ys als o he S
2
MgSi
2
O
7
phase could also
be obse ed. These esul s coincide wi h hose ob ained p e iously by X- ay di ac ion.
EDX analysis o he o iginal glass i s was ca ied ou o de e mine i he e was
alumina o zi conia inco po a ion om he AZS c ucible (Table 7). All glass composi ions
con ained some alumina pe cen age. The EDX analysis o he p e iously men ioned poin s
in Figu e 4in he glass-ce amic samples is shown in Table 7.
Figu e 5shows an elemen al map o GC-1Eu-1Dy in which i can be seen again how
eu opium and dysp osium a e concen a ed in he whi e c ys als, coinciding wi h he
EDX analysis o he same sample. In he g ay c ys als, he elemen s co esponding o he
ake mani e phase, s on ium, silicon, and magnesium we e clea ly ound.
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

μm)and ounded(poin 2inbo hcases).Inaddi ion, heseglass‐ce amicsp esen edelon‐
ga edwhi ec ys als(poin 1inbo hcases),co esponding o heuniden i iedphase, he
chemicalanalysiso whichisshowninTable6; hisphasewas ichinSiO
2
andS O.Poin 
3co esponds o he esidualglassyphase.In hesampleGC‐2Eu‐1Dy, hesewhi ec ys‐
alsp edomina ed,al houghsomesmallc ys also  heS
2
MgSi
2
O
7
phasecouldalsobe
obse ed.These esul scoincidewi h hoseob ainedp e iouslybyX‐ aydi ac ion.

Figu e4.SEMimageso (a)GC‐undoped,(b)GC‐1Eu‐0.5Dy,(c)GC‐1Eu‐1Dy,and(d)GC‐2Eu‐1Dy
glass‐ce amics.
Table6.Composi ionalanalysis(mol%.)o GC‐Undoped,GC‐1Eu‐0.5Dy,GC‐1Eu‐1Dy,andGC‐
2Eu‐1Dyglass‐ce amicsasde e minedbyEDXco esponding o hepoin sshowninFigu e4.
SiO
2
S OMgOAl
2
O
3
Eu
2
O
3
Dy
2
O
3

GC‐Undoped
Theo e icalglasscomposi ion55.027.018.0‐ ‐ ‐
1S
2
MgSi
2
O
7
40.939.517.32.4‐ ‐
262.121.111.75.1‐ ‐
360.121.416.81.0‐ ‐
GC‐1Eu‐0.5Dy
Theo e icalglasscomposi ion54.126.617.700.90.5
1S
2
MgSi
2
O
7
40.938.117.92.00.50.2
256.620.416.24.01.70.8
GC‐1Eu‐1Dy
Theo e icalglasscomposi ion53.926.417.600.90.9
150.834.96.81.92.72.7
2S
2
MgSi
2
O
7
41.139.518.00.80.30.0
362.123.210.42.30.81.0
GC‐2Eu‐1Dy
Theo e icalglasscomposi ion53.426.217.401.90.9
164.026.11.72.14.31.6
2S
2
MgSi
2
O
7
39.738.420.01.30.40.0
Figu e 4.
SEM images o (
a
) GC-undoped, (
b
) GC-1Eu-0.5Dy, (
c
) GC-1Eu-1Dy, and (
d
) GC-2Eu-1Dy
glass-ce amics.
Table 6.
Composi ional analysis (mol%.) o GC-Undoped, GC-1Eu-0.5Dy, GC-1Eu-1Dy, and GC-2Eu-
1Dy glass-ce amics as de e mined by EDX co esponding o he poin s shown in Figu e 4.
SiO2S O MgO Al2O3Eu2O3Dy2O3
GC-Undoped
Theo e ical glass composi ion 55.0 27.0 18.0 - - -
1 S 2MgSi2O740.9 39.5 17.3 2.4 - -
2 62.1 21.1 11.7 5.1 - -
3 60.1 21.4 16.8 1.0 - -
GC-1Eu-0.5Dy
Theo e ical glass composi ion 54.1 26.6 17.7 0 0.9 0.5
1 S 2MgSi2O740.9 38.1 17.9 2.0 0.5 0.2
2 56.6 20.4 16.2 4.0 1.7 0.8
GC-1Eu-1Dy
Theo e ical glass composi ion 53.9 26.4 17.6 0 0.9 0.9
1 50.8 34.9 6.8 1.9 2.7 2.7
2 S 2MgSi2O741.1 39.5 18.0 0.8 0.3 0.0
3 62.1 23.2 10.4 2.3 0.8 1.0
GC-2Eu-1Dy
Theo e ical glass composi ion 53.4 26.2 17.4 0 1.9 0.9
1 64.0 26.1 1.7 2.1 4.3 1.6
2 S 2MgSi2O739.7 38.4 20.0 1.3 0.4 0.0
3 63.8 15.7 14.2 3.4 1.7 0.9