2017ФотолюмКерамПлатовИнгл

DOI 10.1007/s10717-017-9900-9
Glass and Ceramics, Vol. 73, Nos. 11 – 12, March, 2017 (Russian Original, Nos. 11 – 12, November – December, 2016)
UDC 666.5:535.37
PHOTOLUMINESCENCE CENTERS IN PORCELAIN
V. A. Rassulov,1 R. A. Platova,2, 3 and Yu. T. Platov2
Translated from Steklo i Keramika, No. 11, pp. 22 – 26, November, 2016.
Time-resolved luminescence with excitation by molecular-nitrogen laser radiation was used to study samples
of porcelain. A combination of bands of optically active centers [OAC] was found in the photoluminescence
spectra of hard, soft, and bone porcelain: proper centers Î*Si and Î*Al and impurity centers Mn2+, Cr3+, Fe3+,
Dy3+, and Sm3+ as well as molecular centers [UO2 ]2+. A band of the OAC Fe3+, differing in intensity, was identified in all three porcelain samples.
Key words: porcelain, photoluminescence, luminescence spectrum, luminogens, optically active centers.
fectively without knowing the basic physical processes responsible for the radiation and without an extensive database
on spectral-kinetic properties of the radiation emission from
porcelain with different chemical and phase composition.
The aim of the present work is to identify the optically
active centers of photoluminescence in porcelains differing
in composition and to validate the physical and chemical
models of the centers emitting in the optical range of the
electromagnetic spectrum.
Luminescence spectroscopy is an effective method for
studying trace elements and defects of silicate minerals,
glass, and ceramics [1]. Considerable progress in our understanding of the nature of luminescence has been achieved
with the advent of pulse technology [2]. The efficacy of laser
radiation in such studies has been shown [3, 4]. Time-resolved luminescence and laser sources (time-resolved laser-induced) can be used, in addition to EPR (Electron Paramagnetic Resonance), EXAFS (Extended x-ray Fine Structure Absorption), and XANES (x-ray Absorption Near-edge
Spectroscopy), to obtain information about the coordination-valence state of optically active centers (OAC) of
photoluminescence.
As far as we know the luminescence of porcelain has not
been studied [5]. Porcelain should be regarded as a complex
heterogeneous system consisting of silicate minerals inside a
glassy phase. Extensive material has been accumulated on
the luminescence properties of the minerals [3, 4, 6] present
in the raw materials used for ceramic pastes (quartz, feldspar,
kaolinite, and others) and glasses [7]. Depending on the composition of the porcelain (hard or soft feldspar and bone) this
system includes a great diversity of isomorphic and impurity
elements, cationic and anionic vacancies, different impurity-vacancy groups forming a large number of electron and
hole centers, many of which are optically active.
On the whole, however, the same impurity-luminogens
and types of defects in here in porcelain as in other silicate
materials [1, 6]. Luminescence analysis cannot be used ef-
OBJECTS AND METHODS OF INVESTIGATION
A study of the luminescence of 109 specimens of porcelain articles differing in composition (solid, bone, and soft)
and country of origin (England, Belarus, Germany, China,
Latvia, Russia, Romania, Ukraine, Czech Republic, and Japan) revealed the OAC characteristic for them.
The luminescence spectra of porcelain (Table 1) with the
most distinct optically active centers characterizing all experimental samples are displayed in Fig. 1a – d.
The investigations of the photoluminescence were conducted on a computerized complex using a microspectrophotometer (MSFU-312, NPO LO-MO, Russia), a N2-laser
with radiation wavelength 337.1 nm (3.67 eV) (LGI-505,
NPO Plasma, Russia), and a detection system in the
CAMAC standard (ÉZAN, Russia) [8]. The spectral and kinetic measurements were performed using copyrighted software working in the Windows XP environment.
The use of a molecular nitrogen laser is justified by:
short duration (10 nsec), high power, narrow emission band
in the mid-UV range, absence of spurious radiation in the
1
N. M. Fedorovskii All-Russia Institute of Mineral Raw Materials,
Moscow, Russia(e-mail: rassulov@mail.ru).
2
G. V. Plekhanov Russian Economics University, Moscow, Russia.
3
E-mail: raisa.platova@yandex.ru.
410
0361-7610/17/1112-0410 © 2017 Springer Science+Business Media New York
Photoluminescence Centers in Porcelain
411
Intensity, arb. units, ´1000
7
a
6
5
Sample
no.
4
1
3
2
2
3
4
1
Intensity, arb. units, ´1000
0
7
Intensity, arb. units, ´1000
Country
of origin
Branding
Russia
Imperial porcelain St. Peterburg,
bone china
China
Fine Porcelian Collection
Rumania Porcelain manufacturers Moga
Russia
Imperial porcelain St. Peterburg
Porcelain
type
Bone
Soft
Hard
Hard
b
6
5
4
3
2
1
0
2.0
c
1.5
1.0
0.5
0
Intensity, arb. units, ´1000
TABLE 1. List of Porcelain Samples with Typical Luminescence
Centers
5
d
4
3
2
which makes it possible to estimate the decay kinetics of the
identified centers. The time-integrated spectrum in the range
of 390 – 850 nm with a 2 nm step and spectral resolution
2 nm was recorded first, after which the spectrum was recorded without changing the position of the sample and with
time delay 180 msec after the laser pulse, which are marked
by Z in the spectra. With time delay 180 msec after the laser
pulse only bands with a long decay time are recorded, so that
their intensity can be determined more accurately and weak
lines of the rare earths Dy3+ and Sm3+, which, as a rule, have
a considerable decay time, can be observed.
The wavelength calibration of the spectrometer was performed using a DRGS-12 helium-mercury lamp. The spectral sensitivity of the setup was taken into account in terms of
the radiation of the TRSh2850-3000 spectrometric incandescent lamp, using Planck’s formula to account for the wavelength dependence of the radiance. The sensitivity of the
setup and the power of the laser radiation were monitored at
the peak of the luminescence band (lmax ~ 530 nm) of
ZhS-19 uranium glass included in the microspectrophotometer set.
1
RESULTS AND DISCUSSION
0
Wavelength, nm
Fig. 1. Luminescence spectra of porcelain: spectrum with 180 msec
delay of detection after the laser pulse Z; a, b, c, d ) sample
Nos. 1 – 4 in Table 1.
visible and near-infrared ranges, and low maintenance cost,
and high reliability.
The measurements were performed at room temperature
at several points in unglazed locations of porcelain samples
in 0–0 geometry. The diameter of the photometric section
was 0.05 mm. The decay times of most impurity OAC are
significantly longer than the emission times of the quartz-fluorite lens in the high-power laser radiation in the microscope.
The detection system makes it possible to measure the
luminescence spectrum without delay after the laser pulse
(time integral spectrum) as well as the luminescence spectrum with a delay equal to 180 mm after the laser pulse,
The type of optically active centers in porcelain was
identified according to the position of the peak and the
half-width of the band (Table 2) and the decay kinetics determined from the time integrated spectrum and with delayed
detection after the laser pulse (Table 2, Fig. 2) assuming a
single decay exponential characteristic for many impurity
centers. An analysis of the obtained luminescence spectra
identified the following OAC in porcelain.
OXYGEN CENTER (O* )
The blue-violet luminescence band associated with intrinsic defects is characteristic for many oxygen-containing
minerals and glasses [4, 6, 7]. The luminescence of quartz,
feldspars, and natural and synthetic glass is associated with
4the centers SiO34 and AlO 4 [6, 7]. These centers are to one
degree or another manifested in all porcelain samples
(Fig. 1a – d ), but in bone china (Fig. 1a ) it is very weak. In
412
V. A. Rassulov et al.
TABLE 2. Optical and Spectroscopic Characteristics of Optically
Active Centers of Photoluminescence in Porcelain
OAC
O* (Si)
O* (Al)
[UO2 ]2+
Mn2+
Cr3+
Fe3+
Dy3+
Sm3+
lmax , nm
FWHM, eV
t, msec
416 – 420
447 – 455
525 – 532
560 – 568
688 – 692
0.33 – 0.35
0.45 – 0.57
0.25 – 0.50
0.50 – 0.60
^1
^1
180
440
240
716 – 738
489; 576
640
~0.1
0.15 – 0.33
–
–
620
–
–
Notations: lmax ) range of the maximum of the position of the center of the band; FWHM (half-height line width) OAC] width of the
band at half height; t) e-fold attenuation time of the band intensity.
soft porcelain (Fig. 1b ) the O*Al-center (lmax ~ 447 – 455 nm)
is clearly manifested, but in hard porcelain (Fig. 1c ) O*Si
(lmax ~ 416 – 420 nm) is observed. When the luminescence
band of the OAC Cr3+ appears in the spectrum (Fig. 1d ) the
intensity of this center falls sharply. According to [4] these
centers are designated as O*, indicating that the element responsible for this band is an oxygen containing center whose
excited state prior to radiation emission is designated by an
asterisk.
Studies of native quartz, modified by solid-phase diffusion activation of Li, Na, and OH, with excitation by x-rays
or intense ultraviolet radiation from a molecular-nitrogen laser identified an ‘oxygen center’ band in the luminescence
*
spectrum [9]. The center SiO34 (O Si ) with a maximum of
the luminescence band (lmax ~ 400 nm) is unstable at room
temperature and its stability requires appropriate local charge
compensation [6]. The maximum of the AlO4(O*Al )
4
(lmax ~ 460 – 470 nm) emission band in the luminescence of
oxygen-containing minerals lies in the blue region of the
spectrum [6]. Predominance of the center O*Si and/or O*Al
leads to a shift of the resulting band maximum in the luminescence spectrum of porcelain to one (O*Si lmax ~ 416 –
420 nm) or the other (O*Al lmax ~ 450 nm) optically active
center.
OAC [UO2 ]2+. The strong structured band in the green
region (lmax ~ 530 – 532 nm) of the luminescence spectrum
of uranyl is characteristic for all samples of bone china (see
Fig. 1a ). In hard porcelain this band (lmax ~ 525 – 532 nm)
can be strong and is very rarely weak — in samples of soft
porcelain.
The cation U6+ creates an OAC mainly in the form of the
uranyl molecular center [UO2 ]2+ [6, 10], possessing high individuality as a result of characteristic features of the local
environment and the specifics of the electronic structure–band structuredness and long luminescence decay time.
Intensity Z, arb. units, ´1000
14
12
y = 0.779x – 0.212
R 2 = 0.977
10
8
6
4
2
0
5
y = 0.369x – 0.859
R 2 = 0.974
10
15
Intensity, arb. units, ´1000
20
Fig. 2. Arrangement of the points corresponding to porcelain samples in the coordinates luminescence intensities of the bands of the
OAC Fe3+ (p) and [UO2 ]2 (:), measured without detection delay
(along the abscissa) and with detection delay by 180 msec after the
laser pulse (along the ordinate).
The centers of the luminescence bands of the OAC
[UO2 ]2+ with a characteristic frequency are indicated in
Fig. 1a by arrows.
For the same content of uranyl the luminescence intensity is higher in phosphate glasses, whose anions consist of
chains of tetrahedra PO34 where there are no obstacles to the
formation of the nearest environment of uranyl located between the chains, in contrast to the silicate glasses with a
rigid silicon-oxygen frame [11].
OAC Mn2+. The OAC Mn2+ luminescence band in the
yellow region of the spectrum (lmax ~ 560 – 568 nm) is seen
only in soft porcelain samples (see Fig. 1b ). Mn2+ is one of
the most prevalent and well-studied activators of luminescence in minerals and glasses [1, 12]. Since electronic transitions are forbidden in Mn2+ in highly symmetric fields the afterglow duration increases, which also makes it possible to
detect its luminescence in spectra with detection delays after
the laser pulse.
OAC Cr3+. The narrow band with varying intensity
characterizing the R-line, not resolved by the instruments, of
OAC Cr3+ luminescence in the red region of the spectrum
(lmax ~ 688 – 692 nm) has been observed in only some hard
and soft porcelain samples.
The Cr3+ ions located in octahedral coordination create
in the visible region of the spectrum two wide absorption
bands whose peaks are shifted depending on the forces converging on an ion. In these bands strong luminescence is excited with a line spectrum (R-lines) in the red region of the
spectrum (lmax = 690 nm). The presence of wide bands and
very narrow bands in the excitation and luminescence spectra is explained by two systems of Cr3+ terms in the crystal
lattice. The narrow bands in the absorption and luminescence
spectra are created by intercombination transitions between
levels whose splitting does not change with a change in the
magnitude of the crystal field [1]. The narrowness of these
bands and the possibility of precise determination of their
Photoluminescence Centers in Porcelain
spectral position make it possible to reliably identify the ion
Cr3+.
OAC Fe3+. The OAC Fe3+ luminescence band with different intensity in the red region of the spectrum (lmax ~
716 – 738 nm) has been identified in all porcelain samples
(see Fig. 1a – d ). The expansion of the spectral range of the
investigations performed in the near-infrared region
(650 – 850 nm) made it possible to determine the luminescence bands of Fe3+ in many aluminum silicates, including
porcelain and metakaolin [5], predicted long ago by Orgel
[12]. Thus, under x-ray excitation all the experimental samples of feldspars exhibit luminescence in the red region of
the spectrum (710 – 780 nm); the peak of the band shifts depending on the composition. A combined study by means of
luminescence and ESR showed [6] that the centers of luminescence are tetrahedrally coordinated Fe3+ ions occupying
Al and Si positions. The radiation Fe3+ centers with somewhat different parameters causes inhomogeneous broadening
of the band. Fe3+ luminescence is characterized by a Gaussian and decay times of a few milliseconds.
OAC Dy3+ and Sm3+.The luminescence bands characteristic for the trivalent rare earths Dy3+ (see Fig. 1b ) and
Sm3+ were found in the spectra of several porcelain samples
[6].
OAC Fe3+ and [UO2 ]2+ Decay Kinetics. To analyze the
decay kinetics and calculate the intensities of OAC band intensities using the Origin 8.1 software the wavelength measured in nanometers was converted into energy units — electron-volts (eV). A deconvolution process was performed using Gaussian functions and the minimum number of components. The results were characterized by the regression coefficient (R 2 > 0.94).
The location of the points corresponding to porcelain
samples in the coordinates of the luminescence intensities
OAC Fe3+ and OAC [UO2 ]2+ bands measured without delays
and with detection delays by 180 msec after the laser pulse is
shown in Fig. 2. The high linearity of the intensity ratios of
the OAC Fe3+ and OAC [UO2 ]2+ luminescence bands for
different porcelain samples, measured without delays and
with a delay by 180 msec after the laser pulse, attests the constancy of the decay kinetics and independence from band intensity.
OAC Quenching by Impurity Transition Elements.
For a long time it was thought that iron ions only act as luminescence quenchers [6]. As the iron content increases, concentration quenching of the OAC Fe3+ luminescence bands
occurs as a result of the formation of exchange-coupled pairs
Fe–O–Fe, which decrease the concentration of the centers
participating in the radiation.
The presence of transition-element impurities leads to
quenching of the luminescence of both oxygen centers O*Si
and O*Al in the 400 and 460 nm bands lying in the absorption
range of Mn2+, Cr3+, and Fe3+ ions, owing to inductive resonance and exchange interaction, taking account of the fact
that hole centers usually form in tetrahedra adjoining the im-
413
purity centers. As the concentration of Fe3+ centers increases,
the intensity of their radiation passes through a maximum
and decreases because of external quenching, which is attributed to competition for trapping free charge carriers in recombination processes between centers of, on the one hand,
3tetrahedrally coordinated FeO44 and, on the other, SiO 4 and
AlO44 and with the transfer of excitation energy from the
last Fe3+ centers by inductive resonance, since the emission
bands of O*Si and O*Al centers completely overlap with the
absorption bands of Fe3+ ions.
CONCLUSIONS
A combination of OAC bands was found in the photoluminescence spectra of solid samples of soft and bone porcelain with excitation by radiation pulses from a molecular-nitrogen laser: proper O*Si, O*Al and impurity centers
Mn2+, Cr3+, Fe3+ as well as molecular [UO2 ]2+. The
photoluminescence OAC in porcelain was identified on the
basis of optical and spectroscopic parameters — the position
of the center, the half-width, and the decay kinetics.
Both centers are observed in the photoluminescence
spectrum: O*Al (lmax ~ 460 – 470 nm) and O*Si (lmax ~
400 nm). The peak (lmax ~ 450 nm) of the resulting band of
the O* center of luminescence of porcelain shifts when the
concentration of the center O*Al predominates.
A strong structured OAC [UO2 ]2+ luminescence band in
the green region of the spectrum (lmax ~ 530 nm) was identified in all samples of bone china and a weak band or usually
no band in hard and soft porcelain samples (lmax ~ 525 –
532 nm). Impurity molecular OAC [UO2 ]2+ is associated
with uranyl in a silicate glassy phase of hard porcelain and
phosphate glassy phase of bone china.
Impurity OAC are formed by iron group ions — Mn2+,
3+
Cr , and Fe3+, forming characteristic bands in the luminescence spectra of hard and soft porcelain. The luminescence
band in the red region of the spectrum of OAC Fe3+ (lmax ~
716 – 738 nm) was determined in all porcelain samples.
Variations of the position of the center of the Fe3+ band
(lmax ~ 716 – 738 nm) are associated with entry into the Aland Si-tetrahedra. The OAC Mn2+ luminescence band
(lmax ~ 560 – 568 nm) in the yellow-green region of the
spectrum was found only in soft porcelain specimens, and
the OAC Cr3+ band in the red region of the spectrum (lmax ~
716 – 738 nm) in samples of hard and soft porcelain.
Narrow OAC Dy3+ and Sm3+ bands were found only in
samples of soft high-alkaline porcelain.
The high linearity of the ratio of the intensities of the luminescence bands of Fe3+ and [UO2 ]2+ OAC for different
porcelain samples measured with no detection delay and
with detection delay by 180 msec after the laser pulse attests
the stability of the decay kinetics and independence from
band strength.
414
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