Review Article Enhanced Optical Properties of Germanate and...

Hindawi Publishing CorporationThe Scientific World JournalVolume 2013, Article ID 385193, 13 pageshttp://dx.doi.org/10.1155/2013/385193

Review ArticleEnhanced Optical Properties of Germanate and Tellurite GlassesContaining Metal or Semiconductor Nanoparticles

Cid Bartolomeu de Araujo,1 Diego Silvério da Silva,2

Thiago Alexandre Alves de Assumpção,2 Luciana Reyes Pires Kassab,3

and Davinson Mariano da Silva3

1 Departamento de Fısica, Universidade Federal de Pernambuco, 50740-540 Recife, PE, Brazil2 Departamento de Engenharia de Sistemas Eletronicos, Escola Politecnica da USP, 05508-900 Sao Paulo, SP, Brazil3 Laboratorio de Tecnologia em Materiais Fotonicos e Optoeletronicos, Faculdade de Tecnologia de Sao Paulo, CEETEPS/UNESP,01124-060 Sao Paulo, SP, Brazil

Correspondence should be addressed to Luciana Reyes Pires Kassab; [email protected]

Received 14 December 2012; Accepted 17 January 2013

Academic Editors: R. Pode, P. D. Sahare, and D. Zhang

Copyright © 2013 Cid Bartolomeu de Araujo et al. This is an open access article distributed under the Creative CommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

Germanium- and tellurium-based glasses have been largely studied due to their recognized potential for photonics. In this paper,we review our recent studies that include the investigation of the Stokes and anti-Stokes photoluminescence (PL) in different glasssystems containing metallic and semiconductor nanoparticles (NPs). In the case of the samples with metallic NPs, the enhancedPL was attributed to the increased local field on the rare-earth ions located in the proximity of the NPs and/or the energy transferfrom the metallic NPs to the rare-earth ions. For the glasses containing silicon NPs, the PL enhancement was mainly due to theenergy transfer from the NPs to the Er3+ ions. The nonlinear (NL) optical properties of PbO-GeO

2films containing gold NPs were

also investigated. The experiments in the pico- and subpicosecond regimes revealed enhanced values of the NL refractive indicesand large NL absorption coefficients in comparison with the films without gold NPs. The reported experiments demonstrate thatgermanate and tellurite glasses, having appropriate rare-earth ions doping and NPs concentration, are strong candidates for PL-based devices, all-optical switches, and optical limiting.

1. Introduction

Suitable composites for photonic applications have to presentlarge transmittance, high refractive index, low cut-off phononenergy, and large nonlinear optical response. Germanate andtellurite glasses have these characteristics and were identifiedas good hosts for trivalent rare-earth ions (REI) and metal orsemiconductor nanoparticles (NPs) [1–12]. In these glasses,the linear and nonlinear optical properties may be largelyenhanced due to the presence of the NPs. Specifically, inglasses containing metal NPs when the incident light or thephotoluminescence (PL) wavelengths are near the localizedsurface plasmon resonance (LSPR) wavelength, 𝜆SP, a largePL enhancement may occur. In principle, 𝜆SP depends onthe host and metal dielectric functions as well as on the

dimensions and shape of the NPs. The PL efficiency of acomposite for a given incident wavelength depends on theLSPR, the NPs concentration, and the density of phononstates in the host material. In particular, REI doped glassescontaining metallic NPs have been investigated because theirluminescence may be intensified by energy transfer from themetallic NPs and/or due to enhancement of the local fieldthat acts on the REI located in the proximity of the NPs[10, 11]. On the other hand, glasses containing silicon NPs(semiconductor quantumdots)may act as efficient absorbers,and the energy stored in the Si NPs may be transferred toREI, and thus they may contribute for PL enhancement invarious wavelengths ranges that can be selected controllingthe quantum dots sizes. Some evidence of this effect wasreported long ago for silicon-rich silica glass [13–16].

2 The Scientific World Journal

Table 1: Composition and parameters used for production of the glass samples. M/A refer to melting/annealing.

Sample Glass composition (wt.%) Dopants (wt.%) M/A temperature (∘C) M/A time (h)PGO-Er/Yb:Ag 40.3GeO2-59.7PbO 0.5Er2O3-3.0Yb2O3-1.0AgNO3 1200/420 1/2PGO-Eu:Ag 40.3GeO2-59.7PbO 0.5Eu2O3-3.0AgNO3 1200/420 1/3BGO-Eu:Au 58.4GeO2-41.6Bi2O3 0.5Eu2O3-3.0Au2O3 1100/420 1/3BGO-Er:Si 58.4GeO2-41.6Bi2O3 0.5Er2O3-0.2Si nanopowder 1100/420 1/3TZO-Er:Ag 85.0TeO2-15.0ZnO 0.5Tm2O3-2.0AgNO3 800/325 20/2TWB-Er:Ag 54.5TeO2-22.6WO3-22.7Bi2O3 1.0Er2O3-2.0AgNO3 760/360 45/1

The first report on nucleation of silver NPs in germanateglasses (PbO-GeO

2) was presented in [17], whereas the

possibility of production of silver NPs in tellurite glasses waspublished for the first time in [18]. Also it was reported forthe first time the nucleation of copper NPs in PbO-GeO

2

thin films for applications in all-optical switching [19]. Thevarious studies reported for germanate and tellurite glasses,with metallic NPs and different REI, demonstrated the largepotential of these materials for photonic applications. On theother hand, the influence of Si NPs on the PL properties ofglasses remains a unexploited subject. Recently, we developeda procedure to nucleate Si NPs in germanate glasses thatwas very efficient to improve the PL properties of germanateglasses.

In this paper, we review recent experiments based on thenucleation of Ag, Au, and Si NPs in germanate and telluritebulk glasses containing REI and discuss the optical behaviorof the samples under different excitation conditions. Besidestheworkwith bulk samples, the production of germanate thinfilms using the radio-frequency sputtering technique is alsoreported.The nucleation of goldNPs in the films is described,and a study of the NPs influence on the films’ nonlinearoptical properties is presented.

The paper is organized as follows. In Section 2, wedescribe the fabrication methods and the characterizationtechniques used to study the samples. In Section 3, thestructural characteristics of the samples as well as theiroptical characteristics are discussed. Finally in Section 4, wecomment on the perspectives of applications for the kind ofcomposites discussed here.

2. Methods

2.1. Production of the Bulk Samples. Germanate (GeO2-

PbO and GeO2-Bi2O3) and telurite (TeO

2-ZnO and TeO

2-

WO3-Bi2O3) glasses were prepared with high-purity reagents

(99.999%) using the melt-quenching method followed byadequate heat treatment (HT) that depends on the transitiontemperature of each glass composition. The compositionsstudied are shown in Table 1 as well as the parameters usedin the fabrication process.

The reagents were melted in crucibles made of platinum(for the tellurite glasses) or alumina (for the germanates).Mechanical stirring during the melting was applied to ger-manate glasses, to optimize transparency and homogeneity.After cooling to room temperature inside the furnace, thesamples were polished, cut, and then submitted to additional

HT to nucleatemetallic NPs (metallic ions Ag+ andAu+ fromAgNO

3and Au

2O3are reduced to Ag0 and Au0, resp., for

nucleation of the NPs). Samples without metallic NPs werealso fabricated to be used as reference.

The melt-quenching technique was also used for thefabrication of the samples with silicon quantum dots mixingSi nanograins having average diameter of 100 nm with thebase germanate glass constituents.The starting reagents weremelted inside an alumina crucible for 1 h at 1200∘C, quenchedin air in a preheated brass mold, and annealed at 420∘Cto minimize internal stress. Finally, the glasses were cooledto room temperature inside the furnace. After cooling, thesamples’ surfaces were polished to optical quality. Sampleswithout Si-NCs and doped with Er3+ were also fabricatedto be used as reference. Transparent glasses stable againstcrystallization were produced. The density of Si-NCs wascontrolled by heat-treating the samples for time intervals of3, 48, and 72 hours, at 420∘C.

2.2. Production of the Thin Film Samples. The production ofnoncrystalline films with and without gold NPs was madeby RF sputtering (at 13.56MHz) under 5.0mTorr of argon.For the glass target preparation, the oxide powders weremixed and then submitted to 8 tons uniaxial press. Then,sinterization at 750∘C, for 10 h, was performed followed byHT at 370∘C, at room atmosphere. The films without NPswere prepared using a target with the composition 40GeO

2-

60PbO (in wt%). The films with gold NPs were preparedusing the same glass target and a metallic gold target (purityof 99.99%). The two targets were simultaneously sputtered.The films were deposited on silica substrates placed 15 cm farfrom the targets. The RF power applied in each target was50W for the GeO

2-PbO target and 6W for the gold target;

the deposition time was set to obtain films with thickness of≈1.0 𝜇m.The HT of the films was performed during differenttimes and temperatures to nucleate the gold NPs.

2.3. Techniques Employed for Characterization of the Samples.To investigate the size and shape of the NPs, a Transmis-sion Electron Microscope (TEM) operating at 200 kV anda high-resolution transmission electron microscope (HR-TEM) operating at 300 kV were used. electron diffractionmeasurements were performed to confirm the crystallinestructure of the NPs.

All optical measurements were made at room tempera-ture.

The Scientific World Journal 3

400 450 500 550 600 650 7000.25

0.5

0.75

1

1.25

1.5

1.75

2

2.25Ab

sorp

tion

spec

trum

(a.u

.)

3h

48h

24h

72h

Wavelength (nm)

Without AgNO3

7F 1

-5D37F 0

-5L 6

7F 0

-5D2

(a)

400 450 500 550 600 650 700

0.25

0.5

0.75

1

Abso

rptio

n sp

ectr

um (a

.u.)

Wavelength (nm)

Without Au2O3

350 750

3h

48h24h

72h

7F 0

-5D1

7F 1

-5D1

7F 0

-5D0

7F 0

-5L 6

7F 0

-5D3

7F 0

-5D2

(b)

Figure 1: Absorption spectra of the Eu3+ doped samples heat-treated during different times. (a) PGO-Eu:Ag. (b) BGO-Eu:Au.Also presented are the spectra of both glasses without metallic NPs[1].

A spectrophotometer that operates in the visible andnear-infrared regions was used to measure the absorptionspectra of the samples.

PL spectra were measured with different kinds of excita-tion sources, depending on the sample. In the case of the Eu3+doped samples, excitation at 405 nm was obtained from a15W xenon lamp followed by a 0.25m monochromatorequipped with a holographic grating and the signals wereanalyzed by a phase fluorometer. For the Er3+ doped samples,a CW 980 nm diode laser and an ytterbium laser operatingat 1050 nm were used. For the Tm3+ doped samples, anNd3+: YVO laser operating at 1047 nm was utilized theacquisition of signals was obtained with a monochromatorwith a photomultiplier connected to a lock-in and a computer.

The nonlinear measurements at 532 nm were made usingthe second harmonic of a Nd: YAG laser (Q-switched andmode-locked), coupled to a pulse selector for experimentswith single pulses of 80 ps at 7Hz. The Z-scan technique

30

25

20

15

10

5

0580 600 620 640 660 680 700

Wavelength (nm)

Without AgNO3

Lum

ines

cenc

e int

ensit

y (a

.u.)

3h

48h24h

72h

5D0-7

F 05D0-7

F 1

5D0-7

F 2

5D0-7

F 3

5D0-7

F 4

(a)

70

60

50

40

30

20

10

0

3h

48h24h

72h

580 600 620 640 660 680 700 720Wavelength (nm)

Without Au2O3Lu

min

esce

nce i

nten

sity

(a.u

.)

5D0-7

F 05D0-7

F 1

5D0-7

F 2

5D0-7

F 3 5D0-7

F 4

(b)

Figure 2: Luminescence spectra of the Eu3+ doped samples heat-treated for different times. (a) PGO-Eu:Ag. (b) BGO-Eu:Au. Alsopresented are the spectra of both glasses without metallic NPs.Excitation wavelength: 405 nm [1].

[20] was used to measure the nonlinear refractive index andnonlinear absorption coefficient of the samples.The responsetime of the nonlinearity was determined by a Kerr gate setup[21] based on a Ti-sapphire laser (800 nm; 76MHz; 150 fs) asthe light source. The signals were processed using a boxcarand a computer.

3. Results

3.1. Luminescence of Bulk PGO-Eu:Ag and BGO-Eu:Au. Theinfluence of the metallic NPs on electric-dipole and mag-netic-dipole transitions of Eu3+ doped germanate glasses wasstudied in PGO-Eu:Au and BGO-Eu:Au samples with variousNPs concentrations and their absorption spectra are shown inthe Figures 1(a) and 1(b).

An absorption band in the blue-yellow region is a strongevidence of the nucleation of a large density of metallic NPs.In Figure 1(a) the band centered at ≈450 nm is attributed tothe LSPR of the silver NPs. Notice that the band amplitudeincreases for longer HT times, indicating that the density ofNPs is also increasing. Figure 1(b) exhibits a broad absorption


25

20

15

10

5

0

405

nm

578

nm

590

nm

614

nm

652

nm

695

nm

5L65D35D25D15D0

7F47F37F27F1

7F0

Ener

gy (1

03cm−1)

Figure 3: Simplified energy levels scheme of Eu3+ ions withindication of the radiative transitions observed. The shaded areaindicates the position of the localized surface plasmon band [1].

(a)

(b)

Figure 4: TEM image of the Eu3+ doped samples: (a) GeO2-PbO

glass with silver NPs heat-treated for 72 hours, (b) GeO2-Bi2O3glass

with gold NPs heat-treated for 24 hours [1].

400 450 500 550

0.2

0.3

0.4

0.5

400 600 800 1000 1200 1400 1600

0.2

0.4

0.6

0.8

1

1.2

Wavelength (nm)

2G9/2

4S3/24F7/2

2H11/2

Annealing time:2h24h

48h72h

Yb3+(2F5/2) + Er3+(4I11/2)

4G9/2

4I9/24I13/2

4F9/2

Abso

rptio

n sp

ectr

um (a

.u.)

Wavelength (nm)

4F3/2 +4F5/2

Figure 5: Absorption spectra of PGO-Er/Yb:Ag glasses containingsilver NPs for different heat-treatment times [2].

band centered at ≈500 nm and a background that extendstoward the near infrared, due to the LSPR of the gold NPsand their aggregates.

PL spectra of the same samples for excitation at 405 nmare shown in the Figures 2(a) and 2(b).

The spectra consist of the 4f-4f transitions associated tothe Eu3+ ions: 5D

0-7F1(585 nm), 5D

0-7F2(614 nm), 5D

0-7F3

(650 nm), and 5D0-7F4(700 nm).The results indicate that the

PL amplitudes are affected by the presence of the metallicNPs, for both samples.

It is clearly noticed that the samples with either silveror gold NPs reach maximum PL enhancement for HTduring 3 hours; for longer HT times, it is observed thequenching of the PL spectra for both samples. This behavioris understood considering that with the increasing of the HTtime, more Eu3+ ions become so near from the NPs thatenergy transfer occurs from the directly excited ions to theNPs. The quenching phenomenon occurs because of short-distance Eu3+-NPs the dipole-dipole interaction between theion and an NP becomes large [22].

A simplified energy diagram of the Eu3+ ion is shown inFigure 3. Notice that the excitation and the PL wavelengthsare near resonance with the LSPR.

Figure 4 shows the TEM images of both samples with adistribution of nearly spherical NPs that contributes to therelatively narrow LSPR bands observed in the absorbancespectra.

In conclusion, we emphasize that nucleation of large con-centrations of silver or gold NPs was obtained in Eu3+ dopedgermanate glasses as illustrated by the strong absorption bandassociated to the LSPR. Notice that the presence of silver or


500 550 600 650 7000

1

2

3

4

5

IIII

II

Wavelength (nm)

Annealing time:2h24h

48h72h

UC

lum

ines

cenc

e int

ensit

y (a

.u.)

(a)

0 10 20 30 40 50 60 70 80

0.7

0.8

0.9

1

Containing AgNO3UCI/UCIIIUCII /UCIIIUCI/UCII

Nor

mal

ized

inte

grat

edin

tens

ity ra

tio

Annealing time (hours)

(b)

Figure 6: (a) Frequency upconversion spectra of the of Er3+/Yb3+ codoped PbO-GeO2glasses containing silver NPs for different heat-

treatment times. (b) Normalized integrated upconversion intensity (UCI: peak centered at 525 nm, UCII: peak centered at 550 nm, and UCIII:peak centered at 662 nm) as a function of the annealing time [2].

Figure 7: TEM images of the samples annealed during 48 h at 420∘C[2].

goldNPs in the glasses produces a large PL enhancement.Ourresults are understood considering the energy transfer pro-cess from themetallicNPs to the ions and the enhancement ofthe confined electromagnetic field in the vicinity of the NPs.The PL intensity enhancement associated to magnetic dipoletransitions (5D

0-7F1) of Eu3+ ions are due to the confined

optical magnetic field. Comparisons of the results for themixed electric-dipole magnetic-dipole transition (5D

0-7F3)

with the relative growth of the 5D0-7F2transition indi-

cate that the influence of optical magnetic field is relevantalso in this case. In other words, although the magneticresponse at optical frequencies is usually weak, the location

20

15

10

5

0 4I15/2

4I13/2

4I11/2

4I9/2

4F9/2

4S3/22H11/2

2F7/2

525

nm550

nm

662

nm

Er3+ Yb3+

980nm

2F7/2

2F5/2

Ener

gy (1

03cm−1)

Figure 8: Energy level diagram of Er3+ and Yb3+ ions illustratingpossible upconversion pathways for Er3+/Yb3+codoped glasses. Thesolid straight lines with upward and down arrows indicate opticaltransitions; dotted lines and wavy arrows denote ET processes andnon-radiative relaxation, respectively [2].

of europium ions in a region where the electromagneticfield is confined contributes for the increase in the signalsassociated to magnetic dipole transitions. Furthermore, the1000% enhancement of the PL corresponding to transition5D0-7F2is a remarkable result [1].

3.2. Energy Transfer and Frequency Upconversion in BulkPGO-Er/Yb:Ag. The energy transfer and frequency upcon-version processes in Yb3+/Er3+ doped PbO-GeO

2glass were

studied in the samples containing silver NPs. The excitationwavelengthwas 980 nm in resonancewith the Yb3+ transition2F7/2

-2F5/2

. The efficient energy transfer from resonantlyexcited Yb3+ to Er3+ and the influence of the Ag NPs con-tributed to large enhancement of the whole upconvertedspectrum. Absorption and emission spectra of the PGO-Er/Yb:Ag samples for differentHT times are shown in Figures5 and 6(a) respectively. Emission bands centered at 525, 550,


400 450 500 550 600 650 700 750 800 850 9000

0.5

1

1.5

2

2.5

3

Wavelength (nm)2h24h

48h72h

3F2,3 3H4Abso

rptio

n sp

ectr

a (a.u

.)

Figure 9: Absorption spectra of TZO-Tm:Ag glasses for differentheat-treatment times [3].

and 662 nm that correspond, respectively, to the transitions2H11/2→4I15/2

, 4S3/2→4I15/2

, and 4F9/2→4I15/2

can beseen in Figure 6(a). Figure 6(b) shows that the relativeintensity of the upconversion bands can be adjusted by anappropriate choice of the HT time that controls the amountof silver NPs formed in the sample.

The LSPR band is not observed in Figure 5 because theamount of silverNPs is not enough to originate a strong band.However, we estimate, with basis on the dielectric function ofsilver [19], that 𝜆SP is located between ≈400 and ≈500 nm,as shown in the Figure 1(a). However, the presence of silverNPs in the samples is confirmed by the TEM images shownin Figure 7.

The emission peaks observed in the spectra of the Fig-ure 6(a) are due the transitions indicated in the simplifiedenergy level diagram for the Er3+ and the Yb3+ ions inFigure 8. The proximity between the green PL wavelengthsand the LSPR favors the PL intensity enhancement. The redemission is also intensified for larger values of annealingtimes and this is attributed to the nucleation of larger silverNPs and aggregates.

The ratio between the integrated intensities of transitionscentered at 525 nm and 550 nm changes from 0.77 (HT ≈ 0 h)to ≈1.0 (HT ≈ 50 h) because the transition at 525 nm is closestto the estimated LSPR wavelength than 550 nm.

In summary, with the present results we demonstratedthe simultaneous exploitation of the enhanced local fieldcontribution due to silver NPs and energy transfer processesbetween two different RE ions in order to control the PLspectrum of the glassy composite material. This approachcan be applied for different RE ions in order to improve theefficiency of luminescent displays.

3.3. Frequency Upconversion in Bulk TZO-Tm:Ag and TWB-Er:Ag. The frequency upconversion properties of Tm3+doped TeO

2-ZnO glasses containing silver nanoparticles was

400 440 480 520 560 600 640 6800

25

50

75

100

125

150

175

200

225

Wavelength (nm)

Lum

ines

cenc

e int

ensit

y (a

.u.)

1G4 →3H6

1G4 →3F4

Without silver NPs2h24h

48h72h

(a)

725 750 775 800 825 850 875 9000

100

200

300

400

500

600

700

800

Wavelength (nm)

Lum

ines

cenc

e int

ensit

y (a

.u.)

3H4 →3H6

Without silver NPs2h24h

48h72h

(b)

Figure 10: Emission spectra of TZO-Tm:Ag glasses for differentheat-treatment times [3].

reported for the first time in [3]. For excitation, we used alaser operating at 1050 nm. The influence of the silver NPs inthe infrared-to-visible and infrared-to-infrared upconversionprocesses associated to the Tm3+ ions was studied. Absorp-tion and emission spectra of the TZO-Tm:Ag samples heat-treated for different HT times are shown in Figures 9 and 10,respectively.

As in the previous case (Section 3.2), the LSPR band is notobserved because the amount of NPs is not enough to show anoticeable band. We estimated that the 𝜆SP of isolated NPs tobe located in the range 400 to 500 nm because PGO and TZOhave dielectric functions of approximate values; the presenceof silver NPs is confirmed by the TEM image presented inFigure 11.


Figure 11: TEM images of the samples heat-treated during 48 h [3].

Ener

gy (103

cm−1)

0

5

10

15

20

25

301D2

1G4

3F2,33H4

3H53F4

3H6Tm3+

477

nm

650

nm800

nm

1050

nm

Figure 12: Simplified energy level diagram of Tm3+ ions withindication of the upconversion pathways and wavelengths [3].

Figure 12 presents a simplified energy diagram for theTm3+ ions with indication of the excitation pathways and thePL transitions observed.

One order of magnitude enhancement is observed forthe whole PL spectra that is a remarkable result. The spectracorresponding toHTduring 72 hours showpartial quenchingof the PL intensity as reported for other samples.

The dependence of the upconversion signals with thelaser intensitywas analyzed to identify the routes correspond-ing to each upconversion emission. The log-log plots of theupconversion intensities corresponding to transitions 1G

4→

3H6, 1G4→3F4and 3H

4→3H6present slopes of≈2.7,≈2.8,

450 500 550 600 650 700 750 800 850 900 950 10000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Wavelength (nm)Without Ag NPs1h24h

48h72h

4F3/2 +4F5/2

4F7/2

2H11/2

4S3/2 4F9/2 4I9/24I11/2

Abso

rptio

n sp

ectr

a (a.u

.)

Figure 13: Absorption spectra of TBW-Er:Ag glasses for differentheat-treatment times [4].

Without Ag NPs1h24h

48h72h

500 550 600 650 7000

0.03

0.06

0.09

0.12

0.15

0.18

0.21

0.24

0.27

640 660 6800

0.005

0.01

0.015

Wavelength (nm)

Lum

ines

cenc

e int

ensit

y (a

.u.)

Figure 14: Emission spectra of TBW-Er:Ag glasses for differentheat-treatment times [4].

and≈1.8, respectively.These results indicate that the PL bandsat 477 nm and 650 nm are due to the absorption of threelaser photons, while the transition 3H

4→3H6is due to the

absorption of two photons. Considering the mismatchbetween the incident photon energy and the energy levels,we conclude that the upconversion processes occur becausethe intermediate steps are phonon-assisted. Even the excitedstate absorption 3F

4→3F2,3

which is resonant is followed byemission of phonons due to the decay from level 3F

2,3to the

level 3H4.

The influence of the Ag NPs on the upconversion emis-sion of the TBW-Er:Ag glass was investigated using a laseroperating at 980 nm in resonance with transition 4I

15/2-4I9/2


25

20

15

10

5

0

×103 cm−1

4G9/24G11/22H9/22F3/22F5/22F7/22H11/24S3/24F9/24I9/24I11/2

4I13/2

4I15/2

980

nm

530n

m

547

nm

680

nm

808

nm

854

nm

Ener

gy (c

m−1)

980

nm

Figure 15: Simplified Er energy levels diagram illustrating the-upconversion process by energy transfer and by excited stateabsorption.

0 10 20 30 40 50 60 70 800

0.5

1

1.5

2

2.5

3

3.5

4

530550630

Heat treatment (hours)

Lum

ines

cenc

e int

ensit

y (a

.u.)

Figure 16: Dependence of the upconverted signals on the heattreatment corresponding to 2H

11/2→4I15/2

and 4F9/2→4I15/2

transitions [4].

[4]. Absorption and PL spectra of the samples heat-treatedfor different time intervals are shown in Figures 13 and14, respectively. A simplified Er3+ energy diagram showingpossible process related to the absorption of the laser energyis shown in Figure 15.

By comparing the emission spectra of the sample withoutsilver NPs with the sample heat-treated during 24 h it can beseen that the 2H

11/2→4I15/2

, 4S3/2→ 2 4I

15/2and 4F

9/2→

4I15/2

transitions increased by ≈700%. For HT during 48 hand 72 h, quenching of the PL is observed.The dependence ofthe upconverted intensities exhibited a quadratic dependence

with the laser intensity and the dependence with the HT timeis shown in Figure 16.

Figure 17 shows TEM images of a sample after HT during24 h. The black spots are due to the silver NPs which haveaverage size of about 40 nm. A small amount of silver NPswas observed with average diameter of ≈10 nm. The electrondiffraction pattern is also shown in the inset.

The results presented in this section demonstrate thatthe approach of increasing PL of rare-earth doped telluriteglasses by nucleation of metallic NPs can be successful alsofor this glass family that has proved already its importancefor photonic applications.

3.4. Stokes and Antistokes Luminescence of BGO-Er:Si. Thefirst observation of PL enhancement in BGO-Er:Si excited at980 nmwas reported in [5].The samples fabricated presentedlarge concentration of Si NPs with sizes varying from 2 to10 nm as it is illustrated in Figure 18 for the samples heat-treated during 3 h and 72 h.

Figures 19 and 20 present absorption and emissionspectra of the samples studied including results for a samplewithout Si NPs used as reference sample.The PL signals wereobtained by excitation of transition 4I

15/2-4I9/2

.Absorption bands associated with Er3+ ions are observed

as well as a broad absorption band in the range 450–550 nmthat was ascribed to the electronic transition 2P

1/2→2P3/2

of Bi2+ ions, according to the literature [23, 24]. A partialquenching of the Er3+ transitions 4I

15/2→2H11/2

and4I15/2→4F7/2

due to the presence of the Bi2+ ions can beobserved. However, the quenching is reduced in the samplesheat-treated during longer times.The PL band in the infraredregion, centered at 1530 nm, is due to the 4I

13/2→4I15/2

transition. The Er3+ transitions that correspond to all PLbands are indicated in Figure 15. Note that the signal at545 nm is enhanced by ≈200% for the sample heat-treatedduring 72 hours. For the other emissions centered at 525 nm,660 nm, and 1530 nm, we observed ≈100% enhancementin the PL amplitudes for the samples heat-treated during72 hours. In addition, although the PL spectrum becomesstronger for longer heat-treatment time, the bands’ profiles donot change. These results indicate that a large fraction of theEr3+ ions are located near the interfaces between the Si NPsand the germanatematrix.This is in accordancewith [25] thatshowed a low solubility of Er3+ in Si.

The laser intensity dependence of the visible PL bandsindicates that in the upconversion process two laser photonsare converted to one photon with larger frequency, while thebehavior of the near-infrared emission is a simple downcon-version process involving the absorption of only one laserphoton as illustrated in Figure 21.

Three mechanisms may contribute for the enhancementof the antistokes emission due to the presence of the Si NPs.One mechanism may be the stepwise absorption of laserphotons by the Si NPs with subsequent ET from double-excited Si NPs to Er3+ ions in the ground state. An otherpossible excitation pathway involves ET from two single-photon excited Si NPs to one Er3+ ion initially in the ground


Figure 17: Transmission electron microscope images of TBW-Er:Ag sample with silver NPs after heat-treatment of 24 h [4].

(a)

(b)

Figure 18: TEM images of Si NPs in Er3+ doped GeO2-Bi2O3glasses

heat-treated during 3 h (a) and during 72 h (b) [5].

state. The third possibility is the energy transfer from singleSi NPs to erbium ions already excited by the incident laserto level 4I

11/2. These three processes should be considered

because of the large density of SiNPs in the samples.However,at the present stage of the work, it is not possible to identify

600 800 1000 1200 1400 1600

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

4I13/24I11/2

4I9/2

4F9/2

4S3/2

2H11/24F7/2

Wavelength (nm)

Without Si3h

48h72h

Abso

rptio

n sp

ectr

a (a.u

.)

Figure 19: Absorption spectra of Er3+ doped GeO2-Bi2O3glass

heat-treated during different time intervals to nucleate Si-NPs. Thespectrum of a sample without NPs is shown for reference [5].

the actual mechanism contributing for the upconversionenhancement.

3.5. Third-Order Nonlinearity of PGO:Au Films. In order toexploit the large potential of germanate glasses for integratedoptics, we developed a technique to produce PGO filmscontaining silver NPs [26]. Radiofrequency cosputteringwas used for deposition of noncrystalline films on silicasubstrates. The parameters of the fabrication process and theinfluence of the HT on the optical properties of the filmswere investigated. Good quality PGO films were producedand their nonlinear response was studied. In this section,we report on the third-order optical properties of PGO filmscontaining gold NPs (PGO:Au).

Figure 22(a) shows the absorption spectra of films with-out compensation of the Fresnel reflection contribution.


Without Si-NC3h

48h72h

2H11/2-4

I 15/2

4S 3/2

-4I 15/2

4F 9/2

-4I 15/2

500 550 600 650 700

0.05

0.1

0

Inte

nsity

(a.u

.)

Wavelength (nm)

(a)

Without Si-NC3h

48h72h

4I 15/2

-4I 13/2

1400 1500 1600 1700

0.004

0.008

0.012

0.016

Inte

nsity

(a.u

.)

Wavelength (nm)

(b)

Figure 20: Emission spectra of the Er3+ doped GeO2-Bi2O3glass

with SiNPs heat-treated during different time intervals. (a) Infrared-to-visible frequency upconversion. (b) Frequency downconversion[5].

Notice that while the spectrum of the glass film withoutgold NPs is almost flat along the whole wavelength range,a strong absorption band centered at ≈575 nm (1.96 eV) isobserved in the PGO: Au film due to the LSPR of the goldNPs. Figure 22(b) shows a TEM image of the sample andFigure 22(c) presents the size distribution histogram of theNPs that have average diameter of 16 nm.

Figure 23 shows Z-scan profiles for the films with andwithout gold. The Z-scan technique allows measurementsof the third-order susceptibility of materials [20]. From theclosed aperture Z-scan profile, the amplitude and signal ofthe nonlinear refractive index 𝑛

2are determined. A typical

Z-scan profile of the film with gold is shown in Figure 23(a)indicating a focusing nonlinearity (𝑛

2> 0), while the inset

in the figure shows the result for the film without goldNPs that has negligible nonlinearity. Figure 23(b) shows anopen aperture Z-scan profile for the film with gold NPsand the inset shows negligible nonlinear absorption for thefilm without gold. This measurement allows obtaining thenonlinear absorption coefficient 𝛼

2. The solid lines represent

the theoretical fitting to the experimental data based on theprocedure introduced in [20].

0.6 0.8

1

0.5

1Normalized laser power

Nor

mal

ized

upc

onve

rsio

n in

tens

ity

𝑛: 1

𝑛: 1.9

Figure 21: Integrated luminescence intensity as a function of thelaser intensity [5].

The values of 𝑛2= (6 ± 1) × 10

−10 cm2/W measured at532 nm and 𝛼

2= (1.7±0.3)×10

4 cm/GWare attributed to theNPs contribution, since we did not observe nonlinear signalsin the film without gold. Carbon disulfide (CS

2), in a cell of

1mm length, was used as standard calibration material with𝑛2= 3.1 ×10−14 cm2/W [27].The nonlinear birefringence induced in a pump-probe

experiment using a Kerr gate setup was also studied usinga laser operating at 800 nm (pulses of 150 fs at 76MHz).Figure 24 shows the behavior of the normalized Kerr gatesignal of film with gold NPs as a function of the delay timebetween the pump and probe pulses.

The signal corresponding to CS2, with two decay times: a

fast decay of <50 fs and a slow one of ≈2 ps, is also shown toillustrate the time resolution of the apparatus.The symmetricsignal obtained with the PGO:Au film indicates that thenonlinearity is faster than the laser pulse duration. Also, bymeasuring the behavior of the probe beam signal as a functionof the pump beam intensity, we obtained 𝑛

2= (10 ± 2) ×

10−13 cm2/W. In addition, we investigated the transmittance

of the film as a function of the laser intensity. No changes ofthe transmitted intensity was detected indicating that 𝛼

2was

smaller than the sensitivity of the setup (<60 cm/GW).The nonlinear experiments revealed ultrafast response of

the film with gold NPs and enhanced values of the nonlinearrefractive index at 532 and 800 nm due to the presenceof gold NPs. A large nonlinear absorption coefficient wasmeasured at 532 nm indicating the possible use of the filmsfor optical limiting in the picosecond regime. The HT of thefilms improved the figure of merit for all-optical switching incomparison with the results obtained with the films withoutgold NPs by two orders of magnitude at 800 nm [6].

4. Conclusion

In conclusion, considerable progress has been made overthe last decade on obtaining efficient luminescent compos-ites from germanate and tellurite glasses doped with rare-earth ions containing metallic and semiconductor nanopar-ticles. The work has led to the production of good optical


400 500 600 700 8000

0.5

1

1.5

2

2.5

3

Abso

rban

ce

𝜆 (nm)

Film with goldnanoparticles

PGO glass film

(a)

50nm

(b)

10 12 14 16 18 20 22 24 260

5

10

15

20

25

30

35

Freq

uenc

y (%

)

Particle diameter (nm)

(c)

Figure 22: (a) Absorbance spectra of the PGO film with and without gold NPs at room temperature (films thickness: 1.1 𝜇m). (b) TEM imageof the PGO:Au film. (c) Size distribution histogram of the gold NPs [5].

−15 −10 −5

−15 −10 −5 0 5 10 15

0.6

0.8

1

1.2

1.4

1.6

1.8

Nor

mal

ized

tran

smitt

ance

𝑧 (mm)

0.60.8

11.21.41.6

0 5 10 15

(a)

−15 −10 −5

−15 −10 −5 0 5 10 15

Nor

mal

ized

tran

smitt

ance

0.8

0.9

1

1.1

1.2

1.3

𝑧 (mm)

0 5 10 150.8

0.9

1

1.1

1.2

(b)

Figure 23: Z-Scan traces of the film with gold NPs at 532 nm (open squares). (a) Nonlinear refraction; (b) nonlinear absorption. The resultsfor the film without gold (open circles) are shown in the insets. Laser intensity: 560MW/cm2[27].


−0.5 0 0.5 1 1.5 2 2.5 30

0.2

0.4

0.6

0.8

1

Nor

mal

ized

tran

smitt

ed si

gnal

(a.u

.)

Delay time (ps)

Figure 24: Normalized Kerr gate signal for CS2(open squares) and

for the film with gold NPs (open circles). Laser wavelength: 800 nm.Beams’ intensities: 𝐼pump = 342MW/cm2 and 𝐼probe = 45MW/cm2.[27].

quality samples that present appropriate characteristics forphotoluminescence-based devices.The possibilities to extendthe work towards development of nonlinear optical com-posites are large, and we expect to be successful obtainingefficient materials for nonlinear photonics in the future.

Acknowledgments

This work was supported by the Conselho Nacional deDesenvolvimento Cientıfico e Tecnologico (CNPq) throughthe National Institute of Photonics (INCT Project) and bya grant from CNPq and FACEPE (Fundacao de Amparo aCiencia do Estado de Pernambuco) through the PRONEXprogram.

References

[1] L. R. P. Kassab, D. S. Da Silva, and C. B. de Araujo, “Influence ofmetallic nanoparticles on electric-dipole and magnetic-dipoletransitions of Eu3+ doped germanate glasses,” Journal of AppliedPhysics, vol. 107, no. 11, Article ID 113506, 2010.

[2] L. R. P. Kassab, F. A. Bomfim, J. R. Martinelli, N. U. Wetter, J.J. Neto, and C. B. de Araujo, “Energy transfer and frequencyupconversion in Yb3+-Er3+-doped PbO-GeO

2glass containing

silver nanoparticles,” Applied Physics B, vol. 94, no. 2, pp. 239–242, 2009.

[3] T. A. A. de Assumpcao, D. M. da Silva, M. E. Camilo et al.,“Frequency upconversion properties of Tm3+ doped TeO

2-ZnO

glasses containing silver nanoparticles,” Journal of Alloys andCompounds, vol. 536, supplement 1, pp. S504–S506, 2012.

[4] V. P. P. de Campos, L. R. P. Kassab, T. A. A. de Assumpcao, D. S.da Silva, and C. B. de Araujo, “Influence of silver nanoparticleson the upconversion emission of TeO

2-WO3-Bi2O3glasses

doped with Er3+,” Journal of Applied Physics, vol. 112, Article ID063519, 2012.

[5] D. S. da Silva, L. P. Naranjo, L. R. P. Kassab, and C. B. de Araujo,“Photoluminescence from germanate glasses containing silicon

nanocrystals and erbium ions,” Applied Physics B, vol. 106, no.4, pp. 1015–1018, 2012.

[6] C. B. de Araujo, T. R. Oliveira, E. L. Falcao-Filho, D.M. da Silva,and L. R. P. Kassab, “Nonlinear optical properties of PbO-GeO

2

films containing gold nanoparticles,” Journal of Luminescence,vol. 133, pp. 180–183, 2013.

[7] M. Yamane and Y. Asahara, Glasses for Photonics, CambridgeUniversity Press, Cambridge, UK, 2000.

[8] O. Yasutake, “Recent progress in optics and photonics materialscharacteristics of tellurites glasses as novel fiber raman gainmedia,” Ceramics Japan, vol. 41, no. 9, pp. 698–702, 2006.

[9] M. J. F. Digonnet, Rare Earth Doped Fiber Lasers and Amplifiers,Marcel Dekker, New York, NY, USA, 1993.

[10] L. R. P. Kassab and C. B. de Araujo, “Germanate and telluriteglasses for photonic applications,” in Photonics Research Devel-opments, chapter 13, p. 385, Nova Science, New York, NY, USA,2008.

[11] T. A. A. de Assumpcao, L. R. P. Kassab, A. S. L. Gomes, C. B. deAraujo, and N. U. Wetter, “Influence of the heat treatment onthe nucleation of silver nanoparticles in Tm3+doped PbO-GeO

2

glasses,” Applied Physics B, vol. 103, pp. 165–169, 2011.[12] Y. Chen, Q. Nie, T. Xu, S. Dai, X. Wang, and X. Shen, “A study

of nonlinear optical properties in Bi2O3-WO3-TeO2glasses,”

Journal ofNon-Crystalline Solids, vol. 354, no. 29, pp. 3468–3472,2008.

[13] A. J. Kenyon, P. F. Trwoga,M. Federighi, and C.W. Pitt, “Opticalproperties of PECVD erbium-doped silicon-rich silica: evi-dence for energy transfer between silicon microclusters anderbium ions,” Journal of Physics Condensed Matter, vol. 6, no.21, pp. L319–L324, 1994.

[14] M. Fujii,M. Yoshida, Y. Kanzawa, S. Hayashi, andK. Yamamoto,“1.54 𝜇m photoluminescence of Er3+ doped into SiO

2films

containing Si nanocrystals: evidence for energy transfer fromSi nanocrystals to Er3+,” Applied Physics Letters, vol. 71, no. 9,pp. 1198–1200, 1997.

[15] K. M. Choi, “A chemical strategy to improve the fluorescenceenvironments of erbium-ions doped into organically modifiedhybrid glasses for laser amplifier applications,”Materials Chem-istry and Physics, vol. 103, no. 1, pp. 176–182, 2007.

[16] S. Y. Seo, M. J. Kim, and J. H. Shin, “The Nd-nanocluster cou-pling strength and its effect in excitation/de-excitation of Nd3+luminescence in Nd-doped silicon-rich silicon oxide,” AppliedPhysics Letters, vol. 83, no. 14, pp. 2778–2780, 2003.

[17] L. P. Naranjo, C. B. de Araujo, O. L. Malta, P. A. S. Cruz, and L.R. P. Kassab, “Enhancement of Pr3+luminescence in PbO-GeO

2

glasses containing silver nanoparticles,” Applied Physics Letters,vol. 87, no. 24, Article ID 241914, 2005.

[18] C. B. de Araujo, L. R. Kassab, R. A. Kobayashi, L. P. Naranjo, andP.A. S. Cruz, “Luminescence enhancement of Pb2+ions in TeO

2-

PbO-GeO2glasses containing silver nanostructures,” Journal of

Applied Physics, vol. 99, Article ID 123522, 4 pages, 2006.[19] L. A. Gomez, F. E. P. dos Santos, A. S. L. Gomes, C. B. de

Araujo, L. R. P.Kassab, andW.G.Hora, “Near infrared third nonlinearity of PbO-GeO

2films containing Cu and CuO

2nanopar-

ticles,”Applied Physics Letters, vol. 92, Article ID 141916, 3 pages,2008.

[20] M. Sheik-Bahae, A. A. Said, T. H. Wei, D. J. Hagan, and E. W.Van Stryland, “Sensitive measurement of optical nonlinearitiesusing a single beam,” IEEE Journal of Quantum Electronics, vol.26, no. 4, pp. 760–769, 1990.

[21] Y. R. Shen, Principles of Nonlinear Optics, Wiley, New York, NY,USA, 1984.


[22] P. N. Prasad, Nanophotonics, Wiley, New York, NY, USA, 2004.[23] J. Ren, G. Dong, S. Xu, R. Bao, and J. Qiu, “Inhomogeneous

broadening, luminescence origin and optical amplification inbismuth-doped glass,” Journal of Physical Chemistry A, vol. 112,no. 14, pp. 3036–3039, 2008.

[24] G. Chi, D. Zhou, Z. Song, and J. Qiu, “Effect of optical basicityon broadband infrared fluorescence in bismuth-doped alkalimetal germanate glasses,” Optical Materials, vol. 31, no. 6, pp.945–948, 2009.

[25] D. J. Eaglesham, J. Michel, E. A. Fitzgerald et al., “Microstruc-ture of erbium-implanted Si,”Applied Physics Letters, vol. 58, no.24, pp. 2797–2799, 1991.

[26] D. M. da Silva, L. R. P. Kassab, J. R. Martinelli, and C. B. deAraujo, “Production and characterization of RF-sputteredPbO-GeO

2amorphous thin films containing silver and gold

nanoparticles,” Journal of Non-Crystalline Solids, vol. 356, no.44–49, pp. 2602–2605, 2010.

[27] R. L. Sutherland,Handbook of Nonlinear Optics, Marcel Dekker,New York, NY, USA, 2003.

Submit your manuscripts athttp://www.hindawi.com

ScientificaHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation http://www.hindawi.com Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation http://www.hindawi.com Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials

Review Article Enhanced Optical Properties of Germanate and...

Documents

Transcript of Review Article Enhanced Optical Properties of Germanate and...