- Email: [email protected]
Er3+inverse opals excited at 980 or 808 nm
Journal of Alloys and Compounds 767 (2018) 16e22
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Influence of upconversion luminescence modification on near infrared luminescence and cooperative energy transfer in the YbPO4:Er3þ, Nb3þ/Er3þinverse opals excited at 980 or 808 nm Zhuangzhuang Chai, Zhengwen Yang*, Anjun Huang, Chengye Yu, Jianbei Qiu**, Zhiguo Song College of Materials Science and Engineering, Kunming University of Science and Technology, Kunming, 650093, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 May 2018 Received in revised form 1 July 2018 Accepted 8 July 2018 Available online 9 July 2018
The photoluminescence modification of rare earth ions base on the photonic band gap engineering was extensively reported. In this work, the effect of up-converting luminescence suppression of Er3þ on the near infrared luminescence and cooperative energy transfer from Er3þ to Yb3þ was investigated in the YbPO4 inverse opals single-doped with Er3þ and co-doped with Nd3þ and Er3þ. For the YbPO4:Er3þ inverse opals, when the photonic band gap is overlapped with the green or red up-converting luminescence of Er3þ, the green or red up-converting luminescence of Er3þ was suppressed in the YbPO4:Er3þ inverse opals upon the 980 nm excitation, respectively. It is significative that the enhancement of near infrared luminescence of Er3þ was observed, which is attributed to the electron redistribution in the excited energy levels caused by the upconversion luminescence suppression in the YbPO4:Er3þ inverse opals. For the YbPO4:Nd3þ,Er3þ inverse opals, the green upconversion and near infrared luminescence of Er3þ and the near infrared luminescence of Yb3þ were observed excited at 808 nm. The near infrared luminescence enhancement of Yb3þ was obtained due to the cooperative energy transfer enhancement from Er3þ to Yb3þ caused by the green upconversion luminescence suppression. The result is helpful to learn the relationship between upconversion and infrared luminescence in rare earth ions doped materials. © 2018 Published by Elsevier B.V.
Keywords: Inverse opals Upconversion luminescence Near infrared luminescence Cooperative energy transfer
1. Introduction Rare earth ions doped materials with near infrared (NIR) emission have great application prospects in the fields of the near infrared laser source, optical communication, biosensors and fluorescence immune analysis [1e4]. But the efficiency of near infrared emission of rare earth doped material is low owing to the presence of the competitive relationship between the NIR and upconversion (UC) luminescence, limiting its practical application. Therefore, the modification of UC luminescence may be required in order to obtain the high-efficient NIR luminescence. Photonic crystal is a type of ordered periodical dielectric materials, showing the photonic band gap property [5,6]. The motion of photons could be regulated by the photonic band gap [7], which exhibit the potential
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (Z. Yang), [email protected] (J. Qiu). https://doi.org/10.1016/j.jallcom.2018.07.092 0925-8388/© 2018 Published by Elsevier B.V.
applications in the fields of optical switch, optical filter and optical circuits, etc [8]. In addition, the photonic crystal can modify the spontaneous emission of active centers. The suppression or enhancements of spontaneous emission of active centers embedded in the photonic crystals were reported [9,10]. It is interesting that the photonic crystal can not only modulate the luminescence property of active centers, but also can cause the electron redistribution in the excited energy levels [11]. Thus the photonic crystals modulation provides a possible way to solve the problem of weak near infrared emission of rare earth ions by the modification of UC luminescence. Recently, the UC luminescence modification of rare-earth ions were extensively reported by the photonic crystals [12e14]. For instance, the UC emission suppression of rare earth ions in the region of the photonic band-gap and the enhancement at the photonic band edge were demonstrated in the rare earth ions doped inverse opals, respectively [12]. Additionally, the energy transfer enhancement from the Er3þ to Tm3þ induced by the photonic band gap was obtained, resulting in the enhancement of the
Z. Chai et al. / Journal of Alloys and Compounds 767 (2018) 16e22
short-wavelength UC luminescence [13]. The UC luminescence enhancement of rare earth doped nanoparticles was observed by the surface effect of photonic crystals [14]. Despite achieving many progresses of UC luminescence modification based on the photonic band gap, the influence of the UC luminescence modification on the NIR luminescence and cooperative energy transfer between the rare earth ions was rarely investigated by the photonic crystals. In this work, the YbPO4 inverse opals single-doped with Er3þ and codoped with Nd3þ and Er3þ were prepared by the sol-gel approach. The influence of UC luminescence suppression of Er3þ on the near infrared luminescence and the cooperative energy transfer from Er3þ to Yb3þ was investigated in the YbPO4 inverse opals singledoped with Er3þ and co-doped with Nd3þ and Er3þ, respectively. The enhancement of NIR luminescence property of Er3þ was realized due to the electron redistribution in excited state levels caused by modulating the UC luminescence in the YbPO4:Er3þ inverse opals. The near infrared luminescence enhancement of Yb3þ was observed due to the cooperative energy transfer enhancement from Er3þ to Yb3þ caused by the UC luminescence suppression in the YbPO4:Nd3þ, Er3þ inverse opals. 2. Experimental Three kinds of opal photonic crystals were self-assembled by using 300, 360 and 450 polystyrene (PS) microspheres, respectively, exhibiting the three-dimensional ordered structures. The Yb2O3, Er2O3 and P2O5 as the raw materials were used to prepare the YbPO4:Er3þ inverse opals. The Yb2O3 and Er2O3 were dissolved by the hot HNO3, respectively, and the excess HNO3 was evaporated to obtain ytterbium and erbium nitrification. The P2O5, ytterbium and erbium nitrification dissolved by the hydrous ethanol were mixed. After the stirring for 2 h, the homogeneous transparent YbPO4:Er3þ sol was prepared. The YbPO4:Er3 sol was filled into the voids of three kinds of opal photonic crystals, which was sintered at the 900 C in air. Then the YbPO4:Er3þ inverse opals were prepared. The preparation processes of YbPO4:Nd3þ, Er3þ inverse opals were similar with that of the YbPO4:Er3þ sol except that 1mol % Nd3þ was added into the homogeneous transparent YbPO4:Er3þ sol. The X-ray (XRD) diffractometer was used to characterize the crystallinity and phase purity of YbPO4 inverse opals single-doped with Er3þ and co-doped with Nd3þ and Er3þ. The micro-structures
17
of YbPO4 inverse opals single-doped with Er3þ and co-doped with Nd3þ and Er3þ were characterized by the scanning electron microscope (SEM). The NIR and UC luminescence spectra of YbPO4:Er3þ inverse opals were measured by the FLSP-980 spectrophotometer under the excitation of 980 nm and the NIR and UC luminescence spectra of YbPO4:Nd3þ, Er3þ inverse opals were measured excited at the 808 nm. The excitation power of 808 and 980 nm was 1.7 W. The photonic band gap property of YbPO4 inverse opal was characterized by the absorption spectra (Hitachi U4100 spectrophotometer). The decay curves of UCL were characterized by the FLSP-980 spectrophotometer. 3. Results and discussion 3.1. Influence of upconversion luminescence modification on near infrared luminescence in the YbPO4:Er3þ inverse opals excited at the 980 nm The YbPO4:Er3þ inverse opals prepared by the 300, 360 and 450 nm opals were designated as the IPC-I, IPC-II and IPC-III, respectively. Fig. 1 (a) presented the XRD patterns of YbPO4:Er3þ inverse opals prepared by the 300, 360 and 460 nm opal templates and the standard PDF card (NO.43-0530). The XRD diffraction peaks of YbPO4 inverse opals without and with the doping of Er3þ can be indexed by the standard PDF card, suggesting the preparation of monoclinic YbPO4:Er3þ inverse opals. The Debye-Scherer equation was applied to calculate the grain size of YbPO4 in the IPC-I, IPC-II and IPC-III, which were about 76.6, 72.2 and 75.3 nm, respectively. Fig. 1 (b)-(d) presented the SEM images of opals self-assembled by the 300, 360 and 450 nm PS microspheres, respectively, showing the ordered structures with face centered cubic close packing. The SEM images of the IPC-I, IPC-II and IPC-III were exhibited in the Fig. 1 (e)-(g). The YbPO4:Er3þ inverse opals replicated the reverse structure of opal templates, having a long range order in threedimensional space. The center to center distance between the two near air-spheres of IPC-I, IPC-II and IPC-III was obtained according to the SEM images exhibited in Fig. 1, which was about 227, 280, and 336 nm, respectively. In comparison with the size of raw PS microspheres, the shrinkage of about 24.3%, 22.2% and 26.3% was observed for the IPC-I, IPC-II and IPC-III after the calcination, respectively.
Fig. 1. The XRD patterns (a) of IPC-I, IPC-II and IPC-III; the SEM images of opals self-assembled by the 300 (b), 360 (c) and 450 nm (d) PS microspheres; the SEM images of IPC-I (e), IPC-II (f) and IPC-III (g).
18
Z. Chai et al. / Journal of Alloys and Compounds 767 (2018) 16e22
Fig. 2 exhibited the UVevisible absorption spectra of IPC-I, IPC-II and IPC-III. The obvious absorption peak at the 420, 540 and 645 nm was observed in the IPC-I, IPC-II and IPC-III, respectively, which was caused by the Bragg diffraction of ordered structure of inverse opals. The center to center distance (D) between the two near air-spheres for the IPC-I, IPC-II and IPC-III was calculated by using the refractive index (neff) and photonic band gap position (l) of YbPO4 inverse opal and based on the Bragg equation and Snell's law [14]:
Fig. 2. The absorption spectra of IPC-I, IPC-II and IPC-III
r ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi n2eff sin2 q
(1)
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi n2 f þ n2air ð1 f Þ
(2)
l ¼ 1:633D
neff ¼
where nair, n and q denotes as the refractive indexes of air (1), YbPO4 (1.68 obtained at about 500 nm) [15], and the angle between the normal line of inverse opal and the incidence light, respectively. For the inverse opal with close packing face centered cubic structure, the volume fraction of YbPO4 is about 26%. The center to center distance (D) of two near air-spheres for the IPC-I, IPC-II and IPC-III was calculated to be about the 231, 278 and 333 nm, respectively, which is coincident with these obtained by the SEM images. Fig. 3 (a) and (b) show the UC luminescence spectra of IPC-I, IPCII and IPC-III upon the 980 nm excitation. The 524, 548, and 660 nm UC luminescence was observed, corresponding to the 2H11/2 / 4I15/ 4 4 4 4 3þ 2, S3/2 / I15/2 and F9/2 / I15/2 of Er , respectively [16]. It is noted that the photonic band gap of the IPC-II and IPC-III was located at about 540 and 645 nm, respectively, which is overlapped with the 524/548 nm green and 660 nm red UC luminescence. The 524/548 and 660 nm UC luminescence is suppressed in the IPC-II and IPC-III, respectively, in comparison with the IPC-I, which is a typical modulation phenomenon of UC luminescence caused by the photonic band gap [11]. The NIR pump power dependence of UC luminescence intensity can be used to characterize the UC mechanism. It is well-known that the UC luminescence intensity Iup is proportional to the NIR excitation power (P), which can be
Fig. 3. The UC luminescence of the IPC-I/IPC-II (a) and IPC-II/IPC-III (b) upon the 980 nm excitation; the UC luminescence intensity of IPC-I as a function of excitation power (c); the UC luminescence mechanism of YbPO4:Er3þ inverse opals (d).
Z. Chai et al. / Journal of Alloys and Compounds 767 (2018) 16e22
expressed as IupfPn. In the IupfPn equation, the n is the photon numbers absorbed by the Er3þ in the UC luminescence process. The UC luminescence intensity of the IPC-I was measured as a function of the excitation power, as shown in the Fig. 3 (c), which exhibited that the red and green UC luminescence was attributed to the two photons processes. Fig. 4 (b) shows the UC luminescence mechanism of YbPO4:Er3þ inverse opals under the excitation of 980 nm. The energy transfer (ET) from Yb3þ to Er3þ ions excited the Er3þ ions, resulting in the population of 4I11/2 state. The electrons at the 4 I11/2 state jumped to the 4F7/2 level by the further ET excitation. The electrons at the 4F7/2 state relaxed non-radiatively to the near 4S3/2 and 2H11/2 levels. The 2H11/2/4S3/2 / 4I15/2 radiative transitions lead to the generation of the 524/548 nm UC luminescence. For the 660 nm UC luminescence, the non-radiative relaxation of the 4I11/2 level populated the 4I13/2 level. The electrons at the 4I13/2 state jumped to the 4F9/2 levels by the further ET excitation. In addition, the electrons at the 2H11/2/4S3/2 states can relax non-radiatively to the 4F9/2 level. Thus the 4F9/2 / 4I15/2 transition generates the 660 nm UC luminescence. The NIR luminescence spectra of YbPO4:Er3þ inverse opals were measured upon the 980 nm excitation, as shown in Fig. 4 (a) and (b). The NIR luminescence peak centered at 1550 nm ranging from 1450 to 1600 nm was observed in the IPC-I, IPC-II and IPC-III, which
Fig. 4. The NIR luminescence spectra of IPC-I/IPC-II (a) and IPC-I/IPC-III (b) upon the 980 nm excitation.
19
is corresponding to the transition from 4I13/2 to 4I15/2 of Er3þ. As shown in Fig. 3(d), the 4I13/2 / 4I15/2 radiative transition results in the generation of the NIR luminescence centered at 1550 nm ranging from 1450 to 1600 nm. It is interesting that the NIR luminescence in the IPC-II and IPC-III was enhanced in contrast to the IPC-I because of the UC luminescence modification caused by the photonic band gap. As shown in Fig. 3 (d), the electrons located at the 4F9/2, 2H11/2 and 4S3/2 excitation state can loss their energy by the two paths: the non-radiative relaxation form 4F9/2, 2H11/2 and 4 S3/2 levels to the 4I13/2 level or the UC luminescence transition from 4 F9/2, 2H11/2 and 4S3/2 to 4I15/2 ground state. The UC luminescence from the 4S3/2/2H11/2 and 4F9/2 to 4I15/2 ground state compete with the non-radiative relaxation form 4F9/2, 2H11/2 and 4S3/2 levels to the 4 I13/2 level. The inhibition of UC luminescence from the 4F9/2 and 4 S3/2/2H11/2 to 4I15/2 ground state in the YbPO4:Er3þ inverse opals can cause the enhancement of non-radiative relaxation from the 4 F9/2 and 4S3/2/2H11/2 to 4I13/2 state. As a result, the enhancement of NIR luminescence from the 4I13/2 / 4I15/2 radiative transition in the IPC-II and IPC-III were observed in contrast to the IPC-I. 3.2. Influence of upconversion luminescence modification on cooperative energy transfer in the YbPO4:Nb3þ/Er3þinverse opals excited at the 808 nm Two kinds of YbPO4:Nd3þ,Er3þ inverse opals were prepared by filling the YbPO4:Nd3þ, Er3þ sol into the opal templates selfassembled by the 300 and 360 nm polystyrene (PS) microspheres. The YbPO4:Nd3þ, Er3þ inverse opals prepared by the 300 and 360 nm opal templates were designated as the IPC-IV and IPC-V, respectively. Fig. 5 presented the XRD patterns and SEM images of the IPC-IV and IPC-V. The YbPO4:Nd3þ, Er3þ inverse opals are the monoclinic phase regarding of the size of PS microspheres, exhibiting an order structure. The doping of Nd3þ has no influence on the phase and order structure of YbPO4:Er3þ inverse opals. The grain size of YbPO4 for the IPC-IV and IPC-V calculated by the Scherer equation based on the XRD patterns was about the 77.1 and 74.8 nm, respectively. According to the SEM images shown in Fig. 5, the center to center distance between the near two air-spheres for the IPC-IV and IPC-V was about 230 and 276 nm, respectively. Compared with raw size of PS microspheres, the shrinkage of about 23.6 and 23.1% was obtained for the IPC-IV and IPC-V after the hightemperature calcination, respectively. Fig. 6 (a) showed the absorption spectra of IPC-IV and IPC-V. The photonic band gap caused by the Bragg diffraction of ordered structure for the IPC-IV and IPC-V was located at the 420 and 543 nm, respectively. The center to center distance (D) between the two near air-spheres of IPC-IV and IPC-V was calculated by the Bragg equation and Snell's law, which was about the 228 and 280 nm, respectively. The calculated results are coincident with these obtained by the SEM images. Fig. 6 (b) shows the UC luminescence spectra of IPC-IV and IPC-V upon the 808 nm excitations, exhibiting the 524 and 548 nm UC luminescence, which is corresponding to the 2H11/2 / 4I15/2 and 4S3/2 / 4I15/2 of Er3þ, respectively. The suppression of 524 and 548 nm UC luminescence is observed in the IPC-V in contrast to the IPC-IV due to the typical photonic band gap effect [17]. The 808 nm NIR pump power dependence of UC luminescence intensity for the IPC-IV was shown in the Fig. 6 (c), which exhibited that the green UC luminescence was from the two photons processes. The UC luminescence spectra of the IPC-I～III inverse opals without the Nd3þ doping were measured upon the 808 nm excitations, as shown in Fig. S1 of supporting information. No green UC luminescence of Er3þ was observed for the IPC-I～III inverse opals without the Nd3þ doping, which suggested that the green UC luminescence of Er3þ of IPC-IV and IPC-V is related to the Nd3þ doping upon the 808 nm
20
Z. Chai et al. / Journal of Alloys and Compounds 767 (2018) 16e22
Fig. 5. The XRD patterns (a) of the IPC-IV and IPC-V; the SEM images of IPC-IV(b) and IPC-V(c).
Fig. 6. The absorption spectra of IPC-IV and IPC-V(a); the UC luminescence spectra of the IPC-IV and IPC-V (b) upon the 808 nm excitation; the UC luminescence intensity of IPC-IV as a function of excitation power (c); the UC luminescence mechanism of YbPO4:Nd3þ, Er3þ inverse opals (d).
excitations. The UC luminescence mechanism of YbPO4: Nd3þ, Er3þ inverse opals was provided under the excitation of 808 nm, as shown Fig. 6 (d). The Nd3þ was excited to the 4F5/2 state from the ground state under the excitation of 808 nm. The energy transfer (ET) from Nd3þ to Yb3þ ions excited the Er3þ ions, populating the 2 F5/2 state of Yb3þ ions. The two-steps energy transfer (ET) from Yb3þ to Er3þ populated the 2H11/2/4S3/2 levels of Er3þ. The 2H11/2/4S3/ 4 2 / I15/2 radiative transitions produce the 524/548 nm UC
luminescence. Fig. 7 exhibited the NIR luminescence spectra of YbPO4: Nd3þ, 3þ Er inverse opals upon the 808 nm excitations. The NIR luminescence ranging from 1450 to 1600 nm in the IPC-IV and IPC-V is from the transition from 4I13/2 to 4I15/2 of Er3þ, as shown in Fig. 3 (d). The NIR luminescence ranging from 925 to 1050 nm was attributed to the 2F5/2 / 2F7/2 radiative transition of Yb3þ. In order to obtain the NIR luminescence mechanism of Yb3þ, the NIR spectrum of IPC-I
Z. Chai et al. / Journal of Alloys and Compounds 767 (2018) 16e22
Fig. 7. The near-infrared luminescence spectra (a, b) of the IPC-I, IPC-IV and IPC-V upon the 808 nm excitation, the decay curves of 548 nm UC luminescence (c) of IPCIV and IPC-V upon the 808 nm excitation.
inverse opal without the Nd3þ doping was measured upon the 808 nm excitations, as shown in Fig. 7 (a). It is noted that no NIR luminescence of Yb3þ was observed for the IPC-I inverse opal without the Nd3þ doping, which suggested that the NIR luminescence of Yb3þ is attributed to the energy transfer from the Nd3þ to Yb3þ. The energy transfer (ET) from Nd3þ to Yb3þ ions excited the Er3þ ions, populating the 2F5/2 state of Yb3þ ions. The radiative transition from 2F5/2 state to ground state results in the NIR luminescence of Yb3þ. In addition, it is reported that the cooperative energy transfer from the Er3þ to 2Yb3þ can cause the NIR luminescence of Yb3þ [18], and the cooperative energy transfer was expressed as the 4S3/2/2H11/2 (Er3þ)/22F5/2 (Yb3þ), as shown in
21
Fig. 6 (d). The NIR luminescence ranging from 1450 to 1600 nm in the IPCV was enhanced upon the 808 nm excitation in contrast to the IPCIV because of the green UC luminescence suppression caused by the photonic band gap. The enhancement mechanism of NIR luminescence ranging from 1450 to 1600 nm of YbPO4: Nd3þ, Er3þ inverse opals upon the 808 nm excitation is similar with that of YbPO4: Er3þ inverse opals upon the 980 nm excitation. The inhibition of green UC luminescence from 4S3/2/2H11/2 to 4I15/2 ground state in the YbPO4: Nd3þ, Er3þ inverse opals can cause the enhancement of non-radiative relaxation from the 4S3/2/2H11/2 to 4 I13/2 state, result in the NIR luminescence enhancement for the IPC-V. It is interesting that the NIR luminescence ranging from 925 to 1050 nm of Yb3þ was enhanced in the IPC-V in contrast to the IPCIV. The NIR luminescence of Yb3þ are attributed to the two mechanisms: the energy transfer from Nd3þ to Yb3þ ions and the cooperative energy transfer from the Er3þ to 2Yb3þ. The energy transfer from Nd3þ to Yb3þ ions was not influence by photonic band gap because the absorption and luminescence of Nd3þ and Yb3þ ions is apart from the photonic band gap [19]. The enhancement of NIR luminescence of Yb3þ is attributed to the enhanced cooperative energy transfer from the Er3þ to 2Yb3þ. The 2H11/2 and 4S3/2 excitation state can loss their energy by the two paths: the cooperative energy transfer from the Er3þ at 4S3/2/2H11/2 excited state to 2Yb3þ or the UC luminescence transitions from 2H11/2 and 4S3/2 to 4I15/2 ground state. The UC luminescence from the 4S3/2/2H11/2 to 4I15/2 ground state compete with the cooperative energy transfer from the Er3þ at 4S3/2/2H11/2 excited state to 2Yb3þ. The inhibition of UC luminescence from the 4S3/2/2H11/2 to 4I15/2 ground state in the YbPO4:Nd3þ,Er3þ inverse opals can cause the enhancement of the cooperative energy transfer from the Er3þ to 2Yb3þ. As a result, the NIR luminescence enhancement of Yb3þ for the IPC-V was observed in contrast to the IPC-IV. In order to demonstrate the enhancement of cooperative energy transfer from the Er3þ to 2Yb3þ, the decay curves of 548 nm UC luminescence of IPC-IV and IPC-V inverse opals was measured upon the 808 nm excitation, as shown in Fig. 7 (c). The UC luminescence decay curves of rare earth ions doped phosphors can be described by single or double exponential equation due to the occupation of various sites of RE ions in the host []. In present work, the photonic band gap has an influence on the decay lifetimes of Er3þ ions, which result in that the decay curves were not fitted by the single exponential equation. Therefore, the decay curves were fitted by using a double exponential equation. It can be seen that the in the UC decay lifetime of 548 nm UC luminescence in the IPC-V inverse opal was decreased in contrast to that of the IPC-IV inverse opal. It is well-known that the photonic band gap can cause the increasing or no changing of UC decay lifetime when the photonic band gap is overlapped with the luminescence peak [20]. In the present work, the UC decay lifetime of 548 nm UC luminescence in the IPC-V inverse opal was decreased in contrast to that of the IPC-IV inverse opal although the photonic band gap of IPC-V inverse opal is overlapped with the 548 nm UC luminescence, which is caused by the enhancement of the cooperative energy transfer from the Er3þ to 2Yb3þ. 4. Conclusions The YbPO4 inverse opals single-doped with Er3þ and co-doped with Nd3þ and Er3þ were prepared by the sol-gel approach. The influence of upconversion luminescence modification of Er3þ on the near infrared luminescence was investigated in the YbPO4:Er3þ inverse opals. The green, red upconversion luminescence and near infrared luminescence were observed in the YbPO4:Er3þ inverse opals upon the 980 nm excitation. The near infrared luminescence
22
Z. Chai et al. / Journal of Alloys and Compounds 767 (2018) 16e22
of Er3þ was enhanced when the photonic band gap is overlapped with the green or red up-converting luminescence of Er3þ, which is attributed to the electron redistribution in the excited energy levels caused by the upconversion luminescence suppression in the YbPO4:Er3þ inverse opals. The influence of upconversion luminescence modification of Er3þ on the cooperative energy transfer from Er3þ to 2Yb3þ was observed in the YbPO4:Nd3þ, Er3þ inverse opals upon the 808 nm excitations. The cooperative energy transfer enhancement from Er3þ to 2Yb3þ was enhanced due to the upconversion luminescence suppression of Er3þcaused by the photonic band gap effect, resulting in the enhancement of near infrared luminescence of Yb3þ. Acknowledgments This work was supported by the National Natural Science Foundation of China (51762029), and the Applied basic research key program of Yunnan Province. Appendix A. Supplementary data Supplementary data related to this article can be found at https://doi.org/10.1016/j.jallcom.2018.07.092. References [1] D.K. Chatteriee, A.J. Rufalhah, Y. Zhang, Upconversion fluorescence imaging of cells and small animals using lanthanide doped nanocrystals, Biomaterials 29 (2008) 937e943. [2] S. Heer, K. Kompe, H.U. Gudel, M. Haase, Highly efficient multicolour upconversion emission in transparent colloids of lanthanide-doped NaYF4 nanocrystals, Adv. Mater. 16 (2004) 2102e2105. [3] C. Klein, M.K. Nazeeruddin, P. Liska, D. Di Censo, N. Hirata, E. Palomares, J.R. Durrant, M. Gratzel, Engineering of a novel ruthenium sensitizer and its application in dye-sensitized solar cells for conversion of sunlight into electricity, Inorg. Chem. 44 (2005) 178e180. [4] H. Lin, D.Q. Chen, Y.L. Yu, Z.F. Shan, P. Huang, Y.S. Wang, J.L. Yuan, Nd3þsensitized upconversion white light emission of Tm3þ/Ho3þTm3þ/Ho3þbridged by Yb3þ in b-YF3 nanocrystals embedded transparent glass ceramics, J. Appl. Phys. 107 (2010), 103511. [5] S. Xu, W. Xu, Y.F. Wang, S. Zhang, Y.S. Zhu, L. Tao, L. Xia, P.W. Zhou, H.W. Song, NaYF4:Yb,Tm nanocrystals and TiO2 inverse opal composite films: a novel device for upconversion enhancement and solid-based sensing of avidin,
Nanoscale 6 (2014) 5859e5870. [6] Y.D. Yang, P.W. Zhou, W. Xu, S. Xu, Y.D. Jiang, X. Chen, H.W. Song, NaYF4: Yb3þ,Tm3þ inverse opal photonic crystals and NaYF4:Yb3þ,Tm3þ/TiO2 composites: synthesis, highly improved upconversion properties and NIR photoelectric response, J. Mater. Chem. C 4 (2016) 659e662. [7] M.O.A. Erola, A. Philip, T. Ahmed, S. Suvanto, T.T. Pakkanen, Fabrication of Auand Ag-SiO2 inverse opals having both localized surface plasmon resonance and Bragg diffraction, J. Solid State Chem. 230 (2015) 209e217. [8] B.T. Holland, C.F. Blanford, T. Do, A. Stein, Synthesis of highly ordered, threedimensional, macroporous structures of amorphous or crystalline inorganic oxides, phosphates, and hybrid composites, Chem. Mater. 11 (1999) 795e805. [9] S.F. Lai, Z.W. Yang, J. Li, B. Shao, J.Z. Yang, Y.D. Wang, J.B. Qiu, Z.G. Song, Photoluminescence enhancement of Eu3þ ions by Ag species in SiO2 threedimensionally ordered macroporous materials, J. Mater. Chem. C 3 (2015) 7699e7708. [10] H.B. Sun, S. Matsuo, H. Misawa, Three-dimensional photonic crystal structures achieved with two-photon-absorption photopolymerization of resin, Appl. Phys. Lett. 74 (1999) 786e788. [11] Z.D. Liu, Z.W. Yang, L. Sun, B. Li, J. Zhou, Energy transfer enhancement in Eu3þ, Tb3þ-Doped SiO2 inverse opal photonic crystals, J. Am. Ceram. Soc. 94 (2011) 2731e2734. [12] Z.Z. Chai, Z.W. Yang, A.J. Huang, C.Y. Yu, J.B. Qiu, Z.G. Song, Preparation and upconversion luminescence modification of YbPO4:Er3þ inverse opal heterostructure, J. Rare Earths 35 (2017) 1180e1185. [13] V.A.G. Rivera, M. El-Amraoui, Y. Ledemi, Y. Messaddeq, E. Marega, Expanding broadband emission in the near-IR via energy transfer between Er3þ-Tm3þ codoped tellurite-glasses, J. Lumin. 145 (2014) 787e792. [14] J.Y. Liao, Z.W. Yang, S.F. Lai, B. Shao, J. Li, J.B. Qiu, Z.G. Song, Y. Yang, Upconversion emission enhancement of NaYF4:Yb,Er nanoparticles by coupling silver nanoparticle plasmons and photonic crystal effects, J. Phys. Chem. C 118 (2014) 17992e17999. [15] H. Lin, D.Q. Chen, M.T. Niu, Y.L. Yu, P. Huang, Y.S. Wang, Synthesis and upconversion emission of rare earth-doped olive-like YF3 micro-particles, Mater. Res. Bull. 45 (2010) 52e55. [16] Z. Khadraoui, K. Horchani-Naifer, M. Ferhi, M. ferid, Synthesis, characterization and DFT calculation of electronic and optical properties of YbPO4, Chem. Phys. 457 (2015) 37e42. [17] J.Q. Wang, C.W. Zhou, L. Su, X.Y. Ji, X.B. Chen, M. Zhang, Preparation of inverse opal cerium dioxide for optical properties research, Mater. Lett. 158 (2015) 123e127. [18] L.N. Guo, Y.H. Wang, W. Zeng, L. Zhao, L.L. Han, Band structure and near infrared quantum cutting investigation of GdF3: Yb3þ, Ln3þ(Ln¼Ho, Tm, Er, Pr, Tb) nanoparticles, Phys. Chem. Chem. Phys. 15 (2013) 14295e14302. [19] J. Zhang, Y. Jin, C.Y. Li, Y.N. Shen, L. Han, Z.X. Hu, X.W. Di, Z.L. Liu, Creation of three-dimensionally ordered macroporous Au/CeO2 catalysts with controlled pore sizes and their enhanced catalytic performance for formaldehyde oxidation, Appl. Catal. B Environ. 91 (2009) 11e20. [20] F. Piret, M. Singh, C.G. Takoudis, B.L. Su, Optical properties in the UV range of a Ta2O5 inverse opal photonic crystal designed by MOCVD, Chem. Phys. Lett. 453 (2008) 87e91.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Influence of upconversion luminescence modification on near infrared luminescence and cooperative energy transfer in the YbPO4:Er3þ, Nb3þ/Er3þinverse opals excited at 980 or 808 nm Zhuangzhuang Chai, Zhengwen Yang*, Anjun Huang, Chengye Yu, Jianbei Qiu**, Zhiguo Song College of Materials Science and Engineering, Kunming University of Science and Technology, Kunming, 650093, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 May 2018 Received in revised form 1 July 2018 Accepted 8 July 2018 Available online 9 July 2018
The photoluminescence modification of rare earth ions base on the photonic band gap engineering was extensively reported. In this work, the effect of up-converting luminescence suppression of Er3þ on the near infrared luminescence and cooperative energy transfer from Er3þ to Yb3þ was investigated in the YbPO4 inverse opals single-doped with Er3þ and co-doped with Nd3þ and Er3þ. For the YbPO4:Er3þ inverse opals, when the photonic band gap is overlapped with the green or red up-converting luminescence of Er3þ, the green or red up-converting luminescence of Er3þ was suppressed in the YbPO4:Er3þ inverse opals upon the 980 nm excitation, respectively. It is significative that the enhancement of near infrared luminescence of Er3þ was observed, which is attributed to the electron redistribution in the excited energy levels caused by the upconversion luminescence suppression in the YbPO4:Er3þ inverse opals. For the YbPO4:Nd3þ,Er3þ inverse opals, the green upconversion and near infrared luminescence of Er3þ and the near infrared luminescence of Yb3þ were observed excited at 808 nm. The near infrared luminescence enhancement of Yb3þ was obtained due to the cooperative energy transfer enhancement from Er3þ to Yb3þ caused by the green upconversion luminescence suppression. The result is helpful to learn the relationship between upconversion and infrared luminescence in rare earth ions doped materials. © 2018 Published by Elsevier B.V.
Keywords: Inverse opals Upconversion luminescence Near infrared luminescence Cooperative energy transfer
1. Introduction Rare earth ions doped materials with near infrared (NIR) emission have great application prospects in the fields of the near infrared laser source, optical communication, biosensors and fluorescence immune analysis [1e4]. But the efficiency of near infrared emission of rare earth doped material is low owing to the presence of the competitive relationship between the NIR and upconversion (UC) luminescence, limiting its practical application. Therefore, the modification of UC luminescence may be required in order to obtain the high-efficient NIR luminescence. Photonic crystal is a type of ordered periodical dielectric materials, showing the photonic band gap property [5,6]. The motion of photons could be regulated by the photonic band gap [7], which exhibit the potential
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (Z. Yang), [email protected] (J. Qiu). https://doi.org/10.1016/j.jallcom.2018.07.092 0925-8388/© 2018 Published by Elsevier B.V.
applications in the fields of optical switch, optical filter and optical circuits, etc [8]. In addition, the photonic crystal can modify the spontaneous emission of active centers. The suppression or enhancements of spontaneous emission of active centers embedded in the photonic crystals were reported [9,10]. It is interesting that the photonic crystal can not only modulate the luminescence property of active centers, but also can cause the electron redistribution in the excited energy levels [11]. Thus the photonic crystals modulation provides a possible way to solve the problem of weak near infrared emission of rare earth ions by the modification of UC luminescence. Recently, the UC luminescence modification of rare-earth ions were extensively reported by the photonic crystals [12e14]. For instance, the UC emission suppression of rare earth ions in the region of the photonic band-gap and the enhancement at the photonic band edge were demonstrated in the rare earth ions doped inverse opals, respectively [12]. Additionally, the energy transfer enhancement from the Er3þ to Tm3þ induced by the photonic band gap was obtained, resulting in the enhancement of the
Z. Chai et al. / Journal of Alloys and Compounds 767 (2018) 16e22
short-wavelength UC luminescence [13]. The UC luminescence enhancement of rare earth doped nanoparticles was observed by the surface effect of photonic crystals [14]. Despite achieving many progresses of UC luminescence modification based on the photonic band gap, the influence of the UC luminescence modification on the NIR luminescence and cooperative energy transfer between the rare earth ions was rarely investigated by the photonic crystals. In this work, the YbPO4 inverse opals single-doped with Er3þ and codoped with Nd3þ and Er3þ were prepared by the sol-gel approach. The influence of UC luminescence suppression of Er3þ on the near infrared luminescence and the cooperative energy transfer from Er3þ to Yb3þ was investigated in the YbPO4 inverse opals singledoped with Er3þ and co-doped with Nd3þ and Er3þ, respectively. The enhancement of NIR luminescence property of Er3þ was realized due to the electron redistribution in excited state levels caused by modulating the UC luminescence in the YbPO4:Er3þ inverse opals. The near infrared luminescence enhancement of Yb3þ was observed due to the cooperative energy transfer enhancement from Er3þ to Yb3þ caused by the UC luminescence suppression in the YbPO4:Nd3þ, Er3þ inverse opals. 2. Experimental Three kinds of opal photonic crystals were self-assembled by using 300, 360 and 450 polystyrene (PS) microspheres, respectively, exhibiting the three-dimensional ordered structures. The Yb2O3, Er2O3 and P2O5 as the raw materials were used to prepare the YbPO4:Er3þ inverse opals. The Yb2O3 and Er2O3 were dissolved by the hot HNO3, respectively, and the excess HNO3 was evaporated to obtain ytterbium and erbium nitrification. The P2O5, ytterbium and erbium nitrification dissolved by the hydrous ethanol were mixed. After the stirring for 2 h, the homogeneous transparent YbPO4:Er3þ sol was prepared. The YbPO4:Er3 sol was filled into the voids of three kinds of opal photonic crystals, which was sintered at the 900 C in air. Then the YbPO4:Er3þ inverse opals were prepared. The preparation processes of YbPO4:Nd3þ, Er3þ inverse opals were similar with that of the YbPO4:Er3þ sol except that 1mol % Nd3þ was added into the homogeneous transparent YbPO4:Er3þ sol. The X-ray (XRD) diffractometer was used to characterize the crystallinity and phase purity of YbPO4 inverse opals single-doped with Er3þ and co-doped with Nd3þ and Er3þ. The micro-structures
17
of YbPO4 inverse opals single-doped with Er3þ and co-doped with Nd3þ and Er3þ were characterized by the scanning electron microscope (SEM). The NIR and UC luminescence spectra of YbPO4:Er3þ inverse opals were measured by the FLSP-980 spectrophotometer under the excitation of 980 nm and the NIR and UC luminescence spectra of YbPO4:Nd3þ, Er3þ inverse opals were measured excited at the 808 nm. The excitation power of 808 and 980 nm was 1.7 W. The photonic band gap property of YbPO4 inverse opal was characterized by the absorption spectra (Hitachi U4100 spectrophotometer). The decay curves of UCL were characterized by the FLSP-980 spectrophotometer. 3. Results and discussion 3.1. Influence of upconversion luminescence modification on near infrared luminescence in the YbPO4:Er3þ inverse opals excited at the 980 nm The YbPO4:Er3þ inverse opals prepared by the 300, 360 and 450 nm opals were designated as the IPC-I, IPC-II and IPC-III, respectively. Fig. 1 (a) presented the XRD patterns of YbPO4:Er3þ inverse opals prepared by the 300, 360 and 460 nm opal templates and the standard PDF card (NO.43-0530). The XRD diffraction peaks of YbPO4 inverse opals without and with the doping of Er3þ can be indexed by the standard PDF card, suggesting the preparation of monoclinic YbPO4:Er3þ inverse opals. The Debye-Scherer equation was applied to calculate the grain size of YbPO4 in the IPC-I, IPC-II and IPC-III, which were about 76.6, 72.2 and 75.3 nm, respectively. Fig. 1 (b)-(d) presented the SEM images of opals self-assembled by the 300, 360 and 450 nm PS microspheres, respectively, showing the ordered structures with face centered cubic close packing. The SEM images of the IPC-I, IPC-II and IPC-III were exhibited in the Fig. 1 (e)-(g). The YbPO4:Er3þ inverse opals replicated the reverse structure of opal templates, having a long range order in threedimensional space. The center to center distance between the two near air-spheres of IPC-I, IPC-II and IPC-III was obtained according to the SEM images exhibited in Fig. 1, which was about 227, 280, and 336 nm, respectively. In comparison with the size of raw PS microspheres, the shrinkage of about 24.3%, 22.2% and 26.3% was observed for the IPC-I, IPC-II and IPC-III after the calcination, respectively.
Fig. 1. The XRD patterns (a) of IPC-I, IPC-II and IPC-III; the SEM images of opals self-assembled by the 300 (b), 360 (c) and 450 nm (d) PS microspheres; the SEM images of IPC-I (e), IPC-II (f) and IPC-III (g).
18
Z. Chai et al. / Journal of Alloys and Compounds 767 (2018) 16e22
Fig. 2 exhibited the UVevisible absorption spectra of IPC-I, IPC-II and IPC-III. The obvious absorption peak at the 420, 540 and 645 nm was observed in the IPC-I, IPC-II and IPC-III, respectively, which was caused by the Bragg diffraction of ordered structure of inverse opals. The center to center distance (D) between the two near air-spheres for the IPC-I, IPC-II and IPC-III was calculated by using the refractive index (neff) and photonic band gap position (l) of YbPO4 inverse opal and based on the Bragg equation and Snell's law [14]:
Fig. 2. The absorption spectra of IPC-I, IPC-II and IPC-III
r ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi n2eff sin2 q
(1)
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi n2 f þ n2air ð1 f Þ
(2)
l ¼ 1:633D
neff ¼
where nair, n and q denotes as the refractive indexes of air (1), YbPO4 (1.68 obtained at about 500 nm) [15], and the angle between the normal line of inverse opal and the incidence light, respectively. For the inverse opal with close packing face centered cubic structure, the volume fraction of YbPO4 is about 26%. The center to center distance (D) of two near air-spheres for the IPC-I, IPC-II and IPC-III was calculated to be about the 231, 278 and 333 nm, respectively, which is coincident with these obtained by the SEM images. Fig. 3 (a) and (b) show the UC luminescence spectra of IPC-I, IPCII and IPC-III upon the 980 nm excitation. The 524, 548, and 660 nm UC luminescence was observed, corresponding to the 2H11/2 / 4I15/ 4 4 4 4 3þ 2, S3/2 / I15/2 and F9/2 / I15/2 of Er , respectively [16]. It is noted that the photonic band gap of the IPC-II and IPC-III was located at about 540 and 645 nm, respectively, which is overlapped with the 524/548 nm green and 660 nm red UC luminescence. The 524/548 and 660 nm UC luminescence is suppressed in the IPC-II and IPC-III, respectively, in comparison with the IPC-I, which is a typical modulation phenomenon of UC luminescence caused by the photonic band gap [11]. The NIR pump power dependence of UC luminescence intensity can be used to characterize the UC mechanism. It is well-known that the UC luminescence intensity Iup is proportional to the NIR excitation power (P), which can be
Fig. 3. The UC luminescence of the IPC-I/IPC-II (a) and IPC-II/IPC-III (b) upon the 980 nm excitation; the UC luminescence intensity of IPC-I as a function of excitation power (c); the UC luminescence mechanism of YbPO4:Er3þ inverse opals (d).
Z. Chai et al. / Journal of Alloys and Compounds 767 (2018) 16e22
expressed as IupfPn. In the IupfPn equation, the n is the photon numbers absorbed by the Er3þ in the UC luminescence process. The UC luminescence intensity of the IPC-I was measured as a function of the excitation power, as shown in the Fig. 3 (c), which exhibited that the red and green UC luminescence was attributed to the two photons processes. Fig. 4 (b) shows the UC luminescence mechanism of YbPO4:Er3þ inverse opals under the excitation of 980 nm. The energy transfer (ET) from Yb3þ to Er3þ ions excited the Er3þ ions, resulting in the population of 4I11/2 state. The electrons at the 4 I11/2 state jumped to the 4F7/2 level by the further ET excitation. The electrons at the 4F7/2 state relaxed non-radiatively to the near 4S3/2 and 2H11/2 levels. The 2H11/2/4S3/2 / 4I15/2 radiative transitions lead to the generation of the 524/548 nm UC luminescence. For the 660 nm UC luminescence, the non-radiative relaxation of the 4I11/2 level populated the 4I13/2 level. The electrons at the 4I13/2 state jumped to the 4F9/2 levels by the further ET excitation. In addition, the electrons at the 2H11/2/4S3/2 states can relax non-radiatively to the 4F9/2 level. Thus the 4F9/2 / 4I15/2 transition generates the 660 nm UC luminescence. The NIR luminescence spectra of YbPO4:Er3þ inverse opals were measured upon the 980 nm excitation, as shown in Fig. 4 (a) and (b). The NIR luminescence peak centered at 1550 nm ranging from 1450 to 1600 nm was observed in the IPC-I, IPC-II and IPC-III, which
Fig. 4. The NIR luminescence spectra of IPC-I/IPC-II (a) and IPC-I/IPC-III (b) upon the 980 nm excitation.
19
is corresponding to the transition from 4I13/2 to 4I15/2 of Er3þ. As shown in Fig. 3(d), the 4I13/2 / 4I15/2 radiative transition results in the generation of the NIR luminescence centered at 1550 nm ranging from 1450 to 1600 nm. It is interesting that the NIR luminescence in the IPC-II and IPC-III was enhanced in contrast to the IPC-I because of the UC luminescence modification caused by the photonic band gap. As shown in Fig. 3 (d), the electrons located at the 4F9/2, 2H11/2 and 4S3/2 excitation state can loss their energy by the two paths: the non-radiative relaxation form 4F9/2, 2H11/2 and 4 S3/2 levels to the 4I13/2 level or the UC luminescence transition from 4 F9/2, 2H11/2 and 4S3/2 to 4I15/2 ground state. The UC luminescence from the 4S3/2/2H11/2 and 4F9/2 to 4I15/2 ground state compete with the non-radiative relaxation form 4F9/2, 2H11/2 and 4S3/2 levels to the 4 I13/2 level. The inhibition of UC luminescence from the 4F9/2 and 4 S3/2/2H11/2 to 4I15/2 ground state in the YbPO4:Er3þ inverse opals can cause the enhancement of non-radiative relaxation from the 4 F9/2 and 4S3/2/2H11/2 to 4I13/2 state. As a result, the enhancement of NIR luminescence from the 4I13/2 / 4I15/2 radiative transition in the IPC-II and IPC-III were observed in contrast to the IPC-I. 3.2. Influence of upconversion luminescence modification on cooperative energy transfer in the YbPO4:Nb3þ/Er3þinverse opals excited at the 808 nm Two kinds of YbPO4:Nd3þ,Er3þ inverse opals were prepared by filling the YbPO4:Nd3þ, Er3þ sol into the opal templates selfassembled by the 300 and 360 nm polystyrene (PS) microspheres. The YbPO4:Nd3þ, Er3þ inverse opals prepared by the 300 and 360 nm opal templates were designated as the IPC-IV and IPC-V, respectively. Fig. 5 presented the XRD patterns and SEM images of the IPC-IV and IPC-V. The YbPO4:Nd3þ, Er3þ inverse opals are the monoclinic phase regarding of the size of PS microspheres, exhibiting an order structure. The doping of Nd3þ has no influence on the phase and order structure of YbPO4:Er3þ inverse opals. The grain size of YbPO4 for the IPC-IV and IPC-V calculated by the Scherer equation based on the XRD patterns was about the 77.1 and 74.8 nm, respectively. According to the SEM images shown in Fig. 5, the center to center distance between the near two air-spheres for the IPC-IV and IPC-V was about 230 and 276 nm, respectively. Compared with raw size of PS microspheres, the shrinkage of about 23.6 and 23.1% was obtained for the IPC-IV and IPC-V after the hightemperature calcination, respectively. Fig. 6 (a) showed the absorption spectra of IPC-IV and IPC-V. The photonic band gap caused by the Bragg diffraction of ordered structure for the IPC-IV and IPC-V was located at the 420 and 543 nm, respectively. The center to center distance (D) between the two near air-spheres of IPC-IV and IPC-V was calculated by the Bragg equation and Snell's law, which was about the 228 and 280 nm, respectively. The calculated results are coincident with these obtained by the SEM images. Fig. 6 (b) shows the UC luminescence spectra of IPC-IV and IPC-V upon the 808 nm excitations, exhibiting the 524 and 548 nm UC luminescence, which is corresponding to the 2H11/2 / 4I15/2 and 4S3/2 / 4I15/2 of Er3þ, respectively. The suppression of 524 and 548 nm UC luminescence is observed in the IPC-V in contrast to the IPC-IV due to the typical photonic band gap effect [17]. The 808 nm NIR pump power dependence of UC luminescence intensity for the IPC-IV was shown in the Fig. 6 (c), which exhibited that the green UC luminescence was from the two photons processes. The UC luminescence spectra of the IPC-I～III inverse opals without the Nd3þ doping were measured upon the 808 nm excitations, as shown in Fig. S1 of supporting information. No green UC luminescence of Er3þ was observed for the IPC-I～III inverse opals without the Nd3þ doping, which suggested that the green UC luminescence of Er3þ of IPC-IV and IPC-V is related to the Nd3þ doping upon the 808 nm
20
Z. Chai et al. / Journal of Alloys and Compounds 767 (2018) 16e22
Fig. 5. The XRD patterns (a) of the IPC-IV and IPC-V; the SEM images of IPC-IV(b) and IPC-V(c).
Fig. 6. The absorption spectra of IPC-IV and IPC-V(a); the UC luminescence spectra of the IPC-IV and IPC-V (b) upon the 808 nm excitation; the UC luminescence intensity of IPC-IV as a function of excitation power (c); the UC luminescence mechanism of YbPO4:Nd3þ, Er3þ inverse opals (d).
excitations. The UC luminescence mechanism of YbPO4: Nd3þ, Er3þ inverse opals was provided under the excitation of 808 nm, as shown Fig. 6 (d). The Nd3þ was excited to the 4F5/2 state from the ground state under the excitation of 808 nm. The energy transfer (ET) from Nd3þ to Yb3þ ions excited the Er3þ ions, populating the 2 F5/2 state of Yb3þ ions. The two-steps energy transfer (ET) from Yb3þ to Er3þ populated the 2H11/2/4S3/2 levels of Er3þ. The 2H11/2/4S3/ 4 2 / I15/2 radiative transitions produce the 524/548 nm UC
luminescence. Fig. 7 exhibited the NIR luminescence spectra of YbPO4: Nd3þ, 3þ Er inverse opals upon the 808 nm excitations. The NIR luminescence ranging from 1450 to 1600 nm in the IPC-IV and IPC-V is from the transition from 4I13/2 to 4I15/2 of Er3þ, as shown in Fig. 3 (d). The NIR luminescence ranging from 925 to 1050 nm was attributed to the 2F5/2 / 2F7/2 radiative transition of Yb3þ. In order to obtain the NIR luminescence mechanism of Yb3þ, the NIR spectrum of IPC-I
Z. Chai et al. / Journal of Alloys and Compounds 767 (2018) 16e22
Fig. 7. The near-infrared luminescence spectra (a, b) of the IPC-I, IPC-IV and IPC-V upon the 808 nm excitation, the decay curves of 548 nm UC luminescence (c) of IPCIV and IPC-V upon the 808 nm excitation.
inverse opal without the Nd3þ doping was measured upon the 808 nm excitations, as shown in Fig. 7 (a). It is noted that no NIR luminescence of Yb3þ was observed for the IPC-I inverse opal without the Nd3þ doping, which suggested that the NIR luminescence of Yb3þ is attributed to the energy transfer from the Nd3þ to Yb3þ. The energy transfer (ET) from Nd3þ to Yb3þ ions excited the Er3þ ions, populating the 2F5/2 state of Yb3þ ions. The radiative transition from 2F5/2 state to ground state results in the NIR luminescence of Yb3þ. In addition, it is reported that the cooperative energy transfer from the Er3þ to 2Yb3þ can cause the NIR luminescence of Yb3þ [18], and the cooperative energy transfer was expressed as the 4S3/2/2H11/2 (Er3þ)/22F5/2 (Yb3þ), as shown in
21
Fig. 6 (d). The NIR luminescence ranging from 1450 to 1600 nm in the IPCV was enhanced upon the 808 nm excitation in contrast to the IPCIV because of the green UC luminescence suppression caused by the photonic band gap. The enhancement mechanism of NIR luminescence ranging from 1450 to 1600 nm of YbPO4: Nd3þ, Er3þ inverse opals upon the 808 nm excitation is similar with that of YbPO4: Er3þ inverse opals upon the 980 nm excitation. The inhibition of green UC luminescence from 4S3/2/2H11/2 to 4I15/2 ground state in the YbPO4: Nd3þ, Er3þ inverse opals can cause the enhancement of non-radiative relaxation from the 4S3/2/2H11/2 to 4 I13/2 state, result in the NIR luminescence enhancement for the IPC-V. It is interesting that the NIR luminescence ranging from 925 to 1050 nm of Yb3þ was enhanced in the IPC-V in contrast to the IPCIV. The NIR luminescence of Yb3þ are attributed to the two mechanisms: the energy transfer from Nd3þ to Yb3þ ions and the cooperative energy transfer from the Er3þ to 2Yb3þ. The energy transfer from Nd3þ to Yb3þ ions was not influence by photonic band gap because the absorption and luminescence of Nd3þ and Yb3þ ions is apart from the photonic band gap [19]. The enhancement of NIR luminescence of Yb3þ is attributed to the enhanced cooperative energy transfer from the Er3þ to 2Yb3þ. The 2H11/2 and 4S3/2 excitation state can loss their energy by the two paths: the cooperative energy transfer from the Er3þ at 4S3/2/2H11/2 excited state to 2Yb3þ or the UC luminescence transitions from 2H11/2 and 4S3/2 to 4I15/2 ground state. The UC luminescence from the 4S3/2/2H11/2 to 4I15/2 ground state compete with the cooperative energy transfer from the Er3þ at 4S3/2/2H11/2 excited state to 2Yb3þ. The inhibition of UC luminescence from the 4S3/2/2H11/2 to 4I15/2 ground state in the YbPO4:Nd3þ,Er3þ inverse opals can cause the enhancement of the cooperative energy transfer from the Er3þ to 2Yb3þ. As a result, the NIR luminescence enhancement of Yb3þ for the IPC-V was observed in contrast to the IPC-IV. In order to demonstrate the enhancement of cooperative energy transfer from the Er3þ to 2Yb3þ, the decay curves of 548 nm UC luminescence of IPC-IV and IPC-V inverse opals was measured upon the 808 nm excitation, as shown in Fig. 7 (c). The UC luminescence decay curves of rare earth ions doped phosphors can be described by single or double exponential equation due to the occupation of various sites of RE ions in the host []. In present work, the photonic band gap has an influence on the decay lifetimes of Er3þ ions, which result in that the decay curves were not fitted by the single exponential equation. Therefore, the decay curves were fitted by using a double exponential equation. It can be seen that the in the UC decay lifetime of 548 nm UC luminescence in the IPC-V inverse opal was decreased in contrast to that of the IPC-IV inverse opal. It is well-known that the photonic band gap can cause the increasing or no changing of UC decay lifetime when the photonic band gap is overlapped with the luminescence peak [20]. In the present work, the UC decay lifetime of 548 nm UC luminescence in the IPC-V inverse opal was decreased in contrast to that of the IPC-IV inverse opal although the photonic band gap of IPC-V inverse opal is overlapped with the 548 nm UC luminescence, which is caused by the enhancement of the cooperative energy transfer from the Er3þ to 2Yb3þ. 4. Conclusions The YbPO4 inverse opals single-doped with Er3þ and co-doped with Nd3þ and Er3þ were prepared by the sol-gel approach. The influence of upconversion luminescence modification of Er3þ on the near infrared luminescence was investigated in the YbPO4:Er3þ inverse opals. The green, red upconversion luminescence and near infrared luminescence were observed in the YbPO4:Er3þ inverse opals upon the 980 nm excitation. The near infrared luminescence
22
Z. Chai et al. / Journal of Alloys and Compounds 767 (2018) 16e22
of Er3þ was enhanced when the photonic band gap is overlapped with the green or red up-converting luminescence of Er3þ, which is attributed to the electron redistribution in the excited energy levels caused by the upconversion luminescence suppression in the YbPO4:Er3þ inverse opals. The influence of upconversion luminescence modification of Er3þ on the cooperative energy transfer from Er3þ to 2Yb3þ was observed in the YbPO4:Nd3þ, Er3þ inverse opals upon the 808 nm excitations. The cooperative energy transfer enhancement from Er3þ to 2Yb3þ was enhanced due to the upconversion luminescence suppression of Er3þcaused by the photonic band gap effect, resulting in the enhancement of near infrared luminescence of Yb3þ. Acknowledgments This work was supported by the National Natural Science Foundation of China (51762029), and the Applied basic research key program of Yunnan Province. Appendix A. Supplementary data Supplementary data related to this article can be found at https://doi.org/10.1016/j.jallcom.2018.07.092. References [1] D.K. Chatteriee, A.J. Rufalhah, Y. Zhang, Upconversion fluorescence imaging of cells and small animals using lanthanide doped nanocrystals, Biomaterials 29 (2008) 937e943. [2] S. Heer, K. Kompe, H.U. Gudel, M. Haase, Highly efficient multicolour upconversion emission in transparent colloids of lanthanide-doped NaYF4 nanocrystals, Adv. Mater. 16 (2004) 2102e2105. [3] C. Klein, M.K. Nazeeruddin, P. Liska, D. Di Censo, N. Hirata, E. Palomares, J.R. Durrant, M. Gratzel, Engineering of a novel ruthenium sensitizer and its application in dye-sensitized solar cells for conversion of sunlight into electricity, Inorg. Chem. 44 (2005) 178e180. [4] H. Lin, D.Q. Chen, Y.L. Yu, Z.F. Shan, P. Huang, Y.S. Wang, J.L. Yuan, Nd3þsensitized upconversion white light emission of Tm3þ/Ho3þTm3þ/Ho3þbridged by Yb3þ in b-YF3 nanocrystals embedded transparent glass ceramics, J. Appl. Phys. 107 (2010), 103511. [5] S. Xu, W. Xu, Y.F. Wang, S. Zhang, Y.S. Zhu, L. Tao, L. Xia, P.W. Zhou, H.W. Song, NaYF4:Yb,Tm nanocrystals and TiO2 inverse opal composite films: a novel device for upconversion enhancement and solid-based sensing of avidin,
Nanoscale 6 (2014) 5859e5870. [6] Y.D. Yang, P.W. Zhou, W. Xu, S. Xu, Y.D. Jiang, X. Chen, H.W. Song, NaYF4: Yb3þ,Tm3þ inverse opal photonic crystals and NaYF4:Yb3þ,Tm3þ/TiO2 composites: synthesis, highly improved upconversion properties and NIR photoelectric response, J. Mater. Chem. C 4 (2016) 659e662. [7] M.O.A. Erola, A. Philip, T. Ahmed, S. Suvanto, T.T. Pakkanen, Fabrication of Auand Ag-SiO2 inverse opals having both localized surface plasmon resonance and Bragg diffraction, J. Solid State Chem. 230 (2015) 209e217. [8] B.T. Holland, C.F. Blanford, T. Do, A. Stein, Synthesis of highly ordered, threedimensional, macroporous structures of amorphous or crystalline inorganic oxides, phosphates, and hybrid composites, Chem. Mater. 11 (1999) 795e805. [9] S.F. Lai, Z.W. Yang, J. Li, B. Shao, J.Z. Yang, Y.D. Wang, J.B. Qiu, Z.G. Song, Photoluminescence enhancement of Eu3þ ions by Ag species in SiO2 threedimensionally ordered macroporous materials, J. Mater. Chem. C 3 (2015) 7699e7708. [10] H.B. Sun, S. Matsuo, H. Misawa, Three-dimensional photonic crystal structures achieved with two-photon-absorption photopolymerization of resin, Appl. Phys. Lett. 74 (1999) 786e788. [11] Z.D. Liu, Z.W. Yang, L. Sun, B. Li, J. Zhou, Energy transfer enhancement in Eu3þ, Tb3þ-Doped SiO2 inverse opal photonic crystals, J. Am. Ceram. Soc. 94 (2011) 2731e2734. [12] Z.Z. Chai, Z.W. Yang, A.J. Huang, C.Y. Yu, J.B. Qiu, Z.G. Song, Preparation and upconversion luminescence modification of YbPO4:Er3þ inverse opal heterostructure, J. Rare Earths 35 (2017) 1180e1185. [13] V.A.G. Rivera, M. El-Amraoui, Y. Ledemi, Y. Messaddeq, E. Marega, Expanding broadband emission in the near-IR via energy transfer between Er3þ-Tm3þ codoped tellurite-glasses, J. Lumin. 145 (2014) 787e792. [14] J.Y. Liao, Z.W. Yang, S.F. Lai, B. Shao, J. Li, J.B. Qiu, Z.G. Song, Y. Yang, Upconversion emission enhancement of NaYF4:Yb,Er nanoparticles by coupling silver nanoparticle plasmons and photonic crystal effects, J. Phys. Chem. C 118 (2014) 17992e17999. [15] H. Lin, D.Q. Chen, M.T. Niu, Y.L. Yu, P. Huang, Y.S. Wang, Synthesis and upconversion emission of rare earth-doped olive-like YF3 micro-particles, Mater. Res. Bull. 45 (2010) 52e55. [16] Z. Khadraoui, K. Horchani-Naifer, M. Ferhi, M. ferid, Synthesis, characterization and DFT calculation of electronic and optical properties of YbPO4, Chem. Phys. 457 (2015) 37e42. [17] J.Q. Wang, C.W. Zhou, L. Su, X.Y. Ji, X.B. Chen, M. Zhang, Preparation of inverse opal cerium dioxide for optical properties research, Mater. Lett. 158 (2015) 123e127. [18] L.N. Guo, Y.H. Wang, W. Zeng, L. Zhao, L.L. Han, Band structure and near infrared quantum cutting investigation of GdF3: Yb3þ, Ln3þ(Ln¼Ho, Tm, Er, Pr, Tb) nanoparticles, Phys. Chem. Chem. Phys. 15 (2013) 14295e14302. [19] J. Zhang, Y. Jin, C.Y. Li, Y.N. Shen, L. Han, Z.X. Hu, X.W. Di, Z.L. Liu, Creation of three-dimensionally ordered macroporous Au/CeO2 catalysts with controlled pore sizes and their enhanced catalytic performance for formaldehyde oxidation, Appl. Catal. B Environ. 91 (2009) 11e20. [20] F. Piret, M. Singh, C.G. Takoudis, B.L. Su, Optical properties in the UV range of a Ta2O5 inverse opal photonic crystal designed by MOCVD, Chem. Phys. Lett. 453 (2008) 87e91.