Visible to infrared low temperature luminescence of Er3+, Nd3+ and Sm3+ in CaSnO3 phosphors

Author’s Accepted Manuscript Visible to infrared low temperature luminescence of Er3+, Nd3+ and Sm3+ in CaSnO3 phosphors V. Orsi Gordo, Y. Tuncer Arslanli, A. Canimoglu, M. Ayvacikli, Y. Galvão Gobato, M. Henini, N. Can www.elsevier.com/locate/apradiso

PII: DOI: Reference:

S0969-8043(15)00063-9 http://dx.doi.org/10.1016/j.apradiso.2015.02.019 ARI6919

To appear in: Applied Radiation and Isotopes Received date: 6 February 2015 Revised date: 20 February 2015 Accepted date: 20 February 2015 Cite this article as: V. Orsi Gordo, Y. Tuncer Arslanli, A. Canimoglu, M. Ayvacikli, Y. Galvão Gobato, M. Henini and N. Can, Visible to infrared low temperature luminescence of Er3+, Nd3+ and Sm3+ in CaSnO3 phosphors, Applied Radiation and Isotopes, http://dx.doi.org/10.1016/j.apradiso.2015.02.019 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Visible to infrared low temperature luminescence of Er3+, Nd3+ and Sm3+ in CaSnO3 phosphors V. Orsi Gordoa,d, Y. Tuncer Arslanlib, A. Canimogluc, M. Ayvaciklib,Y.Galvão Gobatod, M. Heninia, N. Canb,e a

School of Physics and Astronomy, Nottingham Nanotechnology and Nanoscience Center, University of Nottingham, Nottingham NG7 2RD, UK b Celal Bayar University, Faculty of Arts and Sciences, Department of Physics, Muradiye-Manisa, Turkey c Niğde University, Faculty of Arts and Sciences, Physics Department, Nigde, Turkey d Departamento de Física, UFSCAR, 13565-905, São Carlos, SP, Brazil e Physics Department, Jazan University, P.O. Box 114, 45142 Jazan, Kingdom of Saudi Arabia  Email address: [email protected]

Abstract Novel stannate phosphor, orthorhombic CaSnO3 phosphors doped with Er3+, Nd3+ and Sm3+ have been synthesized by conventional solid-state method under N2 + H2 gas flow. Visible and nearinfrared photoluminescence (PL) properties were investigated as function of laser power and temperature. It was observed that all dopant ions are well incorporated in CaSnO3 and are responsible for the optical emission in the temperature range of 10-300K. PL peaks at 490, 546, 656, 696, 894, 1065, and 1344 nm were observed for the CaSnO3:Nd3+ phosphor and associated to f-f transition of Nd3+ ion. Emissions at 564, 600-607, 646-656 and 714 nm were detected for the CaSnO3: Sm3+. The strongest one, observed at 600 nm, was associated to 4G5/2 → 6H7/2 of Sm3. Emission lines at 528, 548, 662 at 852 nm were also seen for CaSnO3:Er3+ and correspond to Er3+ intra-4fn shell transitions. In addition, at low temperatures, a stark splitting of the 4f electron energy levels of the Er3+ ions were observed in infrared region (1520-1558 nm) and assigned to the transition between the 4I13/2 state and the 4I15/2 state. Finally, our results show that the rare earth doped CaSnO3 have remarkable potential for applications as optical materials since it exhibits efficient and sharp emissions due to rare earth ions.

Keywords: CaSnO3; Rare earth; low temperature; photoluminescence

1.

Introduction Phosphor materials have been extensively studied for several applications such as display

devices including plasma display panels, field emission display, solid state lighting sources and other novel technologies (Kotan et al., 2013; Zhu and Yang, 2013; Kamtekar et al., 2010). Undoubtedly, rare-earth doped phosphors emitting at different wavelengths in the electromagnetic spectrum also play a critical role in solid state lighting and display fields as they exhibit abundant emission colours attributed to their 4f–4f or 5d–4f transitions (Sivakumar and Varadaraju 2008; Sun et al., 2012). Oxide phosphors are more desirable than traditional sulphide or halide luminescence phosphors for applications due to their resistance to moisture and high brightness. In addition phosphors doped with rare earth ions can be easily produced in large quantities via solid-state synthesis. Moreover, many luminescence properties of phosphors strongly depend on the particle size, chemical composition and crystal structure of the host material. It is therefore important to study the local structure using techniques such as SEM and XRD. It has been reported that SnO44− anions are expected to be optically inert and could be very promising candidates for host materials (Lei et al., 2007). Orthorhombic perovskite structure of CaSnO3, is made up of octahedral SnO6 whose vertices are connected to each other by sharing edges. Furthermore, the structure of Ca2SnO4, which consists of SnO6 octahedra that are linked by edges and seven oxygen ions surrounding Ca2+, exhibits arrangement with a low symmetry (Yang et al., 2005). Long afterglow phosphors (LAPs) possess specific properties such as storing light energy, glowing, and fading out slowly in the dark (Palilla et al., 1968). The green-blue, yellowgreen, and blue LAPs with high brightness, environmental acceptabal and long life are widely available in the commercial market (Matsuzawa et al., 1996; Liu et al., 2005; Teng et al., 2008).

However, afterglow intensity and/or long duration of orange to red LAP is far away from the target that might be expected, and commercial applications are still limited (Lei et al., 2010). Although considerable efforts have gone into research of orange to red LAP, the progress is still very slow (Huang et al., 2009). Important active ions are rare earth ions like Eu, Er, Nd, Sm, Tb and these ions have been widely used in the form of the trivalent ion in luminescent materials for the last several decades. The lanthanides are characterized by extremely localized 4f shell that is shielded from external fields by the outer 5s2 and 5p6 electrons. The transitions, therefore, will yield sharp lines in the optical spectra. More recently, white light emitting diodes (LED) that have been widely used with trivalent rare earth ions are attractive devices because of their particular luminescence emissions in the 380 – 760 nm range which corresponds to the important visible region of the electromagnetic spectrum. It is well known that Nd3+ doped materials have attracted considerable attention due to potential applications as high efficient light sources for powerful solid-state lasers. Sm3+ ion from the Ln3+ family is also an important activator for the luminescence material which emits bright orange/red light. Er3+-doped host materials have been studied as light sources as they display green emissions (Yan et al., 2011). Er3+ also shows particular luminescence property in the long wavelength which can be used in the laser field (Ajithkumar et al., 2013). During last decade, more attention has been paid to rare earth activated alkaline earth stannates (MSnO3, M2SnO4 where M = Ca, Sr and Ba) as host matrix for new phosphors due to their stable crystalline structure and high chemical and physical stability (Kotan et al., 2013; Liang et al., 2013; Lei et al., 2007; Lei, Li and Zhang 2007; Lei et al., 2011; Yang et al., 2005; Pang et al., 2011; Yamane et al., 2008; Stanulis et al., 2014; Chen et al., 2010; Xu et al., 2011).

In this work, we have investigated optical properties of CaSnO3:Sm3+, Nd3+, Er3+ phosphors synthesized by solid state reaction method. We have performed PL measurements as function of temperature (10-300K) and laser power for Sm3+, Nd3+ and Er3+ doped CaSnO3 samples. Several strong sharp lines associated to Sm3+, Nd3+ and Er3+ ions were observed. The nature and limitation of the interaction between the host material and the activator ions are also discussed. Our PL results show that the rare earth doped CaSnO3 have remarkable potential for applications as optical materials since it exhibits efficient and sharp emission due to rare earth ions.

2.

Materials and experimental techniques Our powder samples of CaSnO3:Er3+, Nd3+, Sm3+ were synthesised through solid-state

reaction. CaCO3 (Sigma Aldrich 99.99% pure), SnO2, Nd2O3, Er2O3 and SmO2 (Sigma-Aldrich >99.9% pure) were used for the preparation of rare earth doped CaSnO3 phosphors. The stoichiometric amount of starting materials was thoroughly mixed in an agate mortar. The mixture was put into alumina crucibles, and then calcined at 1200 C for 2 hours under the flow of 5% H2 + 95% N2. After being calcined, the powders were allowed to cool down in a reducing atmosphere to room temperature in the furnace, and then final products were collected and ground into fine powder. As the doping concentration exceeds the critical concentration (1 mol%) emission intensities decrease dramatically therefore the contributions of all rare elements in the batch are chosen as 1 mol %. An X-ray diffractometer (XRD, Philips X'Pert Pro), which uses Cu K line ( = 1.5418 Å) at a scanning rate of 0.5 /min in the range from 5 to 70 was employed for the identification of the crystallographic phases.

PL spectra of the synthesized phosphor were recorded by using a Horiba iHR 550 spectrometer with dual color Si/InGaAs Peltier cooled detector. A 474 nm blue diode laser was used as excitation source. The samples were placed in a Janis closed cycle helium cryostat and the temperature was changed from 300 to 10K.

3.

Results and discussions

3.1

XRD analysis

X-ray powder diffraction (XRD) was measured to investigate the phase purity and crystal structure of the products. Typical XRD patterns of synthesized samples of pure CaSnO3 and CaSnO3 doped with Er, Nd, and Sm are shown in Figure 1. XRD patterns clearly indicate that the products have an orthorhombic crystallographic structure whose space group is Pbnm. All the diffraction peaks match well with the standard data for CaSnO3 (JCPDS no. 77-1797). One must also note that there is no discernible change as shown in Figure 1. Therefore the introduction of small amount of Er3+, Nd3+, and Sm3+ ions do not give rise to a detectable influence on the crystal structure.

3.2

Luminescence We have investigated the photoluminescence spectra of pure CaSnO3 (reference sample) and

Er, Nd, and Sm doped CaSnO3 as function of temperature and laser power. Nevertheless, it is rarely mentioned in the literature that the same high sensitivity to ppm levels of impurities will equally mean that this type of experiment is sensitive to the purity of the starting materials, and the processing procedures. We typically use 99.99% purity materials, but the trace impurities may still influence our data (and of course the results on samples reported by

other groups). For a number of lanthanides multiple oxidation states are possible, the final oxidation state depending on the choice of raw materials, the method of synthesis and the type of matrix they are incorporated in. All of the lanthanides used here exhibit stable structure in the trivalent state.

3.2.1 Undoped CaSnO3 Figures 2 a and b display PL spectra recorded from pure CaSnO3 at different laser power densities varying from 2mW to 30 mW at 10 K and 300 K, respectively. The figures clearly indicate that the PL intensity increases with laser power density as expected. Note also that Figure 2 exhibits no appreciable shift in the PL peak wavelength with increasing power density. Figure 3 indicates an overall isometric view of the photoluminescence spectra of pure CaSnO3 during the cooling. The color coded map (Figure 3b) clearly shows that the PL presents two different emission bands. We have observed a wide broad band centered at 780 nm at 300 K corresponding to an intrinsic defect center or centers in CaSnO3 as stated in our earlier work (Karabulut et al., 2014). However an unusual result was obtained for low temperatures. Particularly, the broad band observed at 780 nm has been completely suppressed. Another red signal (700 nm) was observed around 170 K which becomes more intense as the temperature is decreased. In other words, the 780 nm broad emission shows an unusual behaviour, since it decreases with increasing temperature and is undetectable beyond 170 K. This dramatic feature is clearly observed in the isometric or contour plot of undoped CaSnO3. At low temperature PL measurements, one would expect to see significantly better resolution and more intense emissions since the phonon emissions are reduced. In our case, the broad band located at 780 nm is observed only at high temperatures and during the cooling it decreases sharply at about

170 K. Surprisingly, as can be seen from Figure 3 the intensity of the emission line at 700 nm begins to increase significantly as the 780 nm emission decays. These results may be interpreted in terms of the process of energy transfer between host lattice and some other unintentionally incorporated ions. On the other hand at about room temperature, transfer of energy is more preferable to the 780 nm emission whilst it is made to the lower wavelength (700 nm) (higher energy) during the cooling. However, neither the rare earth ions used in this study nor other ones have a known energy level in this region. It is difficult to identify this luminescence centre with any known imperfections. Therefore this anomalous behaviour is not well understood and is still under investigation. The photoluminescence spectrum was also recorded in the infrared region for undoped CaSnO3 phosphor by using InGaAs detector. However no emission line was detected for infrared region.

3.2.2 Er3+ emission spectra PL of Er3+ doped CaSnO3 sample was investigated in the temperature range of 10-300 K by using a 474 nm diode laser at 20 mW. The introduction of Er ions gives rise to several sharp bands in the visible (VIS)- near infrared (NIR) spectral region ( Figures 4 and 5). Some emission lines detected in the VIS/NIR spectral range correspond to well-documented rare earth 4f transitions. Intensities of the main PL emissions are mostly similar at 10 K and room temperature, but relative changes of line intensities are observed. As it is seen in Figure 4a, green emissions at 545 and 547 nm (separated into two Stark levels) along with a shoulder centred at 528 nm are clearly observed. This band has been attributed to 4S3/2→4I15/2 and 2H11/2→4I15/2 transitions of Er3+ as illustrated in the possible energy transitions for Er3+ shown in Figure 6. These transitions are in good agreement with those observed in the literature (Singh et al.,2009).

The observed red and near IR emissions located at 662 nm and 852 nm are associated to 4

F9/2→4I15/2 and 4S3/2→4I13/2 transitions. The contour map illustrated in Figure 4a shows that the

emission bands do not change significantly with temperature. Figure 4a clearly indicates that the spectral lines in the visible region of Er3+ are situated in the green region only, so it possesses good color coordination. As for the infrared region (see Figure 5), in general, erbium luminescence at wavelengths between 1520 nm and 1558 nm takes place from f-f transitions which have typically atomic-like sharp peaks between the 4I13/2 state manifold and the 4I15/2 manifold. This transition is usually spin forbidden as per selection rules for the electric dipole, while it is allowed for Er3+ in a host matrix due to the interaction with the crystalline field. As is seen from Figure 5a, the main peak in the infrared region is positioned at 1531 nm and the side peak is at 1545 nm. These emissions are characteristic emissions due to the intra-4f transitions between the 4I13/2 and 4I15/2 manifolds of Er3+ ions. As mentioned above, on viewing the contour map of the luminescence spectral temperature and wavelength one frequently recognizes the trace impurities of rare-earth ions efficiently change the emission spectra of photoluminescence. Photoluminescence spectra of Er3+ doped CaSnO3 reveal that they have a general pattern where the main emission peak at 1531 nm is predominantly in the form of narrow line rare earth emission at lower temperature (i.e 50K). Figures 6 a and b show the PL emission lines for Er doped CaSnO3 at room (300K) and low (10K) temperatures using Si and InGaAs detector. For both temperatures it was observed that the main emission peak in the green region splits into several small peaks. We note that no spectral shift of the emission bands were detected from 10-300K, as expected, because there is shielding of the electronic transitions in the 4f6 configuration of Er ions from 5s25p6 electrons that form two completely filled shells 5s25p6. On the other hand, the PL spectra for NIR region

are very sensitive to the temperature. The normalised emission spectra are shown in Figure 6 b. The observed narrowing of the PL line width of the fine structures at low temperature PL spectra is due to the lack of the phonon assisted transitions by crystalline field of the host material. As mentioned above, on viewing the contour map of the PL spectral intensity and temperature, the PL spectra fine structures make it possible to identify Stark splitting levels of the 4I15/2 state in Er3+ ions. The emission peaks due to Stark splitting levels of the 4I15/2 state in Er3+ ions are clearly seen at 10 K (see Figure 6 b). Figure 7 shows typical PL spectra of CaSnO3:Er3+ as a function of laser power. Emission spectra were recorded by varying the laser power from 2 to 30 mW. It is worth noting that there is not any observable change in the PL signal except for the intensity of the emission lines. This seems reasonable considering that when a higher laser power is applied the light penetration increases.

3.2.3 Sm3+ emission spectra Figures 8a and b display the photoluminescence spectra for Sm3+ doped CaSnO3 as an isometric presentation of PL measurement displaying the intensity (in arbitrary units) versus temperature versus wavelength, recorded between 500 and 1500 nm. It is clearly seen that the sample displayed a variety of luminescence emission lines corresponding to characteristic transitions of the Sm3+ ion. There is no direct evidence of the role for any broad band emission, as would be the characteristic of the pure host lattice. This is most likely related to strong coupling between the emissive centers at the host and Sm3+ energy levels. Figures 9a and b show 2D (color coded plots) contour plots of Sm doped CaSnO3 in the region of VIS and NIR region corresponding to 3-D spectra illustrated in Figure 8. It is equally clear that there are differences

in intensity between near room temperature and 10 K. Indeed, the contour plots of the lower temperature Sm3+ signals of Figures 8a and b for both VIS range and IR region differ significantly and visual inspection immediately reveal that it has a general pattern where the luminescence signals show narrow line rare earth emission features (not shown here). The details of the emission spectra are shown in Figure 9 for data taken at 300 and 10 K. Figure 9a indicates that the relative intensities of the components change on cooling, and in particular the orange components near 650 nm (4G5/2→6H9/2) are increased as the temperature is decreased. For the CaSnO3:Sm3+ phosphor, four prominent groups of emission lines appear at 564, 600, 646, 714, and 784 (weak) nm as seen in Figure 9a. Sm3+ ions show a number of narrow characteristic emission lines which change in wavelength and relative intensities as a function of temperature. They are respectively assigned to the electronic transitions of 4G5/2 → 6HJ, (J=5/2, 7/2, 9/2, 11/2, 13/2) states because of their consistent luminescence behaviours with the Sm3+ emission characteristics (Ruijin et al., 2014;Sheng et al., 2012; Zhang et al., 2012; Park, 2012). The 4

G5/2→6H5/2 transition in the green region is magnetic dipole allowed transition with selection

rule J=0 and ±1. This transition only occurs when Sm3+ is inclined to occupy a particular site within the crystal structure coinciding with the centre of symmetry. The 4G5/2 →6H9/2 transition in the red region is electric dipole allowed transition obeying the selection rule J=2, while Sm3+ is located at the lattice site that lacks center of inversion symmetry (Raju and Buddhudu, 2008; Singh et al., 2010). Among them, the strongest orange 4G5/2→6H7/2 transition (partly magnetic and partly forced electric dipole transition) at 600 nm indicates that the surrounding coordinate of Sm3+ is symmetric and can be used as potential orange-red emitting display materials. Sm3+ mainly took up symmetry center lattice because 4G5/2→6H7/2 transition was stronger than 4

G5/2→6H9/2 transition. Generally speaking as the intensity of the electric dipole transition is

decreased the asymmetric nature becomes lower. Notably, increase in the intensity of the electrical dipole transition can result in much asymmetry nature (Xia and Chen, 2010). The present work demonstrates that the red luminescence (646 nm) attributed to the 4G5/2→6H9/2 transition in the Sm3+ ion is more intense than green emission (564 nm) assigned to the 4

G5/2→6H5/2 transition indicating the asymmetric nature of the CaSnO3 host matrix investigated

here. Such observations are well documented in the literature, where it was established that the relative intensities of the transitions mentioned above provide some information about the local symmetry. The greater value of this ratio gives rise to more distortion from the inversion symmetry. For example, when taking into consideration photoluminescence of Sm 3+-doped Sr2SiO4, it was observed that the value of the obtained ratio remained nearly constant between 5.65 and 6.48. This finding confirms that it would be reasonable to regard the Sm3+ ions as quite distorted environment around cation in Sr2SiO4 structure (Ha et al., 2012). In the infrared region from 850 to 1500 nm, (Figure 9b), splitting emission signals were detected with peaks located at around 904, 1027-1038 and 1156-1185 nm. The emissions are assigned to transitions from 4G5/2 to 6FJ (J = 32, 7/2 and 9/2) and 6F7/2 →6H5/2, respectively. Note that when we have some difficulties to differentiate between possible transitions, then two are given, for example say 1156-1185 nm. The transitions presented here are in good agreement with the literature data (Yamashita and Asano, 1987; Jing et al., 2009). An obvious feature in the infrared region as seen in Figure 9 b is that there is a detectable difference in the fine structures of the crystal field splitting between room and 10K temperatures. Note that the PL signals of Sm3+ doped CaSnO3 phosphor material exhibit the same pattern with increasing laser power (not shown here) as in Er3+ doped one.

3.2.4

Nd3+ emission spectra As mentioned before it is well known that rare earth ions can lead to dramatic changes in

the luminescence character of the material when they are either intentionally (doping Nd, Sm, Er, etc.) or as impurity elements incorporated into the host material. The broad band luminescence signal observed for the reference CaSnO3 is significantly suppressed and replaced by some (but not all) of the internal transitions within the easily and conveniently identifiable schematic energy level diagram of the trivalent lanthanide ions. The suppression of the broad band host lattice emission indicates that the presence of rare earth ions can give rise to further radiative relaxation decay path. Indeed it is not surprising considering that variations caused by each of the changes such as lattice constant, temperature or stress are expected since the different transition energies of the luminescence lanthanide ion (i.e. Nd ion) and relative intensity of the emission lines are fully sensitive to the crystal field at the local site of the host lattice. Dopant interactions with other impurities or intrinsic defects, and presence of dislocations will also have an influence on the spectra of photoluminescence. As seen in Figures 10 a and b which present a characteristic group of lines in the visible range and near infrared region with a laser excitation of 472 nm, the spectral changes observed in photoluminescence with temperature can readily be envisioned from the 3 dimensional (isometric) plots. It is easy to choose different viewing directions in Figure 10 in order to bring to light key features which would otherwise be hidden. Besides, monitoring the PL spectra and showing the results as intensity contour map as a function of temperature and emission wavelength reveals much new insight into understanding of the PL processes from the Nd doped CaSnO3. Nd3+-doped materials usually display NIR emission. The room and low temperature (10K) luminescence signals are given below for comparison purposes and it is seen that most of

the emission at both temperatures are in the infrared region. However, we observe the emission of CaSnO3:Nd3+ phosphor over the wavelength range from VIS to NIR. Figure 11a shows PL data recorded for CaSnO3:Nd3+ phosphor using Si detector which covers from 500 nm to 1000 nm. Four weak PL bands peaking at ~490, 546, 600-665 and 696 nm are observed in the 475– 725 nm regions, which can be related to the transfers of 4G9/2, 2G7/2, 4H11/2, and 4F9/2→4I9/2, respectively [38]. Figures 11 a and b display PL spectrum of CaSnO3:Nd3+ phosphor in the NIR region. Photoluminescence analysis clearly show that there are three strong emission bands located at 860-940, 1045-1137, and 1320-1400 nm attributed to the transitions from 4F3/2 to 4I9/2, 4

I11/2, and 4I13/2 in Nd3+, respectively (Dieke, 1968). In order to clarify the luminescence

mechanism of CaSnO3:Nd3+ phosphors in VIS and NIR regions the aforementioned energy level transitions of Nd3+ is shown in Figures 11 a and b. Nd3+ ion energy level is attributed to 4f3 electronic configuration (i.e. 4I9/2 free ion ground state). There are several clearly resolved photoluminescence peaks assigned to the f-f internal orbital transitions of Nd3+ ions with Stark splitting. Therefore, the observed multiplet emission transitions in Figure 11b are from the Stark levels R1 and R2 of the 4F3/2 manifolds to 4I9/2(Z1–5), 4I9

11/2(Y1–6)

and 4I13/2(X1–7) manifolds

(Nash et al.; 2009).

4.

Conclusions

Based on the experimental results, several conclusions may be highlighted below: I.

Conventional solid state reaction technique has been employed for the synthesis of novel Er3+, Nd3+ and Sm3+. XRD analysis revealed the formation of the CaSnO3 phase of all trivalent rare earth doping

II.

The samples were characterized by PL measurements as function of temperature and laser power in visible and infrared region. It was observed that the use of different rare

earth ions results in important effects on the PL emission spectrum as the change of ionic radii would perturb the overall defect complex. Moreover if the complex is extensive, it may well provide an interaction among several very close neighbours (i.e., not just one rare earth dopant) and this would amplify the ion size distortions of the complex. It is noteworthy that there is evidence of paring or clustering of rare earth dopants in many rare earth cases. III.

PL or other forms of ionization would alter some of the components of intrinsic defect complexes in CaSnO3, but not trivalent rare earth ions. Therefore we suggest that the observed luminescence lines for the different rare earth ions are characteristic of the 3+ state, and would depend on the orbital rearrangements within the complex.

IV.

The experimental results show that Er3+, Nd3+ and Sm3+ doped CaSnO3 phosphors exhibit infrared, orange-red, and green emissions lines. Although there are not previous studies in the literature, our results suggest that there are some differences in the energy transfer rate into the various excited states of the rare earth ion.

V.

PL results have revealed that such materials are interesting systems for remarkable application prospects due to their excellent luminescence properties. Further investigations are in progress to understand the effect of the synthesis routes by using different techniques.

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Zhu, M., Yang, C., 2013. Blue fluorescent emitters: design tactics and applications in organic light-emitting diodes.Chem. Soc. Rev. 42, 4963-4976. FIGURE CAPTIONS Figure 1. X-ray diffraction patterns of (a) the JCPDS card No. 77-1797, (b) undoped CaSnO3 (c) CaSnO3:Nd3+ sample (d) CaSnO3:Er3+ sample and (e) CaSnO3:Sm3+ sample calcined at 1200 °C for 2 hours. Figure 2. The laser power dependence of the PL signals for pure CaSnO3 at (a) 10 K and (b) 300 K using a Si detector. Figure 3. (a) Isometric and (b) contour map of the PL of undoped CaSnO3 using a Si detector and a 474 nm excitation line of a blue emitting laser. Figure 4. Low temperature PL from Er3+ doped CaSnO3 using a Si detector. (a) Isometric view and (b) contour map, which emphasizes that different spectral regions peak in intensity at different temperatures. The excitation was made using 474 nm line of a blue emitting diode laser. Figure 5. (a) Isometric and (b) contour map of the PL of Er3+ doped CaSnO3 using an InGaAs detector and a 474 nm excitation line of a blue emitting laser. Figure 6. PL spectra recorded for Er3+ doped CaSnO3 at 300 K and 10 K in which measurements were taken using (a) Si and (b) InGaAs detectors. Figure 7. PL spectra of CaSnO3 doped with Er3+ with (a) Si and (b) InGaAs detectors at 300 K, and (c) Si and (d) InGaAs detector at 10 K with different laser powers from 2 mW to 30mW. Figure 8. Isometric views of low temperature photoluminescence from CaSnO3:Sm3+ with (a) Si and (b) InGaAs detectors. The excitation was made using 474 nm line of a blue emitting diode laser.

Figure 9. PL spectra for Sm3+ doped CaSnO3 at 300 K and 10 K recorded using (a) Si and (b) InGaAs detectors. Figure 10. Isometric views of low temperature photoluminescence from CaSnO3:Nd3+ with (a) Si and (b) InGaAs detectors. The excitation was made using 474 nm line of a blue emitting diode laser. Figure 11. PL spectra for Nd3+ doped CaSnO3 at 300 K and 10 K recorded using (a) Si and (b) InGaAs detectors.

Highlights  Characteristic and photoluminescence properties have been investigated.  Several sharp and strong emission bands due to rare earth ion were observed for rare earth doped sample.  The nature and limitation of the interaction between CaSnO3 and the activator ions were

discussed.

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