Blue to magenta tunable luminescence from LaGaO₃: Bi³⁺, Cr³⁺ doped phosphors for field emission display applications

Abstract

A series of blue to magenta emitting color-tunable LaGaO₃: Bi³⁺/Cr³⁺ phosphors were prepared by chemical routes, and their phase structure, morphology and photoluminescence (PL) properties were investigated in detail. Luminescence studies indicated that the optimum concentrations of Bi³⁺ and Cr³⁺ in LaGaO₃ were found to be 1 at% and 3 at%. Co-doping with Bi³⁺ ions resulted in increased Cr³⁺ emission intensity and gradual reduction in Bi³⁺ emission intensity, confirming the presence of a Bi³⁺–Cr³⁺ energy transfer. The energy transfer (ET) mechanism from the host lattice to the Bi³⁺ and Cr³⁺ ions in the LaGaO₃: Bi³⁺/Cr³⁺ phosphor has been explained. The ET efficiency has been calculated and found to be 55%. The critical ET distance has been calculated by the concentration-quenching method. The enhanced intensity and tuned luminous color of LaGaO₃: Bi³⁺/Cr³⁺ phosphors provided a promising material for field emission display devices.

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Introduction

Currently, oxide-based perovskite phosphors are strategic components for display applications, described by the general chemical formula ABO₃. Research on these materials opens a variety of new possibilities in the field of flat panel display devices, which can be integrated into various types of displays such as plasma display panels (PDPs), vacuum fluorescent displays (VFDs), electro-luminescent displays (EDs) and field emission displays (FEDs).^1–7 In comparison to conventional phosphors for cathode ray tubes (CRT), it is important to develop phosphors for display devices that show high efficiency and good stability at low-voltage electron excitation and high current density.^5–9 Therefore, selection of suitable phosphors material is considered to be one of the most critical and urgent challenges in the lighting field. It is well known that besides from its luminescence applications, LaGaO₃ perovskite have been promising material as an electrolyte for solid fuel cells.^10,11 The lanthanum gallate (LaGaO₃) crystal has an orthorhombically distorted centrosymmetric GdFeO₃ type perovskite-like structure with space group Pbnm.¹² Indeed, LaGaO₃ is a relatively simple matrix, which consists three dimensional sub-lattice of corner connected GaO₆ octahedra and the La³⁺ is in eight-fold coordination with oxygen ions, and is potentially act as a host material in phosphor applications. LaGaO₃ doped with several rare earth (RE) ions (RE = Eu, Tb, Dy/Eu, Sm/Tb etc.) were extensively studied for their luminescence properties, color rendering properties and superior stability under electron bombardment.^13–15 The luminescent properties of Bi³⁺ doped LaGaO₃ were studied by B. Jacquier et al.¹⁶ reported that Bi³⁺ was a good activator of luminescence for lanthanide compounds having its transitions between the ground state ¹S₀ and the excited levels ³P₁ and ¹P₁. Alok M. Srivastava et al.¹⁷ reported thermal quenching of Bi³⁺ luminescence in LaGaO₃ and explained the energy transfer mechanism between Bi³⁺ ions to host lattice-quenching centers. Research reports also show that along with Eu²⁺, Ce³⁺; Bi³⁺ could be used as sensitizer ion to produce abundant and tunable emission colors including white via adjusting doped ion concentrations.^18–22 Trivalent chromium (Cr³⁺) is widely used as a luminescent dopant in various materials. Chromium is a low-cost activator, which can provide deep red color and bright luminescence. On this account, Cr³⁺ is the subject of numerous optical spectroscopic, vivo imaging, energy saving and luminescence applications.^23–26 Recently, significant efforts have been devoted by several research groups on the synthesis and characterization of various Cr³⁺ doped host materials.

Our present studies have paid more attention to investigate NIR photoluminescence of Cr³⁺ ions doped LaGaO₃ phosphors and also including the enhancement in intensity of Cr³⁺ ions on co-doping with Bi³⁺ ions in detail. To the best of author's knowledge, no accurate information is available on the energy transfer (ET) mechanism and efficiency from Bi³⁺ to Cr³⁺ in LaGaO₃ compound. From CIE color coordinates, it is demonstrated that, by carefully selecting Bi³⁺ and Cr³⁺ contents, the relative intensity of the different emissions can be changed producing an overall emission colour that can be tuned from blue to magenta.

Experimental details

Preparation of the nanoparticles

The LaGaO₃ undoped, LaGaO₃: (0.1, 0.5, 1, 2 at%) Bi³⁺, LaGaO₃: (0.5, 1, 3, 5 at%) Cr³⁺ and LaGaO₃: (1 at%) Bi³⁺, (0.5, 1, 3, 5 at%) Cr³⁺ phosphors were all prepared by the polyol mediated method. Stoichiometric amounts of La(NO₃)₃·6H₂O (Sigma-Aldrich, 99.99%), Ga(NO₃)₃·H₂O (Sigma-Aldrich, 99.99%), Bi(NO₃)₃·5H₂O (Sigma-Aldrich, 99.99%), Cr(NO₃)₃·9H₂O (Alfa Aesar 98.5%) are used as precursors. Ethylene glycol (MERCK, 99.99%) was used as a solvent and stabilizing ligand. For preparing the undoped lanthanum gallate (LaGaO₃), initially stoichiometric amounts of La(NO₃)₃·6H₂O and Ga(NO₃)₃·H₂O was transferred into a two-necked RB flask containing solution of 20 ml ethylene glycol. The solution was kept under magnetic stirring and continuous heating. When the temperature was at 100 °C, around 2 gram urea was added and temperature was raised further to 120 °C and kept up at this temperature for 2 hours. The formed precipitate was cooled, centrifuged, washed thrice with methanol, twice with acetone and allowed to dry overnight at room temperature. Then the samples were sintered in a muffle furnace at a temperature of 1000 °C for 5 h. Finally, the samples are naturally cooled down to room temperature and fully ground for further investigations. The above procedure was repeated for the preparation of Cr and Bi/Cr, doped LaGaO₃ samples by dissolving required amount of Cr(NO₃)₃·9H₂O, and Bi(NO₃)₃·5H₂O salts in ethylene glycol.

Characterization

X-ray diffraction (XRD) studies were carried out using a Philips powder X-ray diffractometer (model PW 1071) with Ni filtered Cu-Kα radiation. For calibration purpose, diffraction peak corresponding to the (111) plane of Si at a 2θ value of 28.442° was employed. The lattice parameters were obtained from refinement of the XRD patterns using POWDERX software. All steady-state luminescence and lifetime measurements were carried out at room temperature using an Edinburgh Instrument (FLSP 920 system) having a 450 W Xe lamp. A microsecond flash lamp and a nanosecond hydrogen flash lamp were used for lifetime measurements. All emission and excitation measurements were carried out with a resolution of 3 nm. Emission spectra were corrected for the detector response and excitation spectra for the lamp profile. The fundamental structural morphologies of the samples and the elemental composition investigation has been done by utilizing a field emission scanning electron microscope FE-SEM Supra 55 (Carl Zeiss, Germany). An accelerating voltage of 20 kV and magnification of 10k× was used for recording the micrographs.

Results & discussion

Phase formation and microstructure

Fig. 1(a) shows the XRD patterns of undoped LaGaO₃, LaGaO₃: 1 at% Bi³⁺, LaGaO₃: 3 at% Cr³⁺ and LaGaO₃: 1 at% Bi³⁺, 3 at% Cr³⁺ phosphors. From Fig. 1(a), all the diffraction peaks are in good agreement with the reported orthorhombic phase of LaGaO₃ (PCPDF89-7946)¹⁹ and no second phase was detected indicating that the Bi³⁺ and Cr³⁺ completely dissolved in the LaGaO₃ host lattice. Table 1 shows lattice parameters and unit cell volume calculated from the peak position of XRD patterns from the undoped and doped LaGaO₃ samples whereas average particle size where calculated from the peak width (i.e. FWHM) of the most intense peak (110) at 2θ = 32.49° from the XRD pattern using Scherrer's equation (D = 0.9λ/β cos θ, where D is the average particle size, λ is the wavelength of X-rays and β is the corrected full width at half maximum (FWHM) of an observed peak). The average crystallite size (D) of pure LaGaO₃, doped and co-doped LaGaO₃ particles which are annealed at 1000 °C are estimated in the range of 70–80 nm. LaGaO₃ structure shown in Fig. 1(b) consists of slightly distorted and tilted GaO₆ octahedra are linked to each other by corner sharing to form three-dimension network and the La³⁺ is in eight-fold coordination with oxygen ions. The average bond length of Ga–O in GaO₆ is 1.975 Å; while La³⁺ is 8-coordinated by O atoms with average bond length of 2.62 Å for La–O. The minor changes in lattice parameters of single doped Bi³⁺, Cr³⁺ and co-doped in LaGaO₃ when compared with undoped LaGaO₃ depends on ionic radii.²² The radius of Bi³⁺ (r = 1.03 Å, coordination number, CN = 6) is similar to that of La³⁺ (r = 1.16 Å, CN = 8), while the radius of Cr³⁺ (r = 0.61 Å, CN = 6) is comparable to that of Ga³⁺ (r = 0.47 Å, CN = 6),²⁷ thus in Bi³⁺–Cr³⁺ co-doped LaGaO₃, Bi³⁺ mostly likes to take La site and Cr³⁺ likes to take Ga site. SEM image of the selected LaGaO₃: 1 at% Bi³⁺, 3 at% Cr³⁺+ phosphor is presented in Fig. 1(c). It is clearly seen that the sample is composed of aggregated particles with size ranging from 60 to 90 nm. The approximate spherical morphology and particles size confirms that these phosphors can be used potentially in the future field emission display device applications.

Fig. 1 (a) XRD patterns of LaGaO₃, LaGaO₃: Bi³⁺, LaGaO₃: Cr³⁺, LaGaO₃: Bi³⁺, Cr³⁺ samples (b) 3D crystal structure of LaGaO₃ and (c)FE-SEM image of LaGaO₃: (1 at%) Bi³⁺, (3 at%) Cr³⁺ sample.

Table 1 Lattice parameters of LaGaO₃, LaGaO₃: 1 at% Bi³⁺, LaGaO₃: 3 at% Cr³⁺ and LaGaO₃: 1 at% Bi³⁺: 3 at% Cr³⁺ phosphors

Compositions	a (Å)	b (Å)	c (Å)	V^3 (Å)
LaGaO3	5.478	5.594	7.659	234.70
LaGaO3: 1 at% Bi^3+	5.468	5.552	7.691	233.48
LaGaO3: 3 at% Cr^3+	5.483	5.617	7.652	235.66
LaGaO3: 1 at% Bi^3+, 3 at% Cr^3+	5.473	5.563	7.644	232.73

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Photoluminescence and energy transfer (ET) mechanism of the samples

Excitation (inset) and emission spectra of host LaGaO₃ at room temperature shown in Fig. 2, with excitation at 250 nm, host LaGaO₃ gives a wide band from 300 to 600 nm with a maximum peak at 428 nm, which is attributed to the transition of self-activated optical center corresponding to groups in the host lattice GaO₆.²⁸ Monitored at 428 nm (inset), the corresponding excitation spectra in the range of 200–300 nm is observed with maximum peak position at 428 nm.

Fig. 2 Emission spectra and excitation (inset) of LaGaO₃ phosphor.

The excitation (inset) and emission spectra of a samples LaGaO₃: (0.1, 0.5, 1, 2) at% Bi³⁺ is shown in Fig. 3(a), it is observed that the emission band centred at ∼374 nm which is attributed to ³P₁–¹S₀ transition of Bi³⁺ ion on excitation with 309 nm.

Fig. 3 (a) Emission spectra and excitation (inset) spectra of LaGaO₃: Bi³⁺ phosphor (b) decay curve for LaGaO₃: Bi³⁺ phosphor excited at 309 nm and monitored at 374 nm.

With increasing Bi³⁺ concentration, the intensity of the 374 nm emission band increases and reaches a maximum at 1 at% and decreases when Bi³⁺ content is further increased due to concentration quenching effect. Hence, multiphonon relaxation and the cross relaxation between neighboring Bi³⁺ ions, substantially quench the photoluminescence.²⁹ Hence, the optimized Bi³⁺ content is at x = 1 at%. This is also confirmed from the corresponding bi-exponential lifetime decay values (152.52 ns, 168.26 ns, 201.12 ns, 142.03 ns) and curves of Bi³⁺ ions in LaGaO₃ which is shown in Fig. 3(b)³⁰ (procedure for calculation of decay values shown in preceding sections).

The excitation spectra shows weak band around 255 nm due to the charge transfer (CT) transition of 2p orbital of O²⁻to the empty 4s orbital of Ga³⁺ because the 3d orbital is completely filled³¹ and another is at 309 nm due to ¹S₀–³P₁ electron transition of Bi³⁺ ion respectively. And overlapping of the absorption band of ¹S₀–¹P₁ state of Bi³⁺ ions and the (O–Ga) CT transition is also observed.¹⁶ Emission band of host LaGaO₃ is found to overlap with excitation band of LaGaO₃: 1 at% Bi³⁺ phosphor in the range of 275–350 nm, so, energy transfer (ET) between Bi³⁺ ion and GaO₆ group may be formed shown in Fig. 1S.† In addition, it is worth to note that LaGaO₃: 1 at% Bi³⁺ phosphor with excitation around 309 nm does not show host emission band assigned to Ga³⁺–O²⁻ transition because the excited electrons in GaO₆ group directly transfer the energy from the conduction band level of GaO₆ to higher excited level of Bi³⁺ ion by energy transfer process.

Fig. 4(a and b) shows the emission and excitation spectra of LaGaO₃: (0.5, 1, 3, and 5 at%) Cr³⁺ phosphor. Under excitation at 453 nm, the sample exhibits a broadening ²E → ⁴A₂ emission peaking at 740 nm ranging from _∼650 to 800 nm. The broadening of the ²E → ⁴A₂ emission is possibly caused by the electron-phonon coupling in the host lattice. The excitation spectrum shown in Fig. 4(b) monitored at 740 nm covers a very broad spectra ranging from 200 to 700 nm and consists of three excitation bands originating from the d–d inner transitions of Cr³⁺, i.e., 262 nm band originating from the ⁴A₂ → ⁴T₁ (te²) transition, the 453 nm band originating from the ⁴A₂ → ⁴T₁ (t²e) transition and the 617 nm band originating from the ⁴A₂ → ⁴T₂ (t²e/²E) transition.^32,33 In addition to this, (Fig. 4(a) inset) shows the variation in the Cr³⁺ concentration-dependent PL intensities, and the optimum doping concentration was found at y = 3 at%.

Fig. 4 (a) Emission spectra (inset: PL intensity dependence on Cr³⁺ content) (b) excitation spectra of LaGaO₃: Cr³⁺ phosphor excited at 453 nm and monitored at 740 nm. (c) Schematic diagram of the photoluminescence showing the excitation, electron transitions of Cr³⁺ in LaGaO₃: Cr³⁺ phosphor.

After that, the PL intensity begins to reduce owing to the concentration quenching effect of Cr³⁺ ions. Furthermore, a schematic diagram of the related energy levels for LaGaO₃: Cr³⁺ phosphors is depicted in energy level diagram Fig. 4(c). As for the photoluminescence process, under light excitation corresponding to different wavelength, such as 261 nm, the ground-state electrons of Cr³⁺ ions are promoted to the ⁴T₁ (te²) level. The excited electrons will relax to the ²E energy level, and shows the near Infra-Red emission via the ²E → ⁴A₂ transition. The corresponding bi-exponential average lifetime decay values and curves of Cr³⁺ ions (1.48 ms, 3.26 ms, 3.91 ms, 2.14 ms) in LaGaO₃ which is shown in Fig. 5. The efficient ET needs to have a significant spectral overlap between the emission bands of undoped and Bi³⁺ doped LaGaO₃, Fig. 2S† to excitation bands of LaGaO₃: 3 at % Cr³⁺ nanophosphor, in the range of 250–800 nm. Thus it can be speculated that in the co-doped LaGaO₃, the energy transfer from GaO₆ to Cr³⁺ and Bi³⁺ to Cr³⁺ may occur.

Fig. 5 Average Life time decay curve and values for LaGaO₃: Cr³⁺ phosphor excited at 453 nm and monitored at 740 nm.

In Fig. 6(a), it is observed that the emission spectrum of LaGaO₃: 1 at% Bi³⁺, (0.5, 1, 3, 5 at%) Cr³⁺ contains both Bi³⁺ emission and Cr³⁺ emission when excited at 309 nm. When Bi³⁺ concentration was fixed at 1 at%, and varying the Cr³⁺ concentration, the emission intensity of Cr³⁺ reaches maximum upto 3 at% and then notably decrease of Cr³⁺ emissions is observed on increasing further concentration, which can be rationalized as concentration quenching. From the excitation spectra (inset) (monitored at 740 nm) Fig. 6(a), broad band ranging from (200–400 nm) peak maximum at ∼309 nm is observed which is due to Bi³⁺ ion absorption and peaks around (weak) ∼260 nm, (broad) ∼453 nm are due to d–d transitions of Cr³⁺ ions. Meanwhile, Bi³⁺ emission decreases gradually, and this phenomenon ascribed to energy transfer happened between Bi³⁺–Cr³⁺ in this system. The relative emission intensities of Cr³⁺ ions at 740 nm and Bi³⁺ ions at 374 nm as a function of Cr³⁺ concentration were shown in Fig. 6(b). In addition it is observed that on excitation with 309 nm along with Bi³⁺, Cr³⁺ characteristic emissions there is weak host emission around ∼450 nm which is due to GaO₆ transitions, which is overlapped with Bi³⁺ ion emission as shown in (Fig. 6(a)). Since the emission band of the LaGaO₃ host overlaps with the excitation band of Bi³⁺, Cr³⁺ ions, the excited electron gets transfer their energy from GaO₆ group directly to Cr³⁺ and Bi³⁺ ions. Later, the excited electrons in Bi³⁺ ion then relaxes where some part of energy has been released in the form of 374 nm light and the other part was contributed by the energy transfer process from Bi³⁺ to the Cr³⁺.

Fig. 6 (a) Emission and excitation (inset) spectra of LaGaO₃: 1 at% Bi³⁺, 3 at% Cr³⁺ phosphor (b) intensity variation of Bi³⁺ as a function of Cr³⁺ concentration (c) intensity enhancement of Cr³⁺ ions on Bi³⁺ co-doping via energy transfer between Bi³⁺–Cr³⁺.

At the same time, we also illustrated the emission profiles (λ_ex = 453 nm) of Cr³⁺ ion with and without Bi³⁺ ion presence in host for verifying the intensity enhancement in Cr³⁺ emissions due to Bi³⁺–Cr³⁺ energy transfer shown in Fig. 6(c). The energy transfer from Bi³⁺ to Cr³⁺, results in the improvement of Cr³⁺ emission, which is also strongly supported by the decrease in the decay behaviour of the Bi³⁺ emission in co-doped samples.

Decay curves of Bi³⁺ with various Cr³⁺ content for the system LaGaO₃: 1 at% Bi³⁺, (0.5, 1, 3, 5 at%) Cr³⁺ are illustrated in Fig. 7(a and b). The decay curves were well fitted with a double-exponential rule according to the following equation:

where, I is the luminescence intensity at the time t, τ₁ and τ₂ are two components of the decay time, A₁ and A₂ are constants. According to these parameters, the average decay times of LaGaO₃: 1 at% Bi³⁺, (0.5, 1, 3, 5 at%) Cr³⁺ nanophosphors can be calculated according to the following formula:³⁴

Fig. 7 (a) Decay curve for Bi³⁺ ions in LaGaO₃: 1 at% Bi³⁺, (0.5, 1,3,5 at%) Cr³⁺ phosphor excited at 309 nm and monitored at 374 nm (b) decay curve for Cr³⁺ ions in LaGaO₃: 1 at% Bi³⁺, (0.5, 1,3,5 at%) Cr³⁺ phosphor excited at 309 nm and monitored at 740 nm.

Decay times (τ) of Bi³⁺ calculated are about 180.12, 153.25, 127.21 and 90.72 ns for Fig. 7(a) LaGaO₃: Bi³⁺ (1 at%), (0.5, 1, 3, 5 at%) Cr³⁺ and corresponding to decay times of 2.27, 3.75, 5.48 and 2.55 ms respectively for varying contents of Cr³⁺ Fig. 7(b).

The increase of Cr³⁺ content leads to faster decay of Bi³⁺ emission, which is attributed to ET from Bi³⁺ to Cr³⁺. The ET efficiency η_T of Bi³⁺–Cr³⁺ can be calculated using the following equation³⁵

where τ_S and τ_S0 represent the lifetime values of sensitizer Bi³⁺ in the presence and absence of Cr³⁺. The energy-transfer efficiency η_T values from Bi³⁺ to Cr³⁺ for LaGaO₃ are tabulated in Table 2. With increasing Cr³⁺ doping concentrations, the energy-transfer efficiency η_T reaches approximately 55%, indicating that the ET from Bi³⁺ to Cr³⁺ is efficient (Table 2). However, it is well-know that the impurities can affect the luminescence properties, but it has the minute influence. Therefore, the interaction type between sensitizers or between sensitizer and activator can be calculated by the following equation³⁶where x is the concentration of the activator ions (Bi³⁺ and Cr³⁺ ions), I is the emission intensity, K and β are constants for the same excitation condition for a given host lattice, and θ is a function of multipole–multipole interaction. When the value of θ is 6, 8, or 10, the interaction types correspond to dipole–dipole (d–d), dipole–quadrupole (d–q), and quadrupole– quadrupole (q–q) interactions, respectively. The dependence of log(I/x) on log(x) was found to be relatively linear, and it yields a straight line with a slope equal to θ/3, so we can obtain the θ value to study the energy-transfer process between Bi³⁺ and Cr³⁺ in LaGaO₃ host. As shown in Fig. 8 the slope of the straight line is −θ/3 = −1.72 based on the PL data of this series of LaGaO₃: 1 at% Bi³⁺, (0.5, 1, 3, 5 at%) Cr³⁺ samples. The calculated value of θ is 5.16, which is close to six, meaning that the dipole–dipole interaction is the dominant mechanism for the interaction of Bi³⁺ and Cr³⁺ in the LaGaO₃ phosphors.

Table 2 Energy transfer efficiency (η_T) of the LaGaO₃: 1 at% Bi³⁺, 3 at% Cr³⁺ phosphor

Concentration (x)	η (%)
0.5	11
1	24
3	37
5	55

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Fig. 8 The fitting line of log (I/x) vs. log(x) in LaGaO₃: 1 at% Bi³⁺, 3 at% Cr³⁺ phosphors beyond the quenching concentration.

Moreover, the critical distance of Bi³⁺ and Cr³⁺ is also an essential parameter if we consider the concentration quenching effect in this system. We can approximately estimate the critical distance from the report of Blasse, the critical distance (R_c) can be calculated as follows³⁶

where V is the volume of the unit cell, Z represents the number of the activator ions in the unit cell, X_c is about 0.04 from the total concentration of Cr³⁺ (the concentration of 0.03) and Bi³⁺ (the concentration of 0.01). For the LaGaO₃ host, the crystallographic parameters are (V = 244.77 Å, Z = 2). The R_c critical transfer distance is determined to be 11.34 Å. This value is much longer than 5 Å, indicating the possibility of energy transfer via the multipolar interaction mechanism, viz, dipole–dipole interaction as mentioned above.

It is worthwhile to notice that the emission band of Bi³⁺ ions is in blue region and the emission band of Cr³⁺ ions is in red region. Combining both of them, magenta light emission may be achieved. Therefore, the luminescent colors of LaGaO₃: Bi³⁺ (1 at%), (0.5, 1, 3, 5 at%) Cr³⁺ phosphors excited by 311 nm are characterized by Commission International de I'Eclairage (CIE) chromaticity diagram and shown in Fig. 9. The Bi³⁺, Cr³⁺ co-doped samples generates the color tunability from blue to magenta due to an efficient energy transfer from Bi³⁺ to Cr³⁺. The CIE chromaticity coordinate of LaGaO₃: Bi³⁺ 1 at%, 3 at% Cr³⁺ sample is calculated to be (0.45, 0.24), i.e. magenta color is obtained from LaGaO₃: Bi³⁺ 1 at%, 3 at% Cr³⁺ sample. The results indicate that Bi³⁺, Cr³⁺ co-doped phosphors may find potential application in field emission display applications.

Fig. 9 CIE chromaticity diagram.

Conclusions

In this study, Bi³⁺ and Cr³⁺ co-doped LaGaO₃ phosphors were prepared by chemical route. XRD proved the orthorhombic phase of LaGaO₃: Bi³⁺, Cr³⁺ phosphors annealed at 1000 °C. The recorded FE-SEM micrograph showed that LaGaO₃: Bi³⁺, Cr³⁺ phosphors were composed of agglomerated and spherical shaped particles. The photoluminescence properties, life time studies and energy transfer process were investigated in detail. The energy transfer from Bi³⁺ to Cr³⁺ was clearly observed and the maximum efficiency found to be 55% from lifetime values. Furthermore, the CIE diagram showed that the colors can be tuned from blue to magenta, indicating that the developed phosphor may potentially be used as a single phase phosphor for field emission display devices.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

The authors are grateful to Dr Sudarsan, Scientist-G, Bhabha Atomic Research Centre (BARC) for PL studies and Dr R. David Kumar, Principal, Government College (A), Rajamahendravaram, Andhra Pradesh for necessary lab facilities. One of the author Dr K. R. Rao gratefully acknowledge DAE-BRNS Project No: 2013/34/22/BRNS/10250 for providing the financial support.

Notes and references

1. H. A. Hoppe, Angew. Chem., Int. Ed., 2009, 48, 3572–3582.
2. I. Shah, Phys. World, 1997, 10, 45–48.
3. B. Chalamala, Y. Wei and B. Gnade, IEEE Spectrum, 1998, 35, 42–51.
4. R. Waser, Nanoelectronics and Information Technology, Wiley-Vch, Weinheim, Germany, 2003, ch. 39.
5. C. E. Hunt and A. G. Chakhovskoi, J. Vac. Sci. Technol., B: Microelectron. Nanometer Struct.–Process., Meas., Phenom., 1997, 15, 516.
6. G. Li and J. Lin, Chem. Soc. Rev., 2014, 43, 7099.
7. S. S. Pitale, V. Kumar, I. M. Nagpure, O. M. Ntwaeaborwa, E. Coetsee and H. C. Swart, J. Appl. Phys., 2011, 109, 013105.
8. X. Liu, L. Yan and J. Lin, J. Electrochem. Soc., 2009, 156(1), 1.
9. S. H. Cho, S. H. Kwon, J. S. Yoo, C. W. Oh, J. D. Lee, K. J. Hong and S. J. Kwon, J. Electrochem. Soc., 2000, 147, 3143.
10. M. I. Martinez-Rubio, T. G. Ireland, G. R. Fern, J. Silver and M. J. Snowden, Langmuir, 2001, 17, 7145.
11. G. Wakefield, E. Holland, P. J. Dobson and J. L. Hutchison, Adv. Mater., 2001, 13, 1557.
12. M. Marti, P. Fisher, F. Altorfer, H. J. Sheel and M. Tadin, J. Phys.: Condens. Matter, 1994, 6, 127.
13. D. Lybye, F. W. Poulsen and M. Mogensen, Solid State Ionics, 2000, 128, 91–103.
14. X. Liu and J. Lin, J. Mater. Chem., 2008, 18, 221–228.
15. X. Liu, R. Pang, Z. Quan, J. Yang and J. Lin, J. Electrochem. Soc., 2007, 154(7), J185–J189.
16. B. Jacquier, G. Boulon, G. Sallavuard and F. Gaume Mahn, J. Solid State Chem., 1972, 4, 374–378.
17. A. M. Srivastava, Mater. Res. Bull., 1999, 34(9), 1391–1396.
18. T. Samuel, C. Satya Kamal, K. Sujatha, V. Veeraiah, Y. Ramakrishana and K. Ramachandra Rao, Optik, 2016, 127, 10575–10587.
19. T. Samuel, C. Satya Kamal, S. Ravipati, B. P. Ajayi, V. Veeraiah, V. Sudarsan and K. Ramachandra Rao, Opt. Mater., 2017, 69, 230–237.
20. P. Ma, Y. Song, B. Yuan, Y. Sheng, C. Xu, H. Zou and K. Zheng, Ceram. Int., 2017, 43, 60–70.
21. J. Y. Park, H. C. Jung, G. S. R. Raju, B. Kee Moon, J. Hyun Jeong, S. M. Son and J. Hwan Kim, Mater. Res. Bull., 2010, 45, 572–575.
22. C. S. Kamal, T. K. Visweswara Rao, P. V. S. S. S. N. Reddy, K. Sujatha, B. P. Ajayi, J. B. Jasinski and K. Ramachandra Rao, RSC Adv., 2017, 7, 9724.
23. Y. Katayama, H. Kobayashi and S. Tanabe, Appl. Phys. Express, 2015, 8, 012102.
24. V. A. Trepakov, Z. Potucek, M. V. Makarova, A. Dejneka, P. Sazama, L. Jastrabik and Z. Bryknar, J. Phys.: Condens. Matter, 2009, 21, 375303–375308.
25. V. Singh, G. Sivaramaiah, J. L. Rao and S. H. Kim, Mater. Res. Bull., 2014, 60, 397–400.
26. Z. Han, X. Li, J. Ye, L. Kang, Y. Chen, J. Li and Z. Lin, J. Am. Ceram. Soc., 2015, 98(8), 2336–2339.
27. R. D. Shannon, Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr., 1976, 32, 751–767.
28. N. V. Chezhina, E. V. Bodritskaya, N. A. Zhuk, V. V. Bannikov, I. R. Shein and A. L. Ivanovskii, Phys. Solid State, 2008, 50, 2121–2126.
29. M. C. Wang, H. J. Lin and T. S. Yang, J. Alloys Compd., 2009, 473, 394–400.
30. G. Blasse and A. Bril, J. Inorg. Nucl. Chem., 1967, 29, 266.
31. G. Blasse and B. C. Grabmaier, Luminescent materials, Springer-Verlag, Berlin, 1994.
32. P. D. Rack, J. J. Peterson, M. D. Potter and W. Park, J. Mater. Res., 2001, 16, 1429–1433.
33. M. Grinberg, Opt. Mater., 2002, 9, 37–45.
34. C. H. Huang, T. W. Kuo and T. M. Chen, ACS Appl. Mater. Interfaces, 2010, 2, 1395.
35. W. H. Di, X. J. Wang, P. F. Zhu and B. J. Chen, J. Solid State Chem., 2007, 180, 467.
36. G. Blasse, Phys. Lett. A, 1968, 28(42), 444–445.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c7ra08864g

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