Dy³⁺ Doped Ca₉Gd(PO₄)₇: a novel single-phase full-color emitting phosphor

Abstract

A series of un-doped and Dy³⁺ doped Ca₉Gd(PO₄)₇ phosphors were synthesized by traditional solid state reactions. X-ray diffraction analysis and scanning electronic microscope observation were carried out to examine the phase formation and morphology of prepared samples. Emission spectra under the excitation at 350 nm ultraviolet light turn out that main emission bands are located at 480, 570 and 659 nm, which can be assigned to the optical transitions ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → ⁶H_11/2 of Dy³⁺, respectively. Comparison of emission spectra upon excitation of 273 nm between un-doped and Dy³⁺ doped Ca₉Gd(PO₄)₇ samples proves that effective energy transfer from Gd³⁺ to Dy³⁺ takes place. The Commission International de I’Eclairage color coordinates (0.272, 0.322) located in white region was achieved. With the increasing doping concentration of Dy³⁺, concentration quenching is clearly observed and the optimum content of doped Dy³⁺ is 0.12. The mechanism of concentration quenching is experimentally ascertained to be electric dipole–dipole interactions. The study of quantum efficiency and thermal stability shows that our phosphors have higher quantum efficiency and better thermal stability. This work indicates that our phosphors have potential applications in white light-emitting diodes.

1 Introduction

Nowadays, white light-emitting diodes (wLEDs) have obtained extensive applications in lighting, display, plant growth regulation and in situ imaging of organisms because of their advantages of energy saving, environmental friendliness, high efficiency, long life, and so on [1,2,3]. Combination of a single LED chip with a single phosphor might be the simplest approach to obtain white light. Based on this point of view, the first method has been widely used, namely, combining a blue LED chip with a yellow phosphor (YAG: Ce³⁺). White light obtained by this method has some vital drawbacks such as halo effect due to the different emission characteristics of the LEDs (directional) and the phosphors (isotropic), low color rendering index (CRI) and high color temperature caused by lack of red component in the spectra [4, 5]. The second method, that is, combining an ultraviolet (UV) LED chip with a full-color phosphor, is also being widely studied. At present, the market share of white light obtained by this method is obviously inferior to that by the first method. However, people are still investing a lot of energy in this area, hoping to get some full-color phosphors with excellent performing [6, 7].

Dy³⁺ doped inorganic compounds are a kind of full-color phosphors that can be excited by an UV LED chips. In the past several decades, numerous studies have proved their application value and development potential [8,9,10]. Dy³⁺ is of great importance among the rare earth ions because of its 4f–4f transitions which lead to blue, yellow and red emission. The luminescence lines are located in the regions of 470–500, 570–600, and 650–680 nm due to the optical transitions ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → ⁶H_11/2 of Dy³⁺, respectively. Besides, it is well known that the emission light is different in color. This depends on whether the Dy³⁺ ions are located at the high-symmetry sites with inversion centers or the low-symmetry without inversion centers [11, 12]. Additionally, gadolinium ion is a good constituent cation in host crystals which can be substituted by other rare earth ions. More importantly, Gd³⁺ can emit UV light at around 310 nm under the excitation at 275 nm [13]. Energy transfer from Gd³⁺ to Dy³⁺ might occur in a single phase. Recently, single-phase full-color emitting phosphors for wLEDs with a phosphate as host have obtained exclusive attention because of their high thermal stability and low preparation cost. Up to date, many research groups have paid many efforts to phosphors based on phosphates hosts, such as Ca₉Lu(PO₄)₇: Eu²⁺, Mn²⁺ [14], CaZr₄(PO₄)₆: Dy³⁺ [15], Na₃Bi(PO₄)₂: Tb³⁺, Sm³⁺ [16] and Sr₃Y(PO₄)₃: Dy³⁺ [17], etc.

Herein, we present Dy³⁺ doped Ca₉Gd(PO₄)₇ phosphors synthesized through solid state reactions. The structure, morphology, luminescence properties and energy transfer from Gd³⁺ to Dy³⁺ were investigated in detail. The application of these phosphors for wLEDs has also been referred.

2 Experimental

2.1 Sample preparation

TheCa₉Gd_1−x(PO₄)₇: xDy³⁺ (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18) phosphors were synthesized via conventional high temperature solid state reactions. High purity powders of CaCO₃ (99%), Gd₂O₃ (99.99%), (NH₄)H₂PO₄ (99%) and Dy₂O₃ (99.99%) were weighed according to a certain stoichiometric ratio as starting materials. Then, the weighed powders were mixed thoroughly in an agate mortar. Subsequently, the mixtures were placed in alumina crucibles followed by calcination in a tubular furnace at 1200 °C for 6 h in air. Finally, the samples were cooled down to room temperature (RM) naturally and ground into powder for characterization.

2.2 Sample characterization

The phase purity of as-prepared samples were employed by a PGENERAL XD-2 powder X-ray diffractometer with Cu-Kɑ irradiation (λ = 1.5406 Å) under 36 kV tube voltage and 20 mA tube current in 2θ ranging from 10° to 70°.The morphology of the samples was evaluated by a Hitachi S-3400N scanning electronic microscope (SEM) under 15 kV accelerating voltage. The photoluminescence (PL) and photoluminescence excitation (PLE) spectra were recorded using a Hitachi F-7000 fluorescence spectrophotometer equipped with a 150W Xe light source under 400V working voltage. The luminescence decay times were measured by an Edinburgh Instruments FLS-980 fluorescence spectrophotometer equipped with a 450 W Xenon lamp as the excitation source under 400 V working voltage. Diffuse reflectance spectra (DRS) were carried out with a Shimadzu UV-2450 UV–VIS-NIR spectrophotometer. Quantum efficiency and temperature-dependent PL spectra from room temperature to 300 °C were measured by another fluorescence spectrometer (Jobin Yvon Triax 320) equipped with double excitation mono-chromators and a homemade high temperature sample heater. Except for temperature-dependent PL spectra, all the measurements were carried out at RM.

3 Results and discussion

3.1 Phase purity

Figure 1 shows the X-ray diffraction (XRD) patterns of Ca₉Gd_1−x(PO₄)₇: xDy³⁺ phosphors with varied doping concentration of Dy³⁺(x). All the diffraction peaks of Ca₉Gd_1−x(PO₄)₇: xDy³⁺ phosphors can be indexed to the standard power diffraction card of Ca₉Y(PO₄)₇ (JCPDS No. 46-0402). No other secondary impurity phase is detected. This indicates that Ca₉Gd(PO₄)₇ has the same crystal structure as the Ca₉Y(PO₄)₇. The doping of Dy³⁺ with a small doping concentration does not change the crystal structure of Ca₉Gd(PO₄)₇. The effective radii of involved cations were reported as follows: R (Ca²⁺) = 100 pm, R (Gd³⁺) = 93.8 pm, R (Dy³⁺) = 91. 2 pm, R (P⁵⁺) = 17 pm [18]. On the basis of their identical charge and similar ionic radii, Dy³⁺ most probably occupies Gd³⁺ sites.

Fig. 1

XRD patterns of samples Ca₉Gd_1−x(PO₄)₇: xDy³⁺ (x = 0, 0.10, 0.18), the standard pattern of JCPDS card No. 46–0402 is also listed for comparison

3.2 Morphology observation

In order to observe the surface morphology of the synthesized phosphors, SEM observation was carried out. The typical SEM images are shown in Fig. 2. It is obviously observed that the samples consist of aggregated particles with a particle size ranging from 1 to 3 µm.

Fig. 2

SEM images of a representative sample Ca₉Gd_0.88(PO₄)₇: 0.12Dy³⁺ phosphor

3.3 DRS research

Figure 3 depicts the DRS of un-doped Ca₉Gd(PO₄)₇ and a representative sample Ca₉Gd_0.88(PO₄)₇: 0.12Dy³⁺. It shows a noticeable absorption edge at about 320 nm. Before 320 nm, there are two absorption bands peaking at 273 and 214 nm. The former can be attributed to the ⁸S_7/2 → ⁶I_J transition of Gd³⁺ ions whereas the latter might be related to the transition of the other cation in the host.

Fig. 3

DRS of Ca₉Gd(PO₄)₇ and Ca₉Gd_0.88(PO₄)₇: 0.12Dy³⁺

The band gaps of the un-doped and Dy³⁺ doped phosphors were calculated according to the DRS. The ratio of the light scattered from a thick layer of sample and ideal non-absorbing reference sample is measured as a function of the wavelength λ, R_∞ = R_sample/R_reference. In the diffuse reflectance spectra, the relation between absorption and scattering can be described via Kubelka–Munk Equation [19, 20]:

$$F({R_\infty })=\frac{{{{(1 - {R_\infty })}^2}}}{{2{R_\infty }}}=\frac{K}{S}$$

(1)

where R_∞ is the diffuse reflectance of the sample, K is absorption coefficient and S is scattering coefficient.

Furthermore, on the basis of Tauc relation, the band gap E_g and linear absorption coefficient α of a material can be expressed as follows:

$$\alpha h\nu =C{}_{1}{(h\nu - {E_g})^{\frac{n}{2}}}$$

(2)

where hν and C₁is the photon energy and proportionality constant, respectively.

When the material scatters in perfectly diffuse manner (or when it is illuminated at 60 °C incidence), the absorption coefficient K becomes equal to 2α. Concerning that the scattering coefficient S as constant with respect to wavelength, and using Eqs. (1) and (2), it can be derived that:

$${[F\left( {{R_\infty }} \right)h\nu ]^2}={C_2}{(h\nu - {E_g})^n}$$

(3)

The value of n is equal to 1, 2, 3, 4 and 6 for direct allowed transitions, non-metallic materials, direct forbidden transitions, indirect allowed transition and indirect forbidden transitions, respectively. Now, among the plot of [F(R_∞) hν]², [F(R_∞) hν], [F(R_∞) hν]^2/3, [F(R_∞) hν]^1/2, [F(R_∞) hν]^1/3 versus a function of photon energy hν, the best fitting was obtained when n = 1 in Eq. (3), which indicating that the band transitions took place are direct in nature. Therefore, the band gaps of Ca₉Gd(PO₄)₇ and Ca₉Gd_0.88(PO₄)₇: 0.12Dy³⁺ were ascertained to be 3.88 and 3.87 eV by extrapolating the lines to [F(R_∞) hν]²=0, according to the plot of [F(R_∞) hν]² versus hν, as shown in Fig. 4 (a) and (b).These values are similar to that of compounds with similar structure such as Ca₈MgBi(PO₄)₇(3.27 eV) [21], Sr₉Sc(PO₄)₇(3.92 eV) [22], Ca₉La(PO₄)₇ (3.96 eV) [23], Ca₁₀Na(PO₄)₇(4.1 eV) [24], and Ca₉Bi(PO₄)₇(4.25 eV) [25].

Fig. 4

Band gap values of Ca₉Gd(PO₄)₇ (a) and Ca₉Gd_0.88(PO₄)₇: 0.12Dy³⁺ (b)

The top of the valence band of these compounds is mostly formed by O 2p and P3s, 3p states [26]. However, the bottom of conduction band is related with the other cation except for phosphorus ions. Thus the variation of band gap energy around 4 eV is mainly related to cation except for phosphorus ions. In this case, Ca²⁺ and Gd³⁺ are involved, which is embodied in the DRS. It is worth noting that the doping of luminescent centers can also change the band gap energy more or less. Zhang et al. found that the doping of Eu³⁺ with a content of 70% can increase the band gap energy of Ca₈MgBi(PO₄)₇ from 3.27 to 3.38 eV [21]. Our recent investigation also shows that the doping of Eu³⁺ with a big concentration can increase the band gap of Ca₉La(PO₄)₇ [23]. However, in this work, the band gap of Ca₉Gd_0.88(PO₄)₇: 0.12Dy³⁺ is slightly smaller than that of Ca₉Gd(PO₄)₇. There might be two reasons for this difference. On the one hand, Eu³⁺ in inorganic compounds can form O²⁻ → Eu³⁺ charge transfer band in the PLE spectra. This can remarkably change the band structure of inorganic compounds. However, there are only some sharp excitation peaks in the PLE spectra of Dy³⁺ doped phosphors. On the other hand, the doping concentration of Eu³⁺ is often much bigger than that of Dy³⁺, even as high as 100%. Further research is needed to obtain deeper reasons.

3.4 Luminescence properties

The photoluminescence excitation (PLE) spectra with different doping concentration of Dy³⁺ monitoring the emission at 570 nm are displayed in Fig. 5. It is apparent that the PLE spectra comprises two parts: the first part from 250 to 320 nm contains tow peaks centered at 273 and 293 nm, corresponding to the ⁸S_7/2 → ⁶I_7/2 and ⁸S_7/2 → ⁶P_7/2 transitions of Gd³⁺ in the host [27, 28], respectively; and the other part from 300 to 460 nm consists of several bands located at 310, 323, 337, 350, 362, 386, 425 and 451 nm, which respectively results from ⁶H_15/2 → ⁴D_7/2, ⁶H_15/2 → ⁶P_3/2, ⁶H_15/2 → ⁴F_5/2, ⁶H_15/2 → ⁶P_7/2, ⁶H_15/2 → ⁶P_5/2, ⁶H_15/2 → ⁶M_21/2, ⁶H_15/2 → ⁴G_11/2 and ⁶H_15/2 → ⁴I_15/2 in the 4f⁹ electronic configurations of the Dy³⁺ ions [17]. The appearance of excitation peaks corresponding to Gd³⁺ in the PLE spectrum of Dy³⁺ doped samples indicates the occurrence of energy transfer from Gd³⁺ to Dy³⁺.

Fig. 5

PLE spectra of samples with different doping concentration of Dy³⁺ monitoring the emission at 570 nm (The inset shows the relationship of excitation intensity and doping concentration of Dy³⁺)

As illustrated in Fig. 6, the photoluminescence (PL) spectra of Dy³⁺ of samples excited at 350 nm mainly consist of three emission peaks at 480, 570 and 659 nm, which can be assigned to the optical transitions ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → ⁶H_11/2 of Dy³⁺, respectively. The inset of Fig. 6 shows the relationship between the relative intensity of ⁴F_9/2 → ⁶H_15/2 transition and the doping concentration of Dy³⁺. As the concentration increases, the emission intensity increases and reaches the maximum value at x = 0.12, which is taken as the optimum concentration. Beyond this optimum concentration, the intensity decreases due to the well-known concentration quenching effect.

Fig. 6

PL spectra of samples with different doping concentration of Dy³⁺ excited with 350 nm (The inset shows the relationship of emission intensity and doping concentration of Dy³⁺)

In addition, it is generally accepted that when Dy³⁺ are located at high-symmetry sites with inversion centers, ⁴F_9/2 → ⁶H_15/2 magnetic dipole transition (blue emission)is dominant while ⁴F_9/2 → ⁶H_13/2 electric dipole transition (yellow emission) is prominent as Dy³⁺ ions are located at low-symmetry sites without inversion centers. In our experiment, the intensity at 480 nm is stronger than that at 570 nm for each samples, as displayed in Fig. 6, certifying that Dy³⁺ ions tend to occupy high-symmetry sites in the host.

3.5 Concentration effect

The concentration quenching phenomenon can be ascribed to non-radiative transition process between the activators and it can be represented by the critical distance R_c, the shortest average distance between the nearest activator Dy³⁺ ions at a critical concentration x_c.

Hence, the critical transfer distance (R_c) was described by Eq. (4) according to Blasse [29, 30].

$${R_c} \approx 2{\left( {\frac{{3V}}{{4\pi {x_c}N}}} \right)^{\frac{1}{3}}}$$

(4)

Here x_c is the critical concentration from Fig. 6, N is the number of available sites in the unit cell which can be occupied by Dy³⁺ ions, and V is the volume of the unit cell. In this case, x_c= 0.12, N = 6 and V = 3525.89 ų. Then, the value of R_c is calculated to be ~ 21.07 Å.

There are several mechanisms responsible for energy transfer, that is, radiation re-absorption, exchange interaction and multi-polar interaction [31, 32]. Radiation re-absorption needs an overlap between PLE spectrum of activators and PL spectrum of sensitizers. In this case, both activator and sensitizer are Dy³⁺. There is no spectral overlap between PLE spectrum of activators and PL spectrum of sensitizers. Thus, radiation re-absorption is not accountable for the energy transfer among Dy³⁺. Exchange interaction is usually accountable when the critical distance is smaller than 5 Å. The critical distance in this case is 21.07 Å which is much larger than 5 Å. In consequence, multi-polar interaction is the most important mechanism for energy transfer among Dy³⁺. Concentration quenching mainly takes place due to electric multi-polar interaction among Dy³⁺.

The type of the multi-polar interaction can be determined by the following Eq. (5) [32]:

$$\frac{I}{x}=K{\left[ {1+\beta {{(x)}^{\frac{Q}{3}}}} \right]^{ - 1}}$$

(5)

Here I is the emission intensity at activator concentration x, K and β are the constants under the same excitation condition in a specific host lattice. The values of Q = 6, 8, 10 correspond to dipole–dipole (d–d), dipole–quadrupole (d–q) and quadrupole–quadrupole (q–q) interactions, respectively. According to Eq. (5), the curve of log(I/x) vs. log(x) for the ⁴F_9/2 → ⁶H_15/2 transitions of Dy³⁺ ions in Ca₉Gd_1 − x(PO₄)₇: xDy³⁺ is shown in Fig. 7. The fitting result in the region of high concentrations appears to be linear with a slope (− Q/3) = 1.62 which is approximately 2. The calculated value Q is approximately 6,which manifests that the d–d interaction is dominant for Dy³⁺ emission quenching mechanism in Ca₉Gd(PO₄)₇ host.

Fig. 7

The relationship of the concentration of Dy³⁺ ions log(x) and the log(I/x) for the ⁴F_9/2 → ⁶H_15/2 transitions

3.6 Decay times

The luminescence decay curves of Ca₉Gd_1−x(PO₄)₇: xDy³⁺ phosphors recorded for the wavelength of 480 nm (⁴F_9/2 → ⁶H_15/2)are presented in Fig. 8. Evidently, the curves are successfully fitted by bi-exponential equation as follows [33]:

$$I={A_1}{e^{{{ - t} \mathord{\left/ {\vphantom {{ - t} {{\tau _1}}}} \right. \kern-0pt} {{\tau _1}}}}}+{A_2}{e^{{{ - t} \mathord{\left/ {\vphantom {{ - t} {{\tau _2}}}} \right. \kern-0pt} {{\tau _2}}}}}$$

(6)

where I is the luminescence intensity; τ₁ and τ₂ are decay times for the exponential components; t is the time after excitation.

The average decay time τ_av can be calculated with the following equation:

$${\tau _{av}}=\frac{{{A_1}\tau _{1}^{2}+{A_2}\tau _{2}^{2}}}{{{A_1}{\tau _1}+{A_2}{\tau _2}}}$$

(7)

Fig. 8

Luminescence decay curves of Ca₉Gd_1 − x(PO₄)₇: xDy³⁺ (x = 0.04, 0.08, 0.12, 0.16) phosphors excited at 350 nm and monitored at 480 nm

The calculated average decay time τ_av are 0.499, 0.490, 0.443 and 0.420 ms, corresponding to x = 0.04, 0.08, 0.12 and 0.16, respectively. It is conspicuous that as the doping concentration of Dy³⁺increases, the lifetime decreases gradually, which is put down to the decreasing average distance between the Dy³⁺ ions bring about the energy transfer between the Dy³⁺ ions. Owing to the energy transfer, the decay time decreases with the increasing rate of the non-radiative and self-absorption.

3.7 CIE chromaticity coordinates

The ratio of yellow to blue (Y/B) integrated emission intensity is usually used to estimate the distortion around Dy³⁺ ions [34, 35]. Also, the line linking the blue and yellow wavelength usually passes through the white light region according to the CIE 1931 chromaticity diagram, thus, the Y/B ratio is worth investigating. The calculated Y/B value for each sample is stable between 0.79 and 0.84, which strongly demonstrates that Dy³⁺ occupy high-symmetry sites in the host and the concentration of Dy³⁺ has little influence on the Ca₉Gd(PO₄)₇ crystal structure.

To further represent the color emission of the phosphors, a Commission International de I’Eclairage (CIE) plot is plotted in Fig. 9. The chromaticity coordinates of each sample with varied Dy³⁺ doping concentration were calculated from the PL spectra under 350 nm excitation. They were located at white region at approximate (0.272, 0.322) for Dy³⁺ doped phosphors.

Fig. 9

CIE plot of Ca₉Gd_1 − x(PO₄)₇: xDy³⁺ phosphors

3.8 Energy transfer from Gd³⁺ to Dy³⁺

As mentioned above, the ⁸S_7/2 → ⁶I_7/2 and ⁸S_7/2 → ⁶P_7/2 transitions of Gd³⁺ ions in the host are clearly shown in the PLE spectra. Hence, energy transfer from Gd³⁺ to Dy³⁺ may occur in the Ca₉Gd_1−x(PO₄)₇: xDy³⁺ phosphor. To further investigate the energy transfer process, the PLE and PL spectra of un-doped Ca₉Gd(PO₄)₇ are shown in Fig. 10a and b. The sharp line at 273 nm originates from the ⁸S_7/2 → ⁶I_7/2 transition of Gd³⁺ ions, whereas the intensity emission line at 310 nm is ascribed to the ⁶P_7/2 → ⁸S_7/2 transitions. Meanwhile, the PL spectra of Ca₉Gd_0.88(PO₄)₇: 0.12Dy³⁺ pumped with 273 nm ultraviolet were measured, which is similar to the PL spectra pumped with 350 nm, consisting of two strong bands and a much weaker band, as depicted in Fig. 10d. The PLE spectra of Ca₉Gd_0.88(PO₄)₇: 0.12Dy³⁺ are also displayed in Fig. 10c. Furthermore, the strong sharp peak located at 310 nm can be detected, which stems from ⁸S_7/2 → ⁶I_7/2 transition of Gd³⁺ ions. The phenomenon clearly certifies that energy transfer from Gd³⁺ to Dy³⁺ does take place.

Fig. 10

PLE (a) and PL (b) spectra of un-doped Ca₉Gd(PO₄)₇, PLE (c) and PL (d) spectra of Ca₉Gd_0.88(PO₄)₇: 0.12Dy³⁺

As vividly displayed in Fig. 11, energy level diagram shows the energy transfer process from Gd³⁺ to Dy³⁺in Ca₉Gd_1−x(PO₄)₇: xDy³⁺. Under the excitation of 273 nm UV light, electrons of Gd³⁺ in Ca₉Gd_1−x(PO₄)₇: xDy³⁺ are excited to the excited state of ⁶I from the ground state of ⁸S_7/2 of Gd³⁺. Afterwards, the energy is transferred to the ⁶P_3/2 level of Dy³⁺. Subsequently, there is a non-radiative transition process among the excited states which resulted in transfer of electrons to the level of ⁴F_9/2. Ultimately, electrons return to ground states of Dy³⁺ and thereby give the characteristic emission [36, 37].

Fig. 11

Energy level diagram showing the energy transfer process from Gd³⁺ to Dy³⁺

3.9 Quantum efficiency and thermal stability

Quantum efficiency and thermal stability of phosphors are two essential indexes to present the luminescence performance and to evaluate the suitability for the solid-state lighting applications. The internal quantum efficiency and external quantum efficiency of Ca₉Gd_0.88(PO₄)₇: 0.12Dy³⁺ are experimentally determined to be 19.9 and 9.2% under 350 nm excitation, respectively. Although these values do not seem to be high, considering that our preparation conditions are not optimal, these values have a room for further improvement.

Temperature-dependent PL spectra from 25 to 300 °C of a typical sample Ca₉Gd_0.88(PO₄)₇: 0.12Dy³⁺ are measured. With the increment of the temperature, the integral PL intensity decreases gradually. The relationship of the integral PL intensity of one representative sample Ca₉Gd_0.88(PO₄)₇: 0.12Dy³⁺ with temperature is shown in Fig. 12. With the increment of the temperature, the PL intensity decreases gradually for the well-known temperature quenching. The PL intensity at 100, 150 and 200 °C is about 85, 76, and 59% of the one at room temperature (25 °C), respectively. This indicates that our phosphors present a better thermal stability.

Fig. 12

Relationship of the integral PL intensity of one representative sample Ca₉Gd_0.88(PO₄)₇: 0.12Dy³⁺ with temperature

4 Conclusions

In summary, a series of white light emitting phosphors Ca₉Gd(PO₄)₇: Dy³⁺ were successfully prepared through solid state reactions. Obtained phosphors show strong emissions at around 480 and 570 nm as well as a feeble emission peak at 659 nm upon excitation with 350 nm UV light. Blue emission is prominent. This indicates that Dy³⁺ ions are located at high-symmetry sites with inversion centers. The optimum doping concentration of Dy³⁺ is experimentally determined to be 12 mol%. The concentration quenching mechanism is ascertained to be electric dipole–dipole interaction between Dy³⁺ ions. Moreover, the mechanism of energy transfer from Gd³⁺ to Dy³⁺ is investigated. The band gaps of un-doped and Dy³⁺ doped Ca₉Gd(PO₄)₇ were calculated to be 3.88 and 3.87 eV, respectively. The internal quantum efficiency and external quantum efficiency of as-obtained phosphors under 350 nm excitation are determined to be 19.9 and 9.2%, respectively. The PL intensity at 100, 150, and 200 °C is about 85, 76, and 59% of the initial intensity at room temperature, respectively. Our studies indicate that our phosphors have potential applications in solid-state luminescence.