Trivalent terbium (Tb 3+ ) doped double molybdate AGd(MoO 4 ) 2 (A = Li + , Na + ) phosphors have been synthesized by combustion reaction. The crystal structures and luminescent properties of the phosphors are investigated in this paper. The XRD patterns indicate that AGd(MoO 4 ) 2 :Tb 3+ phosphors take on single phase when the precursors are sintered at 700 • C for 3 h. The average crystal size is about 2.0 μm. LiGd(MoO 4 ) 2 :Tb 3+ and NaGd(MoO 4 ) 2 :Tb 3+ phosphors have the similar luminescent properties. The influences of urea and Tb 3+ concentration on the luminescent properties of phosphor samples are also discussed in detail. The results show that Tb 3+ activated LiGd(MoO 4 ) 2 phosphors is a potential candidate for green phosphor in ultraviolet (UV) -based white LED.During the past decade, white light emitting diodes (LEDs) are paid more and more attentions owning to its some advantages, for example, long lifetime, low energy consumption, and naught pollutants. It is well known that there are two approaches to generate white LED. 1-3 One is the combination of different color light emitted by tricolor chips; the other is the combination of different colors obtained by converting the emission of blue or ultraviolet (UV) LED to longer-wavelength light using phosphors. The latter approach has been investigated widely and many red, green and blue phosphors have been developed. 4-6 Phosphors with high luminescent efficiency, stable and low cast are expected.Some experimental results indicate that double molybdate AGd(MoO 4 ) 2 (A = Li + , Na + ) share scheelite-like (CaMoO 4 ) structure, which shows excellent thermal and hydrolytic stability. Thus, they are deemed to be an potential host material. 7-9 Especially, Mo is coordinated by four O 2− ions in tetrahedral symmetry (T d ), which makes MoO 4 2− relatively stable and suitable for host material. 10,11 Tb 3+ -doped materials have been widely used as the green emitting phosphors due to their intense 5 D 4 → 7 F 5 emission in the green spectral region. Previous investigations show that Tb 3+ -doped aluminates or phosphates exhibit relatively strong absorption in the near-UV region and intense green emission with good color purity. 12,13 In this paper, Tb 3+ doped AGd(MoO 4 ) 2 green phosphors are fabricated by combustion reaction and their luminescent properties are investigated in this paper.
ExperimentalStoichiometric ratio of reactants in combustion reaction is calculated using the total valences of oxidizer (O) and reducer (R) and the energy released in the process of complete combustion is maximum when the ratio of O to F is 1 (O/F = 1). 14, 15 In this experiment, the valences of LiNO 3 (or NaNO 3 ), (NH 4 ) 6 Mo 7 O 24 , Gd(NO 3 ) 3 and urea are 5−, 18+, 15− and 6+, respectively. Thus, the theoretical equation for the formation of these phosphors, may be written as Eq. 1:where A is Li or Na. Moreover, excess urea was needed in order to compensate the loss of urea in combustion reactions. A series of Tb 3+ doped AGd(MoO 4 ) 2 phosphors were obtained by c...
