Synthesis And Photoluminescence Properties Of Ti⁴⁺ And Eu³⁺ Doped Or Codoped M₂sno₄(m=ca, Sr, Ba) Phosphors

M₂SnO₄:Ti⁴⁺(M=Ca,Sr,Ba), M₂SnO₄:Eu³⁺(M=Ca,Sr,Ba) and M₂SnO₄:(Eu³⁺,Ti⁴⁺) (M= Ca,Sr, Ba) phosphor powders were synthesized with a solid-state reaction method and their luminescent properties were investigated by use of testing techniques such as X-ray diffraction (XRD), fluorescence spectra, decay lifetime and etc. The XRD results reveal that the crystal structure of M₂SnO₄ remains unchanged in Ti⁴⁺-doped, Eu³⁺-doped or Ti⁴⁺-Eu³⁺-codoped M₂SnO₄ phosphor powders. Broad emission bands of Ti⁴⁺-O^2- in the blue range were apparently observed in M₂SnO₄:Ti⁴⁺ samples. Their peaks located at about 22700 cm^-1, 24100 cm^-1 and 23500 cm^-1, respectively. Among which the emission intensity of Ca₂SnO₄:Ti⁴⁺ is strongest and the Ba₂SnO₄:Ti⁴⁺ is weakest. In these Ti-doped alkaline-earth stannate samples, the transition between Ti⁴⁺ and O^2- shows two excitation peaks in UV region. For the strong transition peak, the position (35900 cm^-1) of Ca₂SnO₄:Ti⁴⁺ locates between Ba₂SnO₄:Ti⁴⁺(35400 cm^-1)and Sr₂SnO₄:Ti⁴⁺(36500 cm^-1). But for the weak transition peak, the energy level of Ca₂SnO₄:Ti⁴⁺(39500 cm^-1)is higher than Ba₂SnO₄:Ti⁴⁺(37900 cm^-1)and Sr₂SnO₄:Ti⁴⁺(39200 cm^-1). The lifetime of Ti⁴⁺-O^2- luminescence to the phosphors in the one- dimension chain structure of Ca₂SnO₄:Ti⁴⁺ is about 2.66μs, which is increased to about 3.7μs in the two-dimension structure of Sr₂SnO₄:Ti⁴⁺ and Ba₂SnO₄:Ti⁴⁺.The emission intensity of Ca₂SnO₄:Eu³⁺ is strongest in all of M₂SnO₄:Eu³⁺ (M=Ca,Sr,Ba) samples. For the emission spectra, Ca₂SnO₄:Eu³⁺ phosphor powders exhibit bright red emission under UV excitation and the prime transition is electric dipole. Sr₂SnO₄:Eu³⁺ phosphor powders contain both 5D0-7F1 and 5D0-7F2 transition, while only the former transition appears in the phosphor powders of Ba₂SnO₄: Eu³⁺. For the excitation spectra, it is observed that all M₂SnO₄:Eu³⁺(M=Ca,Sr,Ba) samples exhibit broad absorption band of Eu³⁺-O^2-, and the band red shifts with increase of the Eu³⁺ concentrations. The experimental results about the emission spectra, excitation spectra and fluorescence decay time show that Eu³⁺+ ion substitutes for the Ca2 + ion in Ca₂SnO₄: Eu³⁺+ samples, but Eu³⁺+ ions can replace both Sr²⁺/ Ba²⁺ and Sn4+ ions in Sr₂SnO₄:Eu³⁺ and Ba₂SnO₄:Eu³⁺ samples, which occupy two types of sites in the crystallite.In Ti⁴⁺-doped Ca₂SnO₄:Eu³⁺ samples, Ti⁴⁺ can enhance the emission intensity originating from ⁵D₀-⁷F₁ and ⁵D₀-⁷F₂ transition in Eu³⁺ ion. The emission spectra of Ca2-xEuxSn1-yTiyO4 vary considerably with the concentration of Eu³⁺. Blue emission of Ti⁴⁺-O^2- and red luminescence of Eu³⁺ coexist in Ca_2-xEu_xSn_1-yTi_yO₄ with low concentration of Eu³⁺ whereas only the latter occurs with higher Eu³⁺ concentrations. It follows that changing the doping concentration of Eu³⁺ ion in samples can adjust the emitting waveband from blue to white and then to red. The lifetime of Ti⁴⁺-O^2- luminescence is about 2.83μs while that of Eu³⁺ emission is about 1275μs. The blue luminescence of Ca2-xEuxSn1-yTiyO4 originates from the charge-transfer absorption of Ti⁴⁺-O^2-. However, its red emission results from broadband UV absorption peak at about 275nm. There may be energy transfer between Ti⁴⁺ and Eu³⁺ ions.When the doped concentration of Eu³⁺ is very low, the charge-transfer-state (CTS) band of Ti⁴⁺-O^2- and 5D0-7F1 transition in Eu³⁺ can be apparently observed in Eu³⁺/Ti⁴⁺-codoped Sr₂SnO₄ and Ba₂SnO₄ samples. But when the concentration is very high, Ti⁴⁺-O^2- transition is very weak, and the intensity of Eu³⁺ emission decreases too. In Sr₂SnO₄:(Eu³⁺,Ti⁴⁺) samples, the energy of Ti⁴⁺-O^2- and Eu³⁺ emission are originating from the charge absorption of Ti⁴⁺-O^2-. Whereas in Ba₂SnO₄: (Eu³⁺,Ti⁴⁺) samples, the energy are due to the charge absorption of Ti⁴⁺-O^2- and Eu³⁺-O^2-, respectively.