The Synthesis,structure And Luminescence Properties Of Several Phosphors With Apatite Structure

As the next generation lighting source,white light emitting diodes（w-LEDs）have received extensive attention due to their excellent performance.The typical way to get w-LEDs is combining a blue LED chip with a broad band yellow Y3Al5O12: Ce³⁺ phosphor.However,such w-LEDs have low color rendering index and high correlated color temperature due to the lack of green and red light in the emission spectra.To solve this problem,w-LEDs fabricated using a near-ultraviolet（n-UV）InGaN-based LED chip combined with the（red,green,and blue）phosphors have been proposed and employed.Therefore,it is very important to develop novel single-colorand single phase multi-color phosphors.As we know,energy transfer and structure tuning are the main methods to get single phase multi-color phosphors.The apatite-type compounds can provide abundant crystal field environments by incorporating various foreign ions.In this paper,several novel phosphors with apatite structure were synthesized by high temperature solid-state reaction,and the effect of cationic isomorphous substitution,complex anion isomorphous substitution,cation and complex anionsynergeticisomorphous substitution on the structure and luminescence properties of these phose were investigated.In addition,the energy transfers of Eu²⁺/Tb³⁺ and Ce³⁺/Tb³⁺ were studied.The main achievements are asfollows:1.The Sr₁₀（PO₄）6O : Eu²⁺ phosphors were synthesized,and thephosphors exhibited a broad-band blue emission at 439 nm and strong thermal quenching resistance,Eu²⁺ can occupy two non equivalent Sr²⁺ sitesin Sr₁₀（PO₄）6O host.The effects of anion substitution on the structure and luminescent properties were studied.With the increase of [S04]2-and [Si04]4-substitution of [P04]3-,the average bond length between Eu²⁺ and O2-is reduced and the crystal field around Eu²⁺ is enhanced,resulting in the increase of crystal field splitting and centroid shift of the 4f65d1 energy level of Eu²⁺.Hence,the 4f65d1→4f7transition energy of Eu²⁺ decreased,resulting in the red-shift（439 nm to 539 nm）of the emission peak for Sr₁₀（PO₄）6-2x（SiO₄）x（SO₄）xO phosphors.2.The La_5.99Ce_0.01M₄（SiO₄）6F2（M = Ca,Sr,Ba）phosphors were synthesized,and the phosphors showed strong blue light emission with broad bands.The effects of cation substitution on the structure and luminescent properties were studied.With the of isomorphoussubstitute for Ca→Sr→Ba,the average bond length between Ce³⁺ and anions is increased and the crystal field around Ce³⁺ is weakened,resulting in the decreased of crystal field splitting and centroid shift of the 5denergy level of Ce³⁺.Therefore,the 5d→2F5/2 and 5d→2F7/2transition energy of Ce³⁺increased,resulting in the blue-shift（423 nm to 410 nm）of the emission peak for La_5.99Ce_0.01M₄（SiO₄）6F2（M = Ca,Sr,Ba）.3.The La_5.90-xBa_4+x（SiO₄）6-x（PO₄）xF2:0.10Ce³⁺（x= 0,1,2,and 3）phosphors were prepared,and the phosphors exhibited strong blue emission and thermal quenching resistance.The effects of cation and complex anion isomorphous synergetic substitution on the structure and luminescence properties were studied.With the increase of Ba²⁺ and [PO₄]3-isomorphous substitution for La²⁺ and [SiO₄]4-,the average bond length between Ce³⁺ and anions is increased and the crystal field around Ce³⁺ is weakened,resulting in the decrease of crystal field splitting and centroid shift of the 5denergy level of Ce³⁺.Therefore,the 5d→2F5/2 and 5d→2F7/2transition energy of Ce³⁺increased,resulting in the blue-shif（414 nm to 407 nm）of the emission peak for La_5.90-xBa_4+x（SiO₄）6-x（PO₄）xF2:0.10Ce³⁺（x= 0,1,2,and 3）.4.The Ba₁₀（PO₄）6O: Eu²⁺,Tb³⁺/Li+ phosphors were prepared,and the energy transfers between Eu²⁺ and Tb³⁺ can be observed in Ba₁₀（PO₄）6O.The energy transfer mechanism from Eu²⁺ to Tb³⁺maybe a quadrupole-quadrupole interaction.A prototype white lampwas packaged by mixing green phosphor Ba9.83（PO₄）6O: 0.03Eu²⁺,0.07Tb³⁺,0.07Li+,commercial red phosphor CaAlSiN3: Eu²⁺ and a 370 LED chip,and the lamp exhibited a higher color rendering index and warm correlated color temperature.The Lu5（SiO₄）3N: Ce³⁺,Tb³⁺ phosphors were synthesized,and two luminescence centres for Ce³⁺ inLu5（SiO₄）3N host can be observed.The energy transfers between Eu²⁺ and Tb³⁺ happens in Lu5（Si O₄）3N,and the energy transfer mechanism maybe a quadrupole-quadrupole interaction.In Ce³⁺ and Tb³⁺ co-doped Lu5（SiO₄）3N: Ce³⁺,Tb³⁺ compounds,the color can be tuned from blue to green by changing the relative doping amount of Ce³⁺ and Tb³⁺.