Efficient Bi3+ to Eu3+ energy transfer and color tunable emissions in K7CaY2(B5O10)3-based phosphors.

Abstract

Rare-earth borates are well known good photoluminescent materials due to the easy manipulation of activator concentration. K7CaY2(B5O10)3 belongs to a recently discovered borate family with outstanding nonlinear optical performances. A systematic study on Bi3+ and Eu3+ doped phosphors was performed to explore their potential in photoluminescence. K7Ca(Y1-xBix)2(B5O10)3 (0.01 ≤x≤ 0.06), K7Ca(Y1-yEuy)2(B5O10)3 (0.10 ≤y≤ 1) and K7Ca(Y0.99-zBi0.01Euz)2(B5O10)3 (0.05 ≤z≤ 0.90) were prepared by high temperature solid state reactions. Rietveld refinements reveal an 8% anti-site occupancy of Ca2+ and Eu3+ in K7CaEu2(B5O10)3, and two sets of Bi3+ emission and excitation spectra are also observed once Bi3+ is introduced. For instance, the two strongest 1S0→3P1 excitations at 270 nm and 281 nm correspond to two 3P1→1S0 emissions at 383 and 334 nm, respectively. The Eu3+ emission shows a maximal intensity at y = 0.50 under charge transfer excitation, while there is no concentration quenching effect under f-f excitation. The Bi3+-to-Eu3+ energy transfer is firmly supported by the steady photoluminescence spectra and the decreased lifetime of Bi3+ upon increasing the Eu3+ content in K7Ca(Y0.99-zBi0.01Euz)2(B5O10)3. This energy transfer mechanism occurs through the electric dipole-dipole interaction. Under excitation at 281 nm, the emission is tunable from deep blue (Bi3+) to pink and finally to red (Eu3+) all with high quantum yields (>80%).