Light conversion in thin films of a mixture of mesotetraphenylporphyrin and erbium-doped yttrium vanadate crystallites: 2. Optical properties

The optical properties of two-component films composed of mesotetraphenylporphyrin (TPP) and erbium-doped yttrium vanadate Yt_0.95Er_0.05VO₄ prepared by spincoating have been studied for the first time. A decrease in the TPP content in the films leads to a hypsochromic shift of the Soret band peak by 1–9 nm; this finding suggests that the degree of aggregation of TPP decreases with decreasing TPP content in the film. The fluorescence peak of TPP is located at an emission wavelength of λ_em = 634 nm and an excitation wavelength of λ_ex = 420 nm. The fluorescence peaks of Y_0.95Er_0.05VO₄ at λ_em = 526, 546, and 555 nm (λ_ex = 300 nm) correspond to the following transitions of the Er3+ ion: the band at 526 nm, to the ² H _11/2 → ⁴ I _15/2 transition; the bands at 546 and 555 nm, to the ⁴ S _3/2 λ ⁴ I _15/2 transition. The fluorescence band peaks preserve their positions with a change in the ratio of components in the film; that is, the fluorescent characteristics of TPP and Y_0.95Er_0.05VO₄ clusters do not depend on their interaction. For both TPP and Y_0.95Er_0.05VO₄, the maximum fluorescence intensity is observed at a TPP content in the film of 40%; the gain with respect to single-component TPP and Y_0.95Er_0.05VO₄ films is 70 and 4–15%, respectively. In this case, a significant effect is exerted not so much by the nature and structure of the components and their interaction as by the topographic features of organization of the photoactive elements in the film, their ratio, and mutual orientation, which determine the energy capture probability.