Home

• Summary
• Table of Contents

Introduction

• Introduction
• The Problem

Theory

• Photosynthesis
• Delayed Fluorescence
• Photosynthetic Herbicides

The method

• Treatment
• Registration
• Analysis

Reference

• Literature
• Abbreviations
• Index of Figures
• Links

---

Fluorescence

Sidebar: Fluorescence yield

The term fluoresecence yield, or quantum yield of fluorescence, φ_f , references the number of photons emitted as fluorescence relative to the total number of absorbed photons.

φ_f = F / I_a,

where F is the fluorescence intensity and I_a is the intensity of the absorbed light.

Then, the fluorescence intensity is equal to the intensity of the absorbed light times the fluorescence yield:

F = φ_f ×I_a

The quantum yields can be represented in terms of rate constants of the individual de-excitation reactions. The fluorescence yield would be equal to the rate constant of fluorescence over the sum of the rate constants of all de-excitation pathways:

φ_f = k_f / (k_p + k_f + k_d),

where k_f , k_p and k_d are the rate constants of, respectively, fluorescence, photochemistry and all other (non-radiative) de-excitation pathways.

At room temperature the chlorophyll fluorescence of native plants is generated predominantly by Photosystem 2 (Govindjee, 1995). According to the hypothesis of Duysens and Sweers (1963), the fluorescence yield is minimal when when the PS2 primary quinone acceptor Q_A is in its oxidised state. Such PS2 reaction centres are termed as "open". Conversely, when Q_A is reduced, the fluorescence is maximal and the reaction centre is "closed". For closed reaction centres, the effective rate of photochemistry is zero, and the fluorescence yield is

φ_f = k_f / (k_f + k_d)

Back to Fluorescence