Emacs abbrev table for Greek lower- and upper-case letters. See abbrev-mode for more.

greek-letters-abbrevs.el

(define-abbrev-table 'greek-abbrev-table
  '(
	;; Greek small letters
	("8al" "α")
	("8be" "β")
	("8ga" "γ")
	("8de" "δ")
	("8ep" "ε")
	("8ze" "ζ")
	("8et" "η")
	("8th" "θ")
	("8io" "ι")
	("8ka" "κ")
	("8la" "λ")
	("8mu" "μ")
	("8nu" "ν")
	("8xi" "ξ")
	("8oi" "ο") ;; omicron
	("8pi" "π")
	("8ro" "ρ")
	("8si" "σ")
	("8ta" "τ")
	("8up" "υ")
	("8ph" "φ")
	("8ch" "χ")
	("8ps" "ψ")
	("8oe" "ω") ;; omega

	;; Greek capital letters
	("8Al" "Α")
	("8Be" "Β")
	("8Ga" "Γ")
	("8De" "Δ")
	("8Ep" "Ε")
	("8Ze" "Ζ")
	("8Et" "Η")
	("8Th" "Θ")
	("8Io" "Ι")
	("8Ka" "Κ")
	("8La" "Λ")
	("8Mu" "Μ")
	("8Nu" "Ν")
	("8Xi" "Ξ")
	("8Oi" "Ο") ;; Omicron
	("8Pi" "Π")
	("8Ro" "Ρ")
	("8Si" "Σ")
	("8Ta" "Τ")
	("8Up" "Υ")
	("8Ph" "Φ")
	("8Ch" "Χ")
	("8Ps" "Ψ")
	("8Oe" "Ω") ;; Omega
))

;; As per your taste:
;; (setq save-abbrevs nil) ;; stop asking to save new abbrevs when quitting emacs
;; (setq-default abbrev-mode t) ;; turn on abbrev mode globally

;; N.B. You can insert funny characters in emacs using e.g. `C-x 8 RET GREEK SMALL LETTER LAMBDA'